BAHAGIAN A – Pengesahan Kerjasama*
Adalah disahkan bahawa projek penyelidikan tesis ini telah dilaksanakan melalui
kerjasama antara _____________________ dengan ______________________
Disahkan oleh:
Tandatangan
: ………………………………….. Tarikh: ……………….
Nama
: …………………………………..
Jawatan
(Cop rasmi)
: …………………………………..
* Jika penyelidikan tesis/projek melibatkan kerjasama.
BAHAGIAN B – Untuk Kegunaan Pejabat Sekolah Pengajian Siswazah
Tesis ini telah diperiksa dan diakui oleh:
Nama dan Alamat
Pemeriksa Luar
:
Nama dan Alamat
Pemeriksa Dalam I
:
Pemeriksa Dalam II
:
Prof. Dr. Sahrim Bin Hj. Ahmad
School of Applied Physics
Faculty of Science & Technology
Universiti Kebangsaan Malaysia
43600 UKM Bangi, Selangor
Assoc. Prof. Dr. Wan Aizan Bt. Wan Abd. Rahman
Department of Polymer Engineering
Faculty of Chemical and Natural Resources
Engineering, Universiti Teknologi Malaysia
81310 UTM Skudai, Johor
Assoc. Prof. Dr. Shahrir Bin Hashim
Department of Polymer Engineering
Faculty of Chemical and Natural Resources
Engineering, Universiti Teknologi Malaysia
81310 UTM Skudai, Johor
Nama Penyelia Lain :
(jika ada)
Disahkan oleh Timbalan Pendaftar di SPS:
Tandatangan :
………………………………….
Nama
…………………………………
:
Tarikh: ………………
MECHANICAL, THERMAL AND PROCESSING PROPERTIES OF OIL PALM
EMPTY FRUIT BUNCH-FILLED IMPACT MODIFIED UNPLASTICISED
POLY (VINYL CHLORIDE) COMPOSITES
AZNIZAM BIN ABU BAKAR
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Doctor of Philosophy
Faculty of Chemical and Natural Resources Engineering
Universiti Teknologi Malaysia
JANUARY 2006
ii
iii
To my beloved wife, parents, son and daughter…
iv
ACKNOWLEDGEMENT
I would like to express my sincere gratefulness and appreciation to my
supervisor, Associate Professor Dr. Azman Hassan for his tremendous encouragement
and endless support during my Ph.D. study. I learned the art of science throughout
your supervision. You taught me what is not taught in the course. I am very grateful to
Dr. Ahmad Fuad Mohd Yusof, my co-supervisor, from SIRIM. My special thanks to
my colleagues, all from Universiti Teknologi Malaysia, who provided constructive
and scientific advice for the completion of this thesis. This include: Dr. Afendi,
Munirah Mokhtar, Zainab Salleh, Sukor Ishak, Suhee Tan Hassan, Nordin Ahmad,
Ambiga Gopal, Jaafar, Jamil Tahir, Ahmad Norani Sadiron, Yahya Khalid, Arshad
Abu Hassan, Mazatusziha and Toh Soh Chong. I would also like to thank IRM,
especially Dato Karim, for providing PVC resins and additives, and allowing me to
use the Brabender Torque Rheometer equipment for pocessability studies. My special
thanks also go to Wan Ali from MINT for his assistance in extrusion processing.
This study will not to be accomplished without finance and therefore I would
like to express my appreciation to the Malaysia Government and Universiti Teknologi
Malaysia for the financial support.
Finally, I wish to thank to my beloved wife, son and daughter, Sukina, Ahmad
Afzanizam and Afza Firzana for their love, support, and understanding and most
importantly for their patience.
v
ABSTRACT
The main objective of this study is to investigate the effects of EFB filler and
two types of impact modifiers on mechanical and thermal properties, and
processability of PVC-U composites. Two methods were used to prepare the samples,
i.e., compression moulding and single screw extrusion. A torque rheometer was used
to determine the fusion characteristics of PVC. EFB increased the flexural modulus
of 22 % but decreased the impact strength and flexural strength of 20 % and 18 % of
PVC, respectively, as the filler contents increased. Increasing the impact modifiers
contents, on the other hand, improved the impact strength but slightly decreased the
flexural modulus and flexural strength. Acrylic impact modifier performed better than
CPE in producing composites with balanced properties of toughness and stiffness.
The use of Prosil 9234 coupling agent for filler surface treatment proved to be more
reliable compared to NZ 44 in providing better filler-matrix interaction. The TGA
study showed that both the EFB filler and acrylic impact modifier decreased the PVC
thermal stability. Oil residues in the EFB did not influence the mechanical properties
of PVC-U composites. The fusion time also decreased significantly with the addition
of acrylic. Both the temperature and screw speed significantly influenced the fusion
level of PVC, hence the mechanical properties of the extrudates. Overall, the study
showed that EFB has the potential to be used as filler for PVC-U composites.
vi
ABSTRAK
Objektif utama kajian ini ialah untuk menyelidik kesan pengisi EFB dan
pengubahsuai hentaman terhadap sifat mekanikal, terma dan kebolehanproses
komposit PVC-U. Dua kaedah telah digunakan untuk penyediaan sampel, iaitu
pengacuan mampatan dan penyemperitan berskru tunggal. Reometer tork telah
digunakan untuk menentukan ciri-ciri pelakuran PVC. EFB telah meningkatkan
modulus lenturan sebanyak 22 % tetapi telah mengurangkan kekuatan hentaman PVC
sebanyak 20 % dan kekuatan lenturan sebanyak 18 % apabila meningkatnya
kandungan pengisi. Peningkatan kandungan pengubahsuai hentaman sebaliknya telah
meningkatkan kekuatan hentaman tetapi mengurangkan sedikit modulus lenturan dan
kekuatan lenturan. Pengubahsuai hentaman akrilik telah menunjukkan prestasi yang
lebih baik dalam menghasilkan komposit bersifat kekukuhan dan kekakuan yang
seimbang berbanding CPE. Penggunaan agen gandingan Prosil 9234 untuk rawatan
permukaan pengisi telah menghasilkan interaksi pengisi-matrik yang lebih baik
berbanding dengan NZ 44. Kajian TGA menunjukkan bahawa pengisi EFB dan
pengubahsuai hentaman akrilik telah mengurangkan kestabilan terma PVC. Sisa
minyak pada EFB didapati kurang mempengaruhi sifat-sifat mekanikal komposit
PVC-U. Masa pelakuran juga telah menurun dengan penambahan kandungan akrilik.
Suhu dan laju skru telah mempengaruhi tahap lakuran PVC begitu juga sifat-sifat
mekanikal ekstrudat. Keseluruhannya kajian menunjukkan bahawa EFB berpotensi
digunakan sebagai pengisi di dalam komposit PVC.
vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
TITLE PAGE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xiii
LIST OF FIGURES
xviii
LIST OF SYMBOLS
xxv
INTRODUCTION
1
1.1
Overview
1
1.2
Significance of Study
4
1.3
Objectives of Study
6
1.4
Outline of Thesis
7
LITERATURE REVIEW
9
2.1
Poly (vinyl chloride)
9
2.1.1
Definitions and General Feature Properties
9
2.1.2
PVC Polymerisation
11
2.1.3
Morphology of PVC
13
viii
2.1.4
PVC Fusion
16
2.1.4.1 Mechanisms of Fusion
17
2.1.4.2 Fusion Level Assessment:
Differential Scanning Calorimetry
19
2.1.4.3 Interrelation between Fusion and
Properties
2.2
2.3
2.4
21
PVC and Additives
24
2.2.1
Stabilizer
24
2.2.2
Lubricants
26
2.2.3
Processing Aid
32
2.2.4
Pigment
34
2.2.5
Impact Modifier
35
Impact Modification
38
2.3.1
Theory of Impact Modification
38
2.3.2
Impact Modified PVC
40
Filled PVC Composites
42
2.4.1
Composites: Definitions and Categories
42
2.4.2
Filler and Reinforcement
44
2.4.2.1 Mineral Fillers
46
2.4.2.2 Organic Fillers
47
Filler-Matrix Interface
50
2.4.3
2.4.3.1 Coupling Agent and Surface
Modification
2.5
Oil Palm Empty Fruit Bunch-Polymer Composites
2.5.1
56
Theory of Mechanical Properties of Filled
Composites
2.7
55
Utilization of EFB Fibre in Polymer
Composites
2.6
54
Oil Palm Empty Fruit Bunch and its
Chemical Composition
2.5.2
51
59
Recent Studies on Impact Modified PVC-U by
UTM researchers
63
ix
3
MECHANICAL PROPERTIES OF COMPRESSION
MOULDED PVC-U COMPOSITES
65
3.1
Introduction
65
3.2
Experimental
67
3.2.1
Materials
67
3.2.2
Filler Preparations
69
3.2.3
Coupling Agent Treatment of Filler
71
3.2.4
Blend Formulations
72
3.2.5
Dry Blending
82
3.2.6
Two Roll Milling
82
3.2.7
Compression Moulding
84
3.2.8
Density Determination
85
3.2.9
Impact Testing
87
3.3
3.2.10 Flexural Testing
87
3.2.11 Accelerated Weathering Testing
88
3.2.12 Water Absorption Testing
89
3.2.13 Scanning Electron Microscopy Study
89
3.2.14 Fourier Transform Infra-Red Analysis
90
Results and Discussion
90
3.3.1
3.3.2
Density of the Filler and EFB-filled PVC-U
Composites
90
Mechanical Properties
92
3.3.2.1 Notched Izod Impact Strength
92
3.3.2.2 Flexural Properties
108
3.3.2.3 EFB-Filled Acrylic-Impact Modified
PVC-U Composites Treated with
Coupling Agents
120
3.3.2.4 Effect of Accelerated Weathering on
the Impact and Flexural Properties
137
3.3.2.5 Effect of NPCC on the Impact and
Flexural Properties
153
3.3.2.6 Effect of Extracted Filler on the
Impact and Flexural Properties
159
x
3.3.2.7 Water Absorption
3.4
4
Conclusions
167
THERMAL PROPERTIES OF COMPRESSION
MOULDED PVC-U COMPOSITES
169
4.1
Introduction
169
4.2
Experimental
171
4.2.1
4.3
4.4
5
162
Materials, Filler Preparation and Blend
Formulations
172
4.2.2
Sample Preparation
172
4.2.3
Heat Deflection Temperature Testing
172
4.2.4
Differential Scanning Calorimetry Study
173
4.2.5
Thermogravimetric Analysis
173
Results and Discussion
174
4.3.1
Heat Deflection Temperature
174
4.3.2
Glass Transition Temperature
177
4.3.3
Thermal Degradation Temperature
178
Conclusions
190
PROCESSABILITY STUDIES OF PVC-U
COMPOUNDS
192
5.1
Introduction
192
5.2
Experimental
195
5.2.1
Materials and Blend Formulations
195
5.2.2
Filler Preparation
195
5.2.2.1 EFB Oil Extraction
195
5.2.3
Dry Blending
197
5.2.4
Processability Study
198
5.2.5
Fourier Transform Infra-Red Analysis
198
5.2.6
Scanning Electron Microscopy Study
199
5.3
Results and Discussion
199
5.3.1
Fusion Characteristics
199
5.3.1.1 Effect of EFB Filler
201
5.3.1.2 Effect of Acrylic Impact Modifier
203
xi
5.3.1.3 Effect of CPE Impact Modifier
207
5.3.1.4 Effect of Temperature
212
5.3.2
Postulated Lubrication Mechanisms
214
5.3.3
Effect of Extracted EFB Filler on the
Processability of PVC-U Compound
219
5.3.3.1 Extractives Removal
219
5.3.3.2 FTIR Spectra
219
5.3.3.3 Extracted Filler Surface
222
5.3.3.4 Fusion Characteristics of Extracted
EFB-Filled PVC-U Compound
5.4
6
Conclusions
223
225
EXTRUSION PROCESS AND MECHANICAL
PROPERTIES OF EXTRUDATES
227
6.1
Introduction
227
6.2
Experimental
229
6.2.1
Materials
229
6.2.2
Dry Blending
230
6.2.3
Extrusion Process
230
6.2.4
Izod Impact and Flexural Testing
231
6.2.5
Tensile Testing
232
6.2.6
Differential Scanning Calorimetry Study
232
6.3
Results and Discussion
232
6.3.1
Extrudates Characteristics
233
6.3.2
Differential Scanning Calorimetry
238
6.3.3
Impact Strength
240
6.3.3.1 Effect of Processing Temperature
240
6.3.3.2 Effect of Screw Speed
244
Flexural Properties
246
6.3.4.1 Effect of Processing Temperature
246
6.3.4.2 Effect of Screw Speed
248
6.3.5
Tensile Properties
249
6.3.6
Yield Stress Analysis
255
6.3.7
General Discussion
258
6.3.4
xii
6.4
7
Conclusions
260
CONCLUSIONS AND SUGGESTIONS
FOR FUTURE WORK
262
7.1
Conclusions
262
7.2
Suggestions for Future Work
264
REFERENCES
266-282
xiii
LIST OF TABLES
TABLE NO.
2.1
TITLE
PAGE
Some physical properties of moulding PVC products
and compounds
11
2.2
PVC nomenclatures
15
2.3
Chemical analysis of EFB
55
3.1
Specifications of PVC suspension resin MH-66
68
3.2
Types of additives
68
3.3
Blend formulations
73
3.4
Effect of impact modifiers content on the impact strength
of PVC-U compounds
3.5
94
Percentage of impact strength reduction of EFB-filled
impact modified composites as filler content increased
from 10 to 40 phr
3.6
101
Percentage of impact strength increment for EFB-filled
impact modified composites as the impact modifier
content increased from 0 to 12 phr
3.7
107
Percentage of flexural modulus increment for EFB-filled impact
modified composites as the filler content increased
from 0 to 40 phr
3.8
114
Percentage of flexural strength reduction for EFB-filled
impact modified composites as the filler content increased
from 0 to 40 phr
3.9
Percentage of flexural modulus reduction for EFB-filled
impact modified composites as the impact modifier
114
xiv
increased from 0 to 12 phr
3.10
118
Percentage of flexural strength reduction for EFB-filled
impact modified composites as the impact modifier
increased from 0 to 12 phr
3.11
Impact strength of EFB–filled acrylic-impact modified
composites treated with Prosil 9234 and NZ 44
3.12
130
Comparison between the predicted and the experimental
of relative modulus of composites
3.15
130
Flexural strength of EFB–filled acrylic-impact modified
composites treated with Prosil 9234 and NZ 44
3.14
126
Flexural modulus of EFB–filled acrylic-impact modified
composites treated with Prosil 9234 and NZ 44
3.13
118
131
Comparison between the predicted and the experimental
of relative modulus of filled acrylic-impact modified composites
at 3 phr of acrylic
3.16
132
Comparison between the predicted and the experimental
of relative modulus of filled acrylic-impact modified
composites at 6 phr of acrylic
3.17
132
Comparison between the predicted and the experimental
of relative modulus of filled acrylic-impact modified composites
at 9 phr of acrylic
3.18
132
Comparison between the predicted and the experimental relative
flexural modulus of filled acrylic-impact modified composites at
12 phr of acrylic
3.19
Impact strength reduction for impact-modified compounds after
accelerated weathering for 504 hours
3.20
139
Percentage of impact strength reduction for filled impact modified
composites after weathered for 504 hours
3.21
133
142
Percentage of flexural modulus reduction and percentage of
flexural strength increment of the impact-modified compounds
after 504 hours exposure to accelerated weathering
3.22
Percentage of flexural modulus reduction and percentage
of flexural strength increment of the filled composites and filled
impact-modified composites after 504 hours exposure
146
xv
to accelerated weathering
3.23
Percentage of water absorption of impact modified
compounds and EFB-filled composites
3.24
163
Percentage of water absorption of impact modified
compounds and impact modified treated composites
4.1
146
166
HDT of acrylic-impact modified and CPE-impact
modified PVC-U compounds
175
4.2
HDT of EFB-filled PVC-U composites
176
4.3
HDT of EFB-filled acrylic-impact modified and
EFB-filled CPE-impact modified PVC-U composites
176
4.4
Tg of EFB-filled PVC-U composites
177
4.5
Tg of EFB-filled acrylic-impact modified and EFB-filled
CPE-impact modified PVC-U composites
4.6
Degradation temperature of neat components obtained
from TG and DTG curves
4.7
185
Degradation temperature of EFB-filled CPE-impact
modified PVC-U composites
4.9
180
Degradation temperature of EFB-filled PVC-U
composites obtained from TG and DTG curves
4.8
178
187
Degradation temperature of EFB-filled acrylic-impact
modified PVC-U composites obtained from TG and DTG
curves
5.1
Fusion characteristics of EFB-filled compounds at
50 rpm and 80 oC
5.2
202
Fusion characteristics of acrylic-impact modified
compounds at 50 rpm and 180 oC
5.3
189
204
Fusion characteristics of EFB-filled acrylic-impact
modified compounds added with 9 phr of acrylic at
50 rpm and 180 oC
5.4
205
Fusion characteristics of EFB-filled acrylic-impact
modified compounds filled with 20 phr of filler at
50 rpm and 180 oC
5.5
206
Fusion characteristics of CPE-impact modified
compounds at 50 rpm and 180 oC
208
xvi
5.6
Fusion characteristics of EFB-filled CPE-impact modified
compounds added with 9 phr CPE at 50 rpm and 180 oC
5.7
Fusion characteristics of EFB-filled CPE-impact modified
compounds filled with 20 phr of EFB at 50 rpm and 180 oC
5.8
211
Fusion time of PVC-U compounds at different processing
temperatures and constant rotor speed of 50 rpm
5.9
210
212
End torque of PVC–U compounds and composites at
different processing temperatures and constant rotor speed
of 50 rpm
5.10
214
Fusion characteristics of extracted EFB-filled PVC-U
compounds at 50 rpm and 180 oC.
224
6.1
The conditions of extrusion processing
231
6.2
Residence time of extrudates at constant die temperature
237
6.3
Residence time of extrudates at constant screw speed of 60 rpm
238
6.4
Heat of fusion of extrudates at screw speed of 60 rpm
240
6.5
Effect of processing temperatures on the fracture properties
of unfilled and filled extrudates
6.6
Effect of processing temperatures on the heat of fusion and
impact strength of unfilled extrudates
6.7
247
Effect of screw speeds on the flexural modulus of unfilled
and filled extrudates
6.14
247
Effect of processing temperatures on the flexural strength of
unfilled and filled extrudates
6.13
246
Effect of processing temperatures on the flexural modulus of
filled extrudates
6.12
244
Effect of processing temperatures on the flexural modulus
of unfilled extrudates
6.11
244
Effect of screw speeds on the impact strength of unfilled
and filled extrudates
6.10
243
Effect of screw speeds on the fracture properties of unfilled
and filled extrudates
6.9
241
Effect of processing temperatures on the heat of fusion and
impact strength of filled extrudates
6.8
241
Effect of screw speeds on the flexural strength of unfilled
249
xvii
and filled extrudates
6.15
Effect of processing temperatures on the yield stress of
unfilled extrudates at screw speed of 60 rpm
6.16
258
Predicted yield stress of extrudates at 3 m/s, die temperature
of 190 oC and screw speed of 60 rpm
6.24
255
Predicted yield stress of extrudates at 3 m/s, die temperature
of 180 oC and screw speed of 60 rpm
6.23
255
Effect of strain rate on the yield stress of unfilled and filled
extrudates
6.22
254
Effect of screw speed on the percentage strain at break at die
temperature of 180 oC
6.21
254
Effect of processing temperature on the percentage strain
at break of filled extrudates at screw speed of 60 rpm
6.20
251
Effect of processing temperature on the percentage strain
at break of unfilled extrudates at screw speed of 60 rpm
6.19
251
Effect of screw speeds on the yield stress of extrudates
at die temperature of 180 oC
6.18
250
Effect of processing temperature on the yield stress of
filled extrudates at screw speed of 60 rpm
6.17
249
258
Impact strength, yield stress and strain at break at die
temperature 180 oC and 190 oC
259
xviii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
The chemistry of vinyl chloride monomer production
12
2.2
PVC particle morphology
15
2.3
Mechanism of fusion during processing extruder
18
2.4
Schematic presentation of fusion process for
19
2.5
DuPont thermal analysis of PVC-U compound
compression moulded at different temperatures
2.6
20
Zip-elimination of HCl from PVC and simultaneous
formation of sequences containing conjugated
double bonds (polyenes) in the chain during degradation
2.7
25
A model of PVC lubrication (not to scale) showing metal
lubrication and lubrication between PVC primary particle
flow units for (a) no lubricant; (b) calcium stearate ;
(c) for paraffin ; and (d) calcium stearate and paraffin
2.8
29
Lubrication mechanism, showing metal lubrication
and lubrication between PVC micro particles flow units
of PVC/CPE, PVC/OPE and PVC/CPE/OPE compounds
2.9
31
Stress distribution in polymer matrix surrounding
a rubbery impact modifier particle
37
2.10
Aspect ratio calculation
46
2.11
Cellulose molecular structure
48
2.12
Bonding mechanism of silane coupling agent to filler’s surface
52
3.1
Chemical structure of (a) Prosil 9234 (b) NZ 44
69
3.2
EFB fillers distribution
70
xix
3.3
Morphology of EFB fillers (Magnification of 600x)
70
3.4
Two roll milling of PVC-U dry blend at 165 oC
83
3.5
Two-roll milled composite sheet
83
3.6
A mould with five cavities placed in between the hot platens
before compression
3.7
The theoretical and experimental densities of EFB-filled
composites (S9 - S12) with respect to EFB filler contents
3.8
84
91
SEM micrograph of impact-fractured surface of S11
(Magnification 2000x)
92
3.9
Hinge breaks of impact-modified PVC-U samples (S3)
95
3.10
SEM micrograph of impact-fractured surface of S0
(Magnification 200x)
3.11
SEM micrograph of impact-fractured surface of S3
(Magnification 200x)
3.12
96
SEM micrograph of impact-fractured surface of S7
(Magnification 200x)
3.13
96
97
Effect of filler content on the impact strength of EFB-filled
composites (S9-S12) and EFB-filled acrylic-impact modified
composites (S13-S28)
3.14
98
Effect of filler content on the impact strength of EFB-filled
composites (S9-S12) and EFB-filled CPE-impact modified
composite (S29- S44)
3.15
SEM micrograph of the impact-fracture surface of composite
incorporated with 10 phr filler (Magnification 500x)
3.16
100
Polar-polar interaction between PVC molecule and
cellulose molecule.
3.20
100
SEM micrograph of the impact-fractured surface of composite
incorporated with 40 phr filler (Magnification 500x)
3.19
99
SEM micrograph of the impact-fractured surface of composite
incorporated with 30 phr filler (Magnification 500x)
3.18
99
SEM micrograph of the impact-fracture surface of composite
incorporated with 20 phr filler(Magnification 500x)
3.17
98
SEM micrograph of filler debonding on the impact-fractured
102
xx
surface of composite incorporated with 30 phr filler
(Magnification 900x)
3.21
103
SEM micrograph of filler bundles pulled-out area on the impactfractured surface composite incorporated with 30 phr filler of S11
(Magnification 1000x)
3.22
Effect of acrylic content on the impact strength of EFB-filled
acrylic-impact modified composites (S0-S4 and S9-S28).
3.23
104
105
Effect of CPE impact modifier content on the impact
strength of EFB-filled CPE-impact modified composites
(S5 -S8 and S29-S44)
3.24
Effect of acrylic and CPE impact modifier on the impact
strength of EFB-filled impact-modified composites
3.25
116
Effect of filler and CPE content on the flexural strength of
EFB-filled CPE-impact modified composites (S29 - S44)
3.35
116
Effect of filler and CPE content on the flexural modulus of
EFB-filled CPE-impact modified composites (S29 -S44)
3.34
115
Effect of filler and acrylic content on the flexural strength of
EFB-filled acrylic-impact modified composites (S13-S28)
3.33
113
Effect of filler and acrylic content on the flexural modulus of
EFB-filled acrylic-impact modified composites (S13-S28)
3.32
112
Effect of filler and CPE content on the flexural strength of
EFB-filled CPE-impact modified composites (S29-S44)
3.31
112
Effect of filler and CPE content on the flexural modulus of
EFB-filled CPE-impact modified composites (S29-S44)
3.30
111
Effect of filler and acrylic content on the flexural strength of
EFB-filled acrylic-impact modified composites (S9-S28)
3.29
109
Effect of filler and acrylic content on the flexural modulus
of EFB-filled acrylic-impact modified composites (S9-S28)
3.28
109
Effect of impact modifiers content on the flexural strength
of impact modified compounds (S0-S8).
3.27
107
Effect of impact modifiers content on the flexural modulus
of impact modified compounds (S0-S8)
3.26
105
Effect of acrylic and CPE impact modifier on the flexural
117
xxi
modulus of EFB-filled impact modified composites
3.36
Effect of acrylic and CPE impact modifier on the flexural
strength of EFB-filled impact modified composites
3.37
119
119
Effect of EFB filler and acrylic content on the impact strength
of EFB-filled acrylic-impact modified composites treated
with Prosil 9234 (S49-S68)
3.38
121
Effect of EFB filler and acrylic content on the impact strength
of EFB-filled acrylic-impact modified composites treated
with NZ 44 (S69-S88)
3.39
Bonding mechanism of NZ 44 coupling agent to
the filler’s surface
3.40
121
122
SEM micrographs of the impact fractured-surface of composites
(a) Prosil 9234 treatment (S51) (Magnification 100x) (b) S51
(Magnification 2000x) (c) NZ 44 treatment (S71)
(Magnification 500x) and (d) S71 (Magnification 2000x)
3.41
125
Effect of EFB filler and acrylic contents on the flexural modulus
of EFB-filled acrylic-impact modified composites treated with
Prosil 9234 (S9-S28 and S49-S68)
3. 42
127
Effect of EFB filler and acrylic contents on the flexural strength
of EFB-filled acrylic-impact modified composites treated with
Prosil 9234 (S9-S28 and S49-S68)
3.43
128
Effect of EFB filler and acrylic contents on the flexural modulus
of EFB-filled acrylic-impact modified composites treated with
NZ 44 (S9-S28 and S69-S88)
3.44
128
Effect of EFB filler and acrylic content on the flexural strength
of EFB-filled acrylic-impact modified composites treated with
NZ 44 (S9-S28 and S69-S88)
129
3.45
FTIR spectra of (a) PVC-U compound (S0) (b) composite (S11)
135
3.46
FTIR spectra of (a) filled composite (S11) (b) Prosil 9234-treated
filled composite (S51) (c) NZ 44-treated filled PVC-U
composite (S71).
3.47
Impact strength of unweathered and weathered impact modified
compounds
3.48
137
Impact strength of unweathered and weathered EFB filled
138
xxii
composites
3.49
Suggested reaction scheme for the accelerated photo-oxidation
degradation
3.50
155
Effects of EFB (S9-S12) and NPCC (S89-S91) on the flexural
modulus of composites
3.65
154
Effects of 10 phr NPCC, 20 phr NPCC, 3 phr acrylic and
3 phr CPE on the impact strength of EFB-filled composites
3.64
153
Effects of EFB filler and NPCC on the impact strength of
composites
3.63
152
FTIR spectra of unweathered and weathered-acrylic-impact
modified composites
3.62
152
FTIR spectra of (a) unweathered and (b) weathered-acrylic
impact modified composites
3.61
151
FTIR spectra of (a) unweathered and (b) weathered-EFB-filled
composites
3.60
149
FTIR spectra of (a) unweathered and (b) weathered PVC-U
compounds
3.59
148
Appearance of some samples surface before and after exposed
to UV irradiation for 504 hours
3.58
148
Flexural strength of unweathered and weathered EFB-filled
impact modified composites
3.57
147
Flexural modulus of unweathered and weathered EFB-filled
impact modified composites
3.56
147
Flexural strength of unweathered and weathered EFB-filled
composites
3.55
145
Flexural modulus of unweathered and weathered EFB-filled
PVC-U composites
3.54
145
Flexural strength of unweathered and weathered impact
modified compounds
3.53
143
Flexural modulus of unweathered and weathered impact
compounds
3.52
141
Impact strength of unweathered and weathered EFB-filled
impact modified PVC-U composites
3.51
140
Effects of EFB (S9-S12) and NPCC (S89-S91) on the flexural
156
xxiii
modulus of composites
3.66
Effects of 10 phr NPCC, 20 phr NPCC, 3 phr acrylic and
3 phr CPE on the flexural modulus of the EFB-filled composites
3.67
161
Effect of unextracted and extracted EFB filler on the flexural
strength of composites at filler content of 30 phr
3.71
160
Effect of unextracted and extracted EFB filler on the flexural
modulus of composites at filler content of 30 phr
3.70
159
Effect of unextracted and extracted EFB filler on the impact
strength of composites at filler content of 30 phr
3.69
158
Effects of 10 phr NPCC, 20 phr NPCC, 3 phr acrylic and
3 phr CPE on the flexural strength of the EFB-filled composites
3.68
157
162
Effects of impact modifier content on water absorption of
acrylic-impact modified (S1-S4) and CPE-impact modified
compounds (S5-S8)
3.72
Effect of EFB filler content on the water absorption of
unmodified and modified composites
3.73
164
Effect of coupling agents on the water absorption of treated
unmodified composites
3.74
163
165
Effect of coupling agents on the water absorption of treated
acrylic-impact modified composites
166
4.1
(a) TG and (b) DTG curves for neat components
179
4.2
DSC trace of EFB filler
181
4.3
(a) TG and (b) DTG curves of unmodified filled PVC-U
composites
184
4.4
Polar-polar interaction between H20 and PVC molecules
185
4.5
(a) TG and (b) DTG curves for EFB-filled CPE-impact
modified PVC-U composites
187
4.6
(a) TG and (b) DTG curves for EFB filled acrylic-impact PVC-U 188
4.7
Polar interaction between MMA and HCl
189
5.1
Rigid PVC fusion mechanism in the Torque Rheometer
193
5.2
Soxhlet extraction apparatus
197
5.3
A typical temperature and torque curves of PVC-U
compound (S0) blended in the Brabender Torque Rheometer
200
xxiv
5.4
A typical temperature and torque curves of EFB-filled PVC-U
composite (S0) blended in the Brabender Torque Rheometer
5.5
201
Postulated lubrication mechanism of among PVC micro-particles
flow units, EFB fillers and acrylic impact modifiers
5.6
217
Postulated lubrication mechanism of among PVC micro-particles
flow units, EFB fillers and CPE impact modifiers
218
5.6
FTIR spectra: a) EFB filler b) extracted EFB filler
220
5.7
FTIR spectra (a) solvents mixture condensate
(b) concentrated extract
221
5.8
Palm oil molecular structure
222
5.9
SEM Micrograph for EFB Filler (Magnification 3000x)
223
5.10
SEM micrograph for extracted EFB filler (Magnification 1000x)
6.1
223
o
Extrudates of S0, S3, S7, S9 and S21 at die temperature of 185 C,
and extrudate of S37 at die temperature of 190 oC
233
6.2
Shape difference between the die and extrudate
234
6.3
Filled extrudates of S37 at die temperature of 180 oC and 185 oC
and at constant screw speed of 60 rpm
6.4
235
Filled extrudate of S9 with air bubbles on surface
236
o
6.5
Filled extrudates of S10, S22 and S38 at die temperature of 195 C
6.6
A typical DSC thermogram of S0 at different processing
temperatures
6.7
6.8
237
239
A typical stress-strain graph of tensile for extrudates at 60 rpm
and 180 oC
253
Predicted yield stress values at 3 m/s for S0
257
xxv
LIST OF SYMBOLS
b
-
width
d
-
thickness
CPE
-
chlorinated polyethylene
EFB
-
oil palm empty fruit bunch
Ec
-
flexural modulus of composite
Ep
-
flexural modulus of polymer
Gf
-
shear modulus of filler
Gp
-
shear modulus of polymer
HDT
-
heat deflection temperature
k
-
Boltzmann’s constant
L
-
span
Mt
-
water absorption at time t
NPCC
-
nano-precipitated calcium carbonate
NZ 44
-
zirconate based coupling agent
Prosil 9234
-
silane based coupling agent
PVC-U
-
unplasticised poly (vinyl chloride)
S
-
sample
Tg
-
glass transition temperature
TG
-
thermogravimetric curve
DTG
-
differential thermogravimetric curve
v
-
velocity
Vf
-
volume of filler
Vp
-
volume pyknometer
Vw
-
volume of water
W
-
failure load
xxvi
Wadditives
-
weight fraction of additives
Wd
-
dry weight
Wf
-
weight fraction of filler
Wpvc
-
weight fraction of poly (vinyl chloride)
Ww
-
weight after immersed into water
∆H
-
activation energy
∆S
-
deflection increment
∆W
-
load increment
ε
-
strain rate
εc
-
elongation at break of composite
εp
-
elongation at break of polymer
φf
-
volume fraction of filler
φm
-
maximum packing fraction
γ
-
stress concentration factor
ν
-
activation volume
νp
-
Poisson’s ratio of polymer
ρadditives
-
density of additives
ρc
-
density of composite
ρf
-
density of filler
ρw
-
density of water
σc
-
strength of composite
σp
-
strength of polymer
σy
-
yield stress
ψ
-
reduced concentration term
CHAPTER 1
INTRODUCTION
1.1
Overview
Poly (vinyl chloride) has grown into one of the major thermoplastics material
since it was first produced in the 1930’s. More than one-half of the PVC produced is
used in the building industry (Mengeloglu, 2001). Because of its blending versatility
(ability to be modified through the introduction of various additives) and costeffectiveness, PVC is one of the most worldwide used thermoplastics and it plays an
important role in the plastic industry as a major component of composite
manufacturing (Wenguang and La Mantia, 1996).
Cost reduction is achieved when fillers are incorporated into the PVC matrix.
In addition to reducing cost, other typical reasons for using fillers are stiffness
enhancement and thermal properties alteration of vinyl products. Currently, the most
important fillers for PVC are inorganic materials such as glass fibre, calcium
carbonate, agalmatolite, talc (Saad et al., 1999; Wee, 2001; Pedro et al., 2001; Xie et
al., 2001). These fillers are high-density materials (Mengeloglu, 2001). While they
offer wide property changes in the composites, their use is not cost effective on a
volumetric basis (Titow and Lanham, 1975). In addition, these inorganic fillers cause
2
wear of equipment during processing. Therefore the use of natural fillers such as
wood has been suggested as an alternative to mineral materials (Nabi Saheb and Jog,
1999).
Interest in the use of natural fillers has grown during the last decade and most
of the natural fibres used in thermoplastics composites are derived from wood. The
use of natural fillers in USA plastic industry in 2000 was estimated 0.4 billion pounds
or 7 % (Gurram et al., 2002). In fact, industry experts believe that the demand for
natural fillers for plastics composite applications will grow at least six-fold in the next
5 to 7 years (Stokke, 2002). The rationale behind this interest is that the use of natural
fibres offers several benefits, including lower cost, less abrasiveness to equipment,
high specific properties such as higher specific modulus (modulus/specific gravity),
renewable nature and biodegradability (Nabi Saheb and Jog, 1999).
Even though natural fibres offer several advantages, certain drawbacks such as
incompatibility of fibre with the thermoplastics matrix, the tendency to form
aggregates, and poor resistance to moisture greatly reduce the potential of these fibres
to be used as reinforcement. All these drawbacks, especially incompatibility, lead to
low fibre-matrix interfacial bonding strength and poor wetting of the fibres by the
matrix resin, which can cause reduction in mechanical performance of the composites.
Therefore, surface modification by the use of coupling agents is commonly suggested
as solution to overcome the drawbacks of lowered strength property. These chemical
reagents convert the hydrophilic surface of cellulosic fibres to hydrophobic one. As a
result, the fibre-fibre hydrogen bonds is reduced and the adhesion is also improved via
the mechanism such as formation of chemical bonds between treated fibres and
polymer matrix (Xanthos, 1983; Raj et al., 1989, 1989, 1990; Maldas and Kokta,
1990,1990,1991; Myres et al., 1991; Maiti and Subbarao, 1991; Ahmad Fuad et al.,
1994,1997; Sivaneswaran, 2002; Baiardo et al., 2002; Fabbri et al., 2004).
One of the natural fillers that have been tried was oil palm empty fruit bunch
(EFB). EFB is one of the natural fillers obtained from oil palm. The incorporation of
3
EFB as a reinforcing component in the polymer composites has received much
attention (Sareekala et al., 1996/97; Rozman et al., 1998, 2001, 2001; Sarani et al.,
2001; Abdul Khalil et al., 2001). Most of the research works on EFB so far dealt with
polymers such as polypropylene, polyester, polystyrene and phenol-formaldehyde
resin. The researchers focused on the effect of filler loading, filler particle size
distributions and filler treatment on the mechanical properties of the composites. Like
other natural fillers, many issues have been identified in the processing of the
composites. These include low compatibility between EFB fibre and polymer matrix,
higher moisture intake, poor distribution of the fibre in the matrix and effect of oil
residue on mechanical properties.
Although EFB has been useful as fillers in various polymers mentioned above,
the use of EFB filler in PVC has not been studied extensively. Most of the researchers
have used wood flour, wood sawdust and rice husk ash as fillers in PVC matrix
(Matuana et al., 1998, 2001; Sivaneswaran, 2002; Sombatsompop et al., 2003). The
use of these fibres in the PVC matrix produces products that are more brittle than neat
PVC. The incorporation of the natural fibres alters the ductile mode of failure of the
matrix. The brittleness of PVC/wood fibre composite compared to the unfilled PVC
may prevent this emerging class of materials from capturing their full market potential
in applications such as door and window frames (Mengelollu, 2001).
One of the most important aspects in the development of PVC compound by
using fillers is to achieve a good combination of properties and processability at a
moderate cost. As far as mechanical properties are concerned, the main target is to
strike a balance of stiffness, strength and toughness (Mohd Ishak et al., 2000). The
incorporation of filler in thermoplastic such as PVC is associated with an
enhancement in stiffness and strength but a decrease in toughness. The incorporation
of impact modifiers in PVC, on the other hand will result in a significant
improvement in toughness at the expense of stiffness and strength.
4
The enhancement of impact properties of PVC-U by introduction of a rubbery
phase is a well-known phenomenon which has been widely exploited commercially.
Among those which have extensively used are chlorinated polyethylene (CPE) and
various modified acrylic. Hiltner et al. (1984) reported that CPE modifier formed a
network enclosing PVC primary particles in order to develop the desired impact
strength whereas Robinovic (1983) found that acrylic modifier formed a distinct
dispersed phase in the continuous PVC phase. The dispersed rubber particles of
acrylic were independent of the processing time and temperature, whereas the CPE
network structure was dependent of those factors.
The studies have concluded that the function of the impact modifiers (whether
in the form of discrete phase or network structure) was to increase the toughness of
PVC by facilitating the ability of PVC matrix to shear yield and/or craze. This means
that the PVC would deform rather than fracture when subjected to a sudden load
(Petrich, 1973; Lutz, 1993). Meanwhile, Stevenson (1995) has pointed out that the
impact modifiers can also be used to correct the detrimental effects of other additives
such as fillers by boosting the impact performance of the material.
1.2
Significance of Study
Based on the previous findings mentioned above, no study has been reported
on the use of EFB fibre in the PVC matrix. Most studies involved investigation of the
mechanical properties of natural fibre polymer composites in terms of natural fibre
content, various treatments of the fibre, whereas very few have investigated
processability and thermal stability of the composites. According to Sombatsompop et
al. (2003), the area for PVC/wood fibre composites are still actively pursued,
especially in areas of processability and thermal stability-related mechanical
properties of the composites.
5
With the rising environmental issues in the limelight and the need for new
applications of agricultural by-products such as EFB to be more useful in order to
minimize industrial waste, therefore agricultural by-products seem attractive enough
to be use as reinforcement filler alternative for filled thermoplastics composites. Since
oil palm has now become a major cash crop and is cultivated commercially in
Malaysia, many million tons of EFB on dry weight basis are produced annually
throughout the world. EFB is an agricultural waste, which is left unutilized after the
removal of the oil seeds for oil extraction. In order to minimize the abundance of this
waste and environmental problems, therefore new applications are urgently required
for EFB to be more useful (Sreekala et al., 1996/97). The utilization of this EFB as a
reinforcement in polymers has some economical as well as ecological importance.
PVC is basically a rigid thermoplastic. It is inherently ductile because of the
polarity and low-temperature molecular relaxation. However, it is brittle at high
deformation rate and under concentrated stress, and PVC is known as a notchsensitive polymer (Wimolmala et al., 2001). Previous studies have also shown that the
impact strength reduces drastically with addition of natural fillers (Nabi Saheb and
Jog, 1999; Mengeloglu, 2001). Impact modifier is therefore added to increase the
ductility and toughness of PVC. Although ductility increases, the impact modifier
used is costly and tends to decrease the PVC-U stiffness. In this study, the strategies
to use EFB fillers together with impact modifier in PVC-U are deliberately done to
develop PVC-U composites with good stiffness without sacrificing both desirable
toughness and cost effectiveness.
Therefore, in order to understand the properties of the newly developed of
PVC-U composites, the effects of filler and impact modifier contents, and filler
treatment on the mechanical and thermal properties, processability and extrusion
process on the PVC-U composites are investigated.
6
1.3
Objectives of Study
The main objective of the study is to produce EFB-filled PVC-U composites.
To achieve the objectives, the following stages have been carried out:
(a)
To determine the effect of EFB filler, acrylic and CPE content on the
impact strength and flexural properties of the compression moulded
composites. The influence of EFB filler, acrylic and CPE content on
the thermal properties such as heat deflection temperature, thermal
degradation temperature and glass transition temperature are also
investigated. In addition, composites accelerated weathering and water
absorption properties rare also determined.
(b)
To study the effect of silane (Prosil 9234) and zirconate (NZ 44)
coupling agents on the impact and flexural properties and water
absorption of the compression moulded composites. From this study,
the most suitable coupling agent is determined.
(c)
To determine the effect of EFB filler, acrylic and CPE content on the
fusion characteristics of PVC-U compounds. The effect of different
processing temperatures on the composites is also studied.
(d)
To determine the effect of processing temperatures and screw speeds
on the impact, tensile and flexural properties of extrudates. The
influence of processing temperatures on fusion level of extrudates is
also determined.
7
1.4
Outline of Thesis
Chapter 1 presents the overview of the previous research works that has been
conducted by other researchers who used either EFB fibres as reinforcement or PVC
as matrix in their studies. Both the advantages and disadvantages of natural fibres are
also reported as well as the role of impact modifier in the PVC. The significance of
the study, the objectives of study and the layout of research are presented.
Chapter 2 begins with some definitions and general feature properties of PVC.
Several theories on PVC such as impact modification and fusion mechanism, and the
function of additives are described. The definitions and categories of composites and
the properties of EFB filler are also described. Literature survey on PVC filled
composites is also reported, followed by reviews on the application of various
coupling agents and the application of EFB as a reinforcement filler or fibre in the
thermoplastics composites systems. Several theories that have been used to predict the
relative modulus of filled composites are also reviewed.
Chapter 3 mainly describes the effect of filler content, impact modifier content and
coupling agents on the impact strength, flexural properties and water absorption of
composites. The effect of filler content on the density of composites, the application
of models to predict the relative modulus, and the impact strength and flexural
properties of weathered composites are also described. The morphological studies on
the impact-fractured surface and the presence of functional groups on the samples
investigated using Scanning Electron Microscope (SEM) and Fourier Transform
Infra-Red (FTIR), respectively, are also reported.
Chapter 4 reports the thermal properties of the composites. A wide array of thermal
analysis techniques such as thermogravimetric analyser (TGA), heat deflection
temperature analyser (HDT) and differential scanning calorimetry (DSC) are used to
8
investigate the thermal degradation temperature, heat deflection temperature and glass
transition temperature, respectively.
Chapter 5 reports on the processability of PVC-U compounds. The effects of EFB
filler content, extracted EFB filler, CPE and acrylic impact modifier content and
mixing temperature are reported. The effect of extracted EFB filler content on the
processability is also investigated as a minor part of this study. FTIR is used to
identify the related functional groups present in the extractives and the changes in
EFB filler surface, followed by morphological study on the extracted EFB filler
surface using SEM.
Chapter 6 reports the effect of screw speed and processing temperature of extrusion
on the impact strength, flexural properties, tensile properties and fusion level of the
composites. The effect of crosshead speed on the tensile properties is studied to
predict the yield stress of extrudates. The fusion level of extrudates at different
temperatures is also investigated using DSC.
Chapter 7 presents the overall conclusions and suggestions for further work.
CHAPTER 2
LITERATURE REVIEW
2.1
Poly (vinyl chloride)
Poly (vinyl chloride) is the second largest of thermoplastics (polypropylene
being the first on the list) being used as raw material in the plastic industry. The world
market reported that the growth rate of the world production and the growth rate of
the world consumption of PVC thermoplastic from 1999 to 2005 would be 3.30 %
and 3.83 %, respectively (Murphy, 2001). It shows that although poly (vinyl chloride)
has been dubbed as a toxic material but its excellent properties and versatility cannot
be denied.
2.1.1 Definitions and General Feature Properties
Poly (vinyl chloride), commonly known as PVC, is a predominantly
amorphous polymer with a basic repeat unit [-CH2-CHCl-]. Based on its chemical
structure, PVC is structurally very similar to polyethylene (PE), with a chlorine atom
10
substituted for a hydrogen atom on alternating carbons in the chain. The number of
chlorine molecules attached to these components governs the overall characteristics of
PVC polymer or compound to a substantial extent (Penn, 1971).
The chlorine atom is many times larger than the hydrogen atom and greatly
reduces the ability of the molecules to rotate and flex. The base polymer is therefore
quite stiff and has low creep properties (long term deflection under stress) at room
temperature. Being highly electronegative, chlorine atoms create polarity and are
electrically repulsive to each other. This feature results in further immobility,
inflexibility and low level of crystallinity. Therefore, the impact resistance of the
basic vinyl chloride is quite poor but is relatively resistant to organic solvents and
flame.
The polarity of PVC is responsible for its remarkable ability to form
compatible compositions with many other polymers and plasticizers as well as other
formulating ingredients (Coaker and Wypart, 1993). These advantageous properties
offer rigid PVC the opportunity to be used as base polymer matrix for the reinforced
version. This can be explained by their characteristics as listed in Table 2.1. Its main
limitations are its low softening temperature (82 oC) and glass transition (80-84 oC)
and its tendency to degrade at elevated temperature.
Under heat or ultraviolet light, the chlorine atoms become unstable and break
out from the rest of the molecules. This heat sensitivity makes the base polymer
extremely difficult to be processed by conventional melt processes. However, due to
its affinity for additives, this undesirable property of PVC could be overcome by the
development of suitable stabilizer in the early 1930’s (Butters, 1982). Despite its poor
thermal stability, when correctly formulated, PVC is still widely used since it is
relatively cheap, inherently flame retardant, strong and stiff, and good chemical and
weathering resistance (Whelan and Goff, 1989).
11
Table 2.1: Some physical properties of moulding PVC products and compounds
(Titow, 1991)
Typical values or values range for
Rigid PVC
1.30-1.45
Properties
Density (gcm-3)
Tensile strength (MPa)
31-60
Elongation at break (%)
2-40
Flexural strength (MPa)
62-100
Young’s modulus (GPa)
a. in tension, E
2.5-3.5
b. in shear, G
1.0-1.8
c. in flexural, EB
2.0-3.5
d. in compression, E
2.2-3.5
Thermal conductivity (Wm-1K-1)
0.14-0.28
2.1.2 PVC Polymerisation
Commercial grade PVC is produced by two main routes as shown in Figure
2.1. The vinyl chloride monomer used in production of PVC is produced either by
direct hydrochlorination of acetylene or by chlorination of ethylene.
Process 1.
CH ≡ CH
Acetylene
+
HCl
→ CH2=CHCl
Hydrochloric
acid
Vinyl chloride
monomer
12
Process 2
CH2=CH2
+
Ethylene
CH2Cl-CH2Cl
1,2-dichloroethane
Figure 2.1
Cl2
Chlorine
→ CH2Cl-CH2Cl
1,2-dichloroethane
⎯⎯
⎯
⎯→
pyrolisis
CH2=CHCl
Vinyl chloride
monomer
+ HCl
Hydrochloric
acid
The chemistry of vinyl chloride monomer production
PVC resins are normally produced by polymerisation procedure (Penn, 1971).
Three of these essential polymerisation procedures are, in terms of commercial
importance: (1) suspension polymerisation (about 80 % of the commercial
production) (2) emulsion (about 10-15 %) and (3) bulk or mass and solution
polymerisation (about 10 %).
The majority of PVC is produced via the suspension technique due to the fact
that PVC produced by this technique forms the basic compound intended for
extrusion or moulding. For suspension resins, vinyl chlorides are dispersed in the
aqueous phase to form a dispersion of droplets. The polymerisation takes place within
the droplet until the required conversion of monomer to polymer is achieved. The
PVC resins normally have a compact, relatively non-porous closed structure.
In the emulsion polymerisation, the vinyl monomer is emulsified in water,
which contains water-soluble catalyst and is characterized by high polymerisation
rates leading to high-molecular weight resins. This type of PVC is normally less
expensive than other forms of PVC, but requires higher amount of lubricants to assure
the glossy surface of the finished commodity products. Bulk polymerization resins are
snowball-like particles having very porous structure with a large surface area.
Because of this, bulk PVC resins are much easier to fuse into homogeneous melt.
13
The suspension and mass polymerisation processes both produce a particulate
with a mean particle size in the range 100-150 µm. Meanwhile, emulsion
polymerisation produces a product in the latex form with very small and narrow
particle size distribution of the order 0.1 to 2 µm. However, all PVC resins have a
series of particulate-sub structures.
Commercial
PVC
materials
are
often
classified
according
to
the
polymerisation method and the molecular weight. The molecular weight of PVC is
often quoted in terms of a K-value instead of the actual molecular weight. It is the
measurement of the viscosity of dilute solution. The higher molecular weight in
general is indicated by the increase difficulty in processing. In commercial resins, the
number average molecular weight lies in the range of 50,000 to 100,000 (Sarvetnick,
1969).
2.1.3 Morphology of PVC
The PVC resin particle is unusual in structure and to understand the properties
and processing of this unique polymer requires an understanding of its structure or
morphology. Suspension PVC resin particles usually posses a pericellular “skin” or
“membrane” which extends almost continuously over the entire outer surface of the
grain. This skin is formed during the early stages of polymerisation.
Suspension-polymerised PVC in a powder form possesses various level of
morphology. Powder particles, which are visible to the naked eyes, are known as
grains. Each grain is an assembly of primary particles, which are loosely packed
14
together. Each primary particle appears to be made up of smaller structure called
domains. These are illustrated in Figure 2.2 (Hattori et al., 1972).
Domain
10-30 nm
Colloidal
Skin
Primary Particle
0.2-1.5 µm
Grain
65-150 µm
Figure 2.2
PVC particle morphology (Gilbert, 1985)
There are arguments among researchers in defining the terminology to
describe PVC particle morphology. Thus, to avoid confusion and to maintain
consistency of the PVC terminology, a table with a standard terminology was
summarized and published by Geil (1977). This standard PVC nomenclature is listed
in Table 2.2 and it will be used for further discussion on the morphology.
Although PVC is an amorphous polymer, it has been reported that it contains
about 5-10 % of crystallinity (Soni et al., 1982 and Gilbert, 1985). Based on small
angle X-ray scattering (SAXS) data, the crystalline structure has been proved by the
existence of crystalline noduli with the size of 2.7 nm and d-spacing of 10 nm for
virgin PVC. This crystalline nucleus which was surrounded by constrained
amorphous has been associated with the basic micro-domain structure of PVC.
15
Table 2.2: PVC nomenclatures (Geil, 1977)
Term
Grain
Range
(µm)
50-250
Average
(µm)
130
Description
Visible constituents of free flowing
powders, made up of more than 1
monomer droplet
Sub-grain
Agglomerate
10-150
40
Polymerised monomer droplet
2-10
5
Formed during early stage of
polymerisation by coalescence of
primary particles (1-2 µm). Grows
with conversion to size shown.
Primary particle
0.6-0.8
0.7
Grows from domain. Formed at low
conversion (less than 2 %) by
coalescence of micro-domain: grows
with conversion to size shown.
Domain
0.1-0.2
0.2
Nucleus of primary particle. Only
observed at low conversion (less than
2 %) or after mechanical working. It
becomes primary particle as soon as
growth starts.
Micro-domain
0.01-0.02
~0.02
Smallest species so far identified.
Aggregate of polymer chains.
Summers (1981) studied the nature of crystallinity of PVC and found that the
crystallites in the micro-domain structures were connected by tie molecules with a
•
100 A spacing. These crystallites acted as crosslinks in a three-dimensional network
which prevented primary particles interaction at low temperature. However, at high
temperature (177 oC) some of the crystallite melted and recrystallization after cooling
led to strong ties between the primary particles. It was also revealed that PVC
contained two types of crystallinity: primary crystallinity, which was formed during
polymerisation and secondary crystallinity formed during recrystallization (Lacatus
and Rogers, 1986).
16
2.1.4 PVC Fusion
PVC must undergo fusion in every fabrication process in order to achieve its
best mechanical properties. It is generally agreed by researchers that the level of
fusion has significant influence on the mechanical, physical and chemical properties
of the PVC. To obtain optimum properties an appropriate level of fusion is needed
(Covas et al., 1988)
The fusion process for PVC is the subject of great deal of discussion, and there
are many views about the exact courses of this process. Although there are several
ideas suggested by the researchers, but one conclusion to describe the fusion process
of PVC can be made, namely the fusion process is the breakdown process of the PVC
grains and is affected by a combination of such external parameters such as
temperature, pressure and shear. The methods used to break down the PVC grains,
whether via Brabender torque rheometer, two roll mill, single screw extruder or twin
screw extruder, results in the different breakdown mechanisms (Benjamin,1980;
Parey and Manges, 1981; Portingell, 1982).
Benjamin (1980) defined that the fusion of PVC as the process of removing
the boundaries between base particles whereby a continuous mass that resulted have a
homogeneous molecular structure. The grains have broken down to the so-called
primary particles. Further broken down of the primary particles to the sub-primary
particles took place if sufficient energy was applied. The structure of these subprimary particles was said to be a continuous network of molecular chains, which to
some extent, was bound together by a crystalline nucleus. The sub-primary particles
contain approximately 10 % crystalline material.
Parey and Manges (1981) concluded that the fusion of PVC proceeds in two
stages. In the first stage, the PVC dry-blend was changed into a material capable of
fusing under the influence of temperature and particularly of shear. In the second
17
stage, mainly through the effect of temperature, this material becomes fused. The
shear here, only served to homogenize the material. Meanwhile, Portingell (1982) has
defined fusion process is a destruction process of grains and primary particles and the
establishment of an entanglement network locked by a network of crystallites. This
destruction process is accomplished by the combined action of heat, pressure and
shear during processing. The extent of destruction of particulate of PVC is known as
the degree of fusion.
2.1.4.1 Mechanisms of Fusion
There are two mechanisms of PVC fusion as suggested by Allsopp (1982), and
these are illustrated in Figure 2.3. If the condition such that shear is applied before
densification is complete, such as Banbury mixer and Brabender mixing, grain
comminution results, but if grain densification is complete before shear force is
applied, such as extrusion, two roll milling, and compression moulding, then
compaction-densification-fusion-elongation (CDFE) mechanism results. The route
CDFE mechanism occurs at less shear-intensive processing conditions. The
mechanism has been proposed by Allsopp (1982). The route of CDFE is illustrated in
Figure 2.3.
As the material progresses in the screw, the grains are compacted together and
simultaneously eliminate the internal porosity of the grains. Further along the screw
the PVC grains start to show a high level of densification, with the additives deposited
in pockets around the grain surface. Midway along the screw, grain densification is
complete, with almost complete fusion of the grains, but the additives still remain
concentrated at the grain surface. Between the end of the screw and the form side of
the breaker plate, the grains become highly elongated and homogenisation of PVC
and additives becomes very good. The mechanism is generally similar with the works
reported by other researchers which confirmed that in extrusion, the main route for
fusion was through the deformation of grains by low shear (Gilbert et al., 1983; Covas
et al., 1988). They also suggested the overall view of fusion by postulating a melting
18
and recrystallizing process leading to network formation at the latter stages of the
process.
Figure 2.3
Mechanism of fusion during processing extruder (Allsopp, 1982)
The route of fusion by comminution mechanism occurs in the shear intensive
processing conditions. Allsopp (1982) suggested that a PVC fusion mechanism for a
torque rheometer as shown in Figure 2.3 where the original PVC grains underwent
comminution and formation of agglomerates, which consisted of bound fragments of
comminuted grains. When densification of primary particles occurred, the additives
were well dispersed throughout the matrix. With further densification, the primary
particles structure could still be observed and finally the boundaries between primary
particles disappeared, the particles lost their identity, and a three-dimensional
entanglement network of polymer chains was formed and the additives were
uniformly distributed. There were crystalline regions inside the primary particles,
which were connected together by molecules forming a network structure (Krzewki
and Collins, 1981). Similar fusion mechanism was also described by Benjamin (1980)
who divided the mechanism into two distinct phases as shown in Figure 2.4.
19
Phase 1: The PVC grain broke down into primary particles. The molecular
network remained within the boundaries of the particles although the primary
particles underwent the compaction.
Phase 2: With the continuation of the process, further breakdown of the
primary particles occurred and followed by the formation of a continuous molecular
network of entanglement.
Figure 2.4
Schematic presentation of fusion process for PVC (Benjamin, 1980)
2.1.4.2 Fusion Level Assessment: Differential Scanning Calorimetry
Assessment of the state of fusion is of utmost importance in order to achieve
satisfactory product properties.
Methods presently employed include acetone
immersion, zero length die extrusion, and calorimetry (Butters, 1982). Recent
20
investigations (Gilbert and Vyvoda, 1981; Teh et al., 1989) indicated that thermal
analysis being the simplest and most effective quantitative method for obtaining a
considerable amount of information about the fusion of processed PVC compounds.
Differential Scanning Calorimetry (DSC) approach to quantify fusion as
defined in the previous studies involves detecting two endotherm peaks, A and B as
shown in Figure 2.5 (Gilbert and Vyvoda, 1981; Teh et al., 1989). The first an
endothermic baseline shift before two endotherms, corresponded to the glass
transition temperature (Tg) of the rigid PVC. Gilbert (1985) reported that Tg of PVC
was largely unchanged (except for plasticized compounds) with the heat treatment or
processing but not for the two endotherm peaks.
ENDO
∆T
EXO
Moulding
Temperature
Temperature oC
Figure 2.5
DuPont thermal analysis of PVC-U compound compression moulded
at different temperatures
Peak B represents the melting of crystallites, which decreased in size and
shifted to higher temperature as the processing temperature increased.
The size
decrease was attributed to the melting of less perfect or smaller crystallites, whilst the
21
temperature shift was caused by annealing of unmelted crystallites. Other additional
useful information is available from position of peak B where the B onset temperature
is equal to the maximum processing temperature reached by the polymer sample.
Peak A increased in size as the processing temperature increased. The area of
A, however, is not yet fully understood but is probably be related to the degree of
fusion. The nature of endotherm of A probably corresponds to the formation of
imperfect ordered regions which is produced as a continuous PVC network develops,
and which subsequently melt upon reheating.
The heat of fusion of endotherms was used by researchers to analyse the
degree of fusion of PVC compounds. The heat of fusion of the first endotherm, A has
been employed by Gilbert and Vyvoda (1981) to asses the degree of fusion but Teh et
al. (1989), reported that a more convenient normalized form where the ratio of the
heats of fusion of endotherm A to the sum of the endotherms A and B was used. The
similar method was also used by Cora et al. (1999) to determine the relationship
between impact strength and morphology in PVC window profiles with fusion level.
2.1.4.3 Interrelation between Fusion and Properties
Benjamin (1980) extruded a series of pipes under controlled conditions to
provide four fusion levels. Tensile results (stress at yield) suggested a constant
maximum value at a higher fusion level of 68 %, while ductility tests, such as tensile
impact, tensile strain at break, resistance to crack formation, produced an optimum
value at approximately 44-68 % fusion level. Benjamin concluded that a fusion level
of approximately 60-70 % would provide the best balance of properties for particular
pipe and composition chosen. This corresponds to some primary particle still
remaining within the network morphology.
22
Covas et al. (1988, 1992) provide a correlation between processing, structure
and properties. This processing study considered both a single and a twin screw
extruders, and a mechanism of fusion was conjectured based upon the Allsopp (1982).
Tensile properties were evaluated by producing families of stress-strain curves with
different fusion level at different test rates and test temperatures. Yield properties
were, again, seen to be unaffected by fusion level and were attributed to molecular
relaxation mechanism, however elongation at break and stress at break were
dependent upon fusion level.
A maximum value of impact strength occurred between fusion levels 40-65 %
as observed by Benjamin (1980). This fusion range corresponds to a processing
temperature of 193-203 oC and the optimum network morphology with possible
residual primary particles. Similar reason was related to the impact performance,
where the maximum was achieved for the maximum levels in the range 69-70 %,
which was also reported by other workers (Marshall et al., 1983; Gilbert, 1985). The
reason for the decrease in impact strength after reaching the maximum value was not
fully understood, but it seemed to occur when primary particles have disappeared to
produce a reasonably homogeneous matrix. Meanwhile the maximum value was
possibly due to the presence of a new network structure and some primary particles
were beneficial in providing a mechanism for stress distribution.
Uitenham and Geil (1981) and Terselius and Jansson (1984) have studied the
relationship between tensile properties of the extrudates and level of fusion for rigid
PVC and found that the yield parameters were not sensitive to variation in the degree
of fusion. Information on this relationship has shown that yield stress at low strain
rate was independent of the relative coherence of the entanglement network and
number of crystalline junctions, and it was probably related to molecular relaxation
processes.
Terselius et al. (1981,1984,1985) also, published a number of papers, which
discussed the effect of fusion levels on pipe properties. The effect of mass
23
temperature of 176 oC-205 oC at extrusion on the impact strength of specimens from
pipe was studied. Falling weight tests have clearly demonstrated the existence of a
maximum in impact strength at a moderate mass temperature (190 oC) of extruded
pipes (unnotched). It was explained by increased post-yield deformation, presumably
due to voiding and local yielding in the interparticular weak regions of specimens of
reduced entanglement density. Charpy test on notched specimens showed a marked
increase of impact strength at moderate mass temperature (fusion level). This was
attributed to improved strength and coherence of the entanglement network, and thus
increased the resistance to crack propagation.
Summers et al. (1982) who studied the dropped dart impact strength of
extruded specimens found that toughness went through a maximum then decreased
with increased melt temperature and increased degree of fusion. This is similar to the
observations made by Benjamin (1980) and Terselius et al. (1985). In contrary with
the previous findings, Summers et al. (1982) explained that the loss of impact strength
at high extrusion temperatures was due to lubricant failure and melt fracture (as
discussed in lubricant section)
Cora et al. (1999) provide a recent correlation between impact strength and
morphology in poly (vinyl chloride) window profiles with fusion level. In this study,
the toughness of extruded PVC window profiles not only depended on intrinsic
variables such as type and level of impact modifier, filler and lubricants but for a
given impact test (i.e. given stress and strain rate), toughness was also greatly affected
by the free volume within the matrix, an extrinsic variable. Free volume for a given
formulation is determined by the degree of fusion the matrix (crystallinity). As melt
temperature increases the three-dimensional crystalline network fuses, leading to
glassy state with lower free volume. This increased the stress at yield and
subsequently reduced toughness of the materials. This study contradicted with the
results obtained by other researchers (Uitenham and Geil, 1981; Terselius et al., 1984,
1985; Covas et al., 1988, 1992).
24
2.2
PVC and Additives
Even though PVC polymer resins have been reported to possess many
attractive advantages with vast commercial demands, some imperfections in virgin
PVC such as susceptibility to heat degradation, relatively high melt viscosity,
comparably low heat deflection temperature, limited strength and stiffness. To
counteract these imperfections and to extend its range of applications some
modifications are required within original PVC materials such as adding small
amounts of additives such as heat or thermal stabilizer, lubricants, processing aids,
pigment, impact modifier, and so forth.
2.2.1 Heat Stabilizer
PVC is thermally unstable and degrades rapidly at normal processing
temperatures unless stabilized. Thermal stability of PVC has been reported in detail
by Wypych (1985). It has been well documented that PVC undergoes
dehydrochlorination at its normal processing temperatures (180-200 oC) or upon long
term exposure to ultraviolet light. As shown in Figure 2.6, the dehydrochlorination
reaction proceeds like a chain reaction, producing long sections of conjugated
polyenes. The process of heat degradation liberates hydrogen chloride (HCl), which
has an autocatalytic effect on the degradation. Many stabilizers act primarily by
reaction with hydrogen chloride to inhibit the hydrogen chloride from accelerating the
process of thermal degradation. Therefore, the heat or thermal stabiliser such as metal
carboxylates and organotin compounds added to the PVC compound, usually posses
two major roles: scavenging HCl and reacting with the polymer to prevent HCl loss
and simultaneous discoloration.
25
HC
CH
CH2
CH
Cl
CH
CH2
Cl
CH
Cl
-H C l
HC
CH
H
C
C
H
CH
CH2
Cl
CH
Cl
-H C l
HC
CH
C
H
H
C
C
H
CH
CH
Cl
Figure 2.6
Zip-elimination of HCl from PVC and simultaneous formation of
sequences containing conjugated double bonds (polyenes) in the chain during
degradation (Wypych, 1985)
The effectiveness of stabilisation depends on the capability of the stabiliser to
mitigate or alter the degradation and to disrupt the chain reactions already started. The
principal phenomena symptomatic involved in the thermal degradation of PVC those
react with stabiliser are listed below (Wypych, 1985):
•
Dehydrochlorination of the chains through the elimination of HCl. The
presence of HCl is to promote further dehydrochlorination, and consequent
degradation, sometimes referred to as an ‘unzipping mechanism.’
•
Formation of double bonds, which are conjugated in the polyene sequences.
They are responsible for the development of colour. The polyenes are active in
secondary reactions leading to crosslinking and the formation of aromatic
pyrolysates.
26
•
The presence of tertiary chlorine atoms (chlorine on branch carbons) and end
groups in the PVC chain. The tertiary chlorine atoms are particularly heatlabile and they are responsible for the initiation of evolution of HCl and the
formation of double bonds. Decomposition can also be initiated at the end
groups.
2.2.2 Lubricants
According to Marshall et al. (1969), lubricant, in general, can be defined as a
chemical compound necessary for minimisation of shearing forces during processing.
During processing, lubricants firstly coat the PVC granules and then, with continued
heating soften the PVC as they become soluble in the polymer. The granules are
forced together by processing and coalesce to give a state of fusion, such that, the
more soluble the lubricant, the more readily fusion takes place. In addition the
metal/polymer adhesion is reduced and surface slip increases. For that reason,
processing lubricants are widely used to assist the passage of the polymer melts
through the processing machinery.
Depending on the lubricating action and effects, lubricants are usually
classified into two categories, internal and external lubricants. Internal lubricant is
highly compatible with PVC to promote a breakdown of the PVC resin granules to the
primary particles at processing temperature of about 160 oC and influences flow
through reduction in the bulk viscosity of the melt or reduction of the chain-chain
intermolecular forces. The fatty esters, metal stearates (calcium stearate) or alcohol
are typical types of this lubricant (Bower, 1986). Meanwhile, external lubricant is
incompatible or less compatible (compared to internal lubricant) at all temperatures
with the PVC, and therefore during processing it migrates to the melt-metal interface,
promoting some effective slippage of the melt by reducing interfacial layer viscosity.
It also prevents the sticking of PVC to the processing equipment and improves the
27
surface finish of the product. The examples of this type of lubricant are metal soaps,
amide waxes and hydrocarbon waxes. Mostly, external lubricants delay the fusion of
the PVC compound, and internal lubricants speed up the fusion time or have very
little effect on it. In actual applications, however, lubrications do not always abide by
the rules (Chen and Lo, 1999).
The effect of lubricants on the fusion process or processability of PVC has
been studied extensively and particular attention has been given to the combination of
calcium stearate with a paraffin wax. Based on this combination, Rabinovitch et al.
(1984) has proposed a model of PVC lubrication of rigid PVC, as shown in Figure
2.7.
As suggested by Figure 2.7, fusion between the primary particles of PVC
without lubricants took place when three-dimensional crystallite networks within the
primary particles started melting, thus releasing polymer chain ends and loops for
partial interdiffusion across the original primary particle boundaries. Because of the
polarity, PVC attracted and stuck to the polar metal surface of processing equipment.
When calcium stearate was added to PVC (Figure 2.7b), the polar ends of its
molecules (CaCOOC-group) adhered not only to the polar PVC but also to the polar
metal surface, leaving the non polar (CH2)16CH3 to do the lubricating to displace PVC
melt from the metal surface, preventing it from sticking and providing limited slip
between the metal and PVC melt surfaces.
When paraffin wax was added to PVC (Figure 2.7c), it did not wet the metal
surface because it was a non-polar hydrocarbon, and therefore did not displace the
more polar PVC. Thus, in the presence of only paraffin wax, PVC stuck to the metal
surface.
28
When calcium stearate and paraffin were used together (Figure 2.7d),
interaction between the non-polar adjacent calcium stearate molecules is hindered by
the intervening presence of mobile non-polar alkane paraffin wax molecules which
were not attracted to the polar groups of calcium stearate, nor to PVC, nor to the metal
surface, but were weakly attracted to themselves and the non-polar hydrocarbons of
calcium sterate molecules. This mechanism led to the formation of a mobile layer,
which increased the separation between the thin calcium stearate films on the metal
surface, and on the PVC melt surface. It also provided a more mobile interface
between the calcium sterate molecules adhered to adjacent PVC primary particles.
Based on this mechanism and synergistic effect, it was concluded that the paraffin
wax delayed the fusion, while calcium stearate mildly promoted fusion. The similar
effect has also been found by Bower (1986).
Summers et al. (1982), have reported that at very high processing
temperatures (above 200 oC) where the PVC was substantially fused, the calcium
sterate/paraffin wax failed to perform well. Melt fracture took place, leading to a
brittle product. It is believed that, above 200 oC, the crystalline structure almost
disappeared and PVC became a continuous phase with the insoluble calcium
stearate/paraffin wax lubricants coalescing to form droplets rather than surrounding
individual primary particles flow units. The droplets of calcium stearate/paraffin wax
lubricant initiated melt fracture mostly at the surface, which led to surface roughness
and brittleness.
29
Figure 2.7
A model of PVC lubrication (not to scale) showing metal lubrication
and lubrication between PVC primary particle flow units for (a) no lubricant
(b) calcium stearate (c) for paraffin and (d) calcium stearate and paraffin
(Rabinovitch et al., 1984)
According to Krzewki and Collins (1981), calcium stearate has shown to
facilitate or delay the fusion process in the compound. Increased calcium sterate
levels in compounds with wax enhanced the fusion process whereas increased
calcium stearate levels without wax decreased fusion process at relatively low
temperatures but accelerate fusion at higher temperatures. With increasing
30
temperature, calcium stearate began to play a main role due to its increased solubility
in the polymer matrix and was capable to facilitate interdifussion of polymer chains
across the microparticle and submicroparticle boundaries to increase the rate of
fusion. They also found that the paraffinic wax delayed the resin particle breakdown.
Currently, Chen et al. (1995, 1999) investigated the fusion characteristics and
morphology of rigid PVC compounds using Haake torque rheometer. They used
oxidized polyethylene (OPE), calcium stearate (CaSt) and paraffin wax as lubricants
and CPE as impact modifier in the PVC compounds. Similar to Rabinovitch’s theory
of lubrication, the postulated mechanism of this PVC blend is given in Figure 2.8. The
fusion time of PVC/OPE compounds was the longest among other PVC blends. This
was attributed to a mobile layer, resulting from synergistic combined lubrication
between OPE and CaSt, which increased the separation and slipping among particles
(Figure 2.8e). Meanwhile, the fusion time of PVC/CPE/OPE compounds was the
shortest among other PVC blends. The interaction between OPE and CPE formed a
powerful,viscous material and appeared to act as a glue, which enabled the PVC
particles to fuse together easily.
31
Figure 2.8
Lubrication mechanism, showing metal lubrication and lubrication
between PVC microparticles flow units of PVC/CPE, PVC/OPE and PVC/CPE/OPE
compounds (Chen and Lo, 1999)
32
2.2.3 Processing Aid
Processing aids are used in PVC formulations for many reasons, but they can
all be grouped into two general categories of effects (Dunkelberger et al., 1993). Any
proposed mechanism for the action of processing aids must consider these two
different categories.
•
They accelerate and control the fusion process in PVC compound.
•
They strongly affect the rheological characteristic of the fully fused
PVC melt. The melt rheology can be further divided into four groups,
i.e. promotes homogeneous melt, increase melt strength, increases melt
viscosity and controls die swell.
The processing aid mechanism for promoting the fusion is still not well
understood. Bohme (1975) proposed that the processing aids promoted friction
between hot processing surfaces and the PVC compound during the fusion process.
Menges and Berndtsen (1976) argued that the processing aids became part of the
interstitial putty that initially bound the particles together and thus promoted the
fusion process. Krzewki and Collins (1981) proposed a combination of particleparticle and particle-metal friction processes as the role of the processing aids. These
previous findings, in general, elucidated that processing aids generated frictional heats
and improved the heat transfer throughout the system during processing.
Casey and Okano (1986) used acrylic processing aid to investigate the
rheological characteristic of PVC. They suggested a generally accepted theory to
explain the function of processing aids. The performance of processing aids is due to
their high affinity for PVC, and their very high molecular weights. These
characteristics form a rubber-like elasticity by the entanglement of processing aids
molecules with PVC. The processing aid is thought to melt first and causes the PVC
to become a tacky mass. The long chain of the processing aid increases the viscosity
33
of this mass (melt viscosity), causing a heat build up from the processing shear. The
resulting PVC is fully melted and homogeneous before it exits the processing
equipment. A homogeneous melt is one where there is minimum amount of primary
particles present to minimize melt fracture (increase melt strength) and shark skin
effects.
Pfening and Dunkelberger (1986) studied the effect of processing aids on PVC
die swell. The die swell behaviour of PVC melts is a manifestation of elastic
properties of the polymer melt. They reported that the addition of high molecular
weight acrylic processing aids to PVC provided better die swell control. The die
swell, including melt strength and melt elasticity increased with increasing molecular
weight of the processing aid (Casey and Okano, 1986). Hence, the knowledge of
molecular weight variables of processing aids is important for controlling the die
swell.
Sombatsompop and Phromchirasuk (2004) studied the effect of acrylic-based
processing aids on processability, rheology, thermal and structural stability and
mechanical properties of PVC/wood sawdust composites. They found that the
addition of acrylic-based processing aids into composites improved the thermal and
structural stability composites, which were
evidenced by an increase in glass
transition and decomposition temperature and a decrease in polyene sequences,
respectively. The changes in the mechanical properties of the composites involved a
composite homogeneity, which was varied by degree of PVC entanglement and the
presence of wood.
There are several types of acrylic-based processing aids and they are highly
compatible with PVC. They are methyl methacrylate-ethylacrylate (MMA-EA),
methacrylate-butyl acrylate (MMA-BA), methylmethacrylates-butyl acrylate-styrene
(MMA-BA-ST) (Dunkelberger et al., 1993).
34
2.2.4 Pigment
Photo-oxidation is an oxidation process of the polymers initiated by ultraviolet
(UV) radiation in the presence of oxygen and/or water. The oxidation of the polymer
chain occurs preferably in the polyene sequences and reduces their length, resulting in
a reduction or even elimination of colour. Besides that, oxidation process leads to
scission of the polymer chain and intermolecular crosslinking. Intermolecular
crosslinking causes material embrittlement (Gardiner et al., 1997).
In order to achieve long-term weatherability of PVC products, degradation
process must be avoided. A number of different pigments may be added to PVC-U
but the most commonly used pigment for outdoors applications is inorganic pigment,
namely titanium dioxide (TiO2). This pigment is extremely efficient in scattering the
visible light and in absorbing some ultraviolet light down to 300 nm. Sunlight in the
300-320 nm regions is reported to be most effective in initiating the degradation of
PVC (Mathur and Vanderheiden, 1982).
According to Mathew (1993), TiO2 pigment is readily dispersible and has
good chemical stability and hiding power. Besides that, the most important property
of TiO2 is its light scattering power for visible light. Hence, its use as a white
pigment, and its ability to absorb UV radiation and protect underlying layers, depends
on the amount of TiO2 present.
Matuana et al. (2001) investigated the photo-degradation and stabilization of
rigid PVC/wood fibre composites exposed to the accelerated UV weathering tests.
The experimental results indicated that wood fibres were effective sensitizers and that
their incorporation into a rigid PVC matrix had a deleterious effect on the ability of
the matrix to resist degradation caused by UV irradiation. The light stability of these
composites has improved quite efficiently with the addition of rutile (less photoactive
pigment) TiO2 during formulation.
35
2.2.5 Impact Modifier
Impact modifier is a semi-compatible rubbery polymer, which is dispersed as
small discrete domains in the rigid matrix to increase ductility and impact strength
(Lutz, 1993). Impact resistance is defined as the ability of a material to withstand the
application of the sudden load without failure. The polymer with good impact strength
is the polymer that has ability to yield or craze before failure.
The enhancement of impact strength of PVC through the introduction of
impact modifier has been recognized, mainly to compensate for the detrimental
effects of other additives on impact resistance. The detrimental effects occur when the
additives used to replace the volume fraction of polymer cannot dissipate stress
through the mechanisms known as shear yielding or crazing. Furthermore, certain
additives are miscible in the polymer matrix and restricting the mobility of polymer
molecules, which allow them to shear yield. Impact modifier is capable of improving
the impact resistance of the plastic by facilitating the ability of polymer matrix to
shear yield and/or craze (Stevenson, 1995).
Lutz (1993) has classified impact modifiers into three classifications:
•
Predefined elastomers (PDE) impact modifiers, which have constant
ultimate particle size and shape modifiers, are sometimes called discrete
particle modifiers (DPM). Usually, PDE modifiers have a rubbery core
surrounded by a shell of higher glass transitions temperature (Stevenson,
1995). While the rubber is responsible for the impact-modifying performance
of the additive, the shell has also important functions: it enables the additive to
be isolated as fine free-flowing powders, it facilitates dispersion of the
additive into the PVC matrix, and it interacts with the matrix to couple the
additive to the matrix.
Currently, the major modifiers of this type are
methacrylate butadiene styrene (MBS), all-acrylic (ACR) and modified acrylic
(MACR).
36
•
Non-predefined (NPDE) particles size and shape modifiers. They can
also be classified as network polymers (NM). It means that these modifiers
must form the network structures enclosing PVC primary particles at the
temperature typically in range of 150 – 200 oC in order to develop the desired
impact strength (McGill and Wittstock, 1983). The major modifiers in type II
are chlorinated polyethylene (CPE) and ethylene vinyl acetate (EVA).
Increasing the chlorine content of CPE or the vinyl acetate content of EVA
can attain higher degree of compatibility of these modifiers with PVC, and in
this case they act as plasticisers rather than impact modifiers. Besides that,
because of their inherent solubility in PVC, type II modifiers assume varying
morphologies in PVC melt depending on the conditions of temperature, time
and shear rates encountered in processing.
•
Transitional modifiers, due to their properties between the PDE and
NPDE. These modifiers are crosslinked rubber/elastomer moiety (compound)
and are sensitive to processing conditions. Acrylonitrile butadiene styrene
(ABS) terpolymer is categorized in this type of modifier. By varying the ratio
of ABS, a wide variety of impact, modulus and clarity properties in PVC can
be obtained.
Stevenson (1995) reported that one of the major functions of impact modifier
is to act as stress concentrators located throughout of the polymer matrix. The stress
concentrations occur in the polymer matrix around an impact modifier particle upon
application of a tensile stress to the material. The tensile stress is amplified in the
region surrounding the equator and is decayed rapidly to the level of the applied stress
as the distance from the modifier particle increases. The stress also changes quickly
as one moves from equator toward the poles of the modifier particle and is greatly
reduced from the applied stress near the poles. This stress distribution is illustrated in
Figure 2.9.
37
The localized concentrations of the stress when dispersed through the polymer
matrix provide multiple sites at which shear yielding and/or crazing of the polymer
can initiate simultaneously upon impact. The result is a structure with a large number
of small crazes and/or shears bands instead of a structure with a small number of large
crazes or shear bands that is more prone to failure.
Figure 2.9
Stress distribution in polymer matrix surrounding a rubbery impact
modifier particle (Stevenson, 1995)
In the case of additives where the modulus is higher than the polymer matrix,
the tensile stress is amplified at the poles rather than equator of the particle and much
reduced stress is found at the equator. Even though the stress distribution is different;
the stress concentrations are still able to induce shear yielding and crazing and are
therefore able to increase the impact resistance of the material.
While providing sites of stress concentration in the polymer matrix, rubbery
impact modifier is also able to elongate significantly without completely debonding
from the matrix or completely fracturing, which can help keep crazes from becoming
cracks. It means that impact modifier can restrain craze growth by bridging the crazes.
38
2.3
Impact Modification
The modification of PVC by the incorporation of impact modifier to improve
the toughness is a common industrial practice. The morphology and subsequently the
properties of the PVC itself are very sensitive to processing conditions. Benjamin
(1980) and Bystedt et al. (1988) have reported that the optimum ductility occurred
when some of the primary particles remained as a dispersed phase in the PVC
continuum. Thus, the effectiveness of impact modifiers to modify the toughness of
PVC not only depends on their degree of dispersion and distribution and good
adhesion to the PVC matrix but also on the presence of primary particles of PVC.
2.3.1 Theory of Impact Modification
Mertz et al. (1956) have proposed the earliest mechanism of impact
modification in which high impact polystyrene (HIPS) was used in their study. They
suggested that the increased energy absorption in the heterogeneous blend represented
the energy required to fracture the rubber particles as cracks passed through them.
This model is inadequate since the energy absorbed by composites far exceeded than
that required breaking the rubber particles (Newman and Strella, 1965).
Newman and Strella (1965) proposed that increased energy absorption in the
rubber-modified plastics was caused by the large energy involved in the local
deformation or cold drawing of glassy the matrix polymer. They associated this
increased cold drawing with an increase in free volume of the glassy matrix near the
rubber particles. Such was because the rubber particle, with Poisson ratio near 0.5
exhibited no volume change on deformation, then the lack of volume change in the
rubber must be due to an accentuated expansion of the matrix immediately
surrounding the rubber particle. This effectively lowered the glass transitions
39
temperature of the surrounding matrix, making it deforms more easily, and absorbed
more energy in the viscous flow process.
A craze theory developed by Bucknall and Smith (1965) proposed that the
rubber particles increased toughness by inducing greater crazing prior to fracture. The
increased degree of crazing was accompanied by greater energy absorption. Besides,
rubber particles lowered the craze initiation stress by providing sources of local stress
concentration entirely in the matrix and further strengthened the craze by bearing
(relevant) a portion of the triaxial stresses present at the particle-matrix interface
(equators). Thus, crazes initiated and terminated at rubber particles. It can be
concluded that the function of rubber particles was to promote and control
deformation in the matrix.
Bucknall’s crazing mechanism of impact reinforcement is the generally
accepted one until now because it has been demonstrated conclusively by using HIPS
system (Petrich, 1973). Currently, Lu et al. (2000) studied the toughening
mechanisms in commercial thermoplastic polyolefin blends and found that the crazes
started at the rubber-matrix interface, propagated through the matrix, and terminated
at the surrounding rubber particles. This indicates that the rubber phase acted not only
as a stress concentrator but also as a craze stabilizer to help prevent crazes from
transforming into premature cracks that could lead to catastrophic failure.
Lutz (1993) reported that the impact strength increased monotonically with
impact modifier particle size until an optimum was reached. For PS, large particles
were needed to yield by multiple crazing whereas in PVC, small particles were
needed to yield predominantly by shear band formation. Liang and Li (2000) divided
thermoplastic polymer matrices into two types, brittle matrix and ductile matrix. For
rubber-toughening brittle polymer system, such as PS and PMMA, the external
energy is mainly dissipated by the formation of crazing in the matrix. On the contrary,
for rubber toughening ductile polymer such as PVC (PVC is intrinsically more ductile
40
than other glassy plastics such PS) the dissipation of the external impact energy
depends on the shear yielding of the matrix.
2.3.2 Impact Modified PVC
PVC systems modified with EVA and CPE have shown that the EVA or CPE
with minimum impact modifier concentration envelops the PVC primary particles to
form a network structure (Robinovic, 1983). This structure was able to dissipate the
impact forces without cracking and resulted in high impact strength. However, at
higher processing temperature (180 oC) the network structure was destroyed, and the
decrease in impact strength observed was attributed to a phase inversion in which the
modifier became distributed as finer droplets within a continuous PVC phase (McGill
and Wittstock, 1987).
The mechanism of PVC system modified with acrylic was completely
different than that in EVA or CPE systems. Instead of a network structure, the acrylic
impact modifier formed a distinct dispersed phase (acrylic particle) and continuous
phase (PVC) in order to achieve high impact strength. The impact strength obtained
from this system was independent of the processing temperature. This was because
the morphology of dispersed rubber particles in the continuous PVC phase was
maintained at higher temperature (Robinovic, 1983). Meanwhile, CPE system was
dependent on processing temperature, shear and time. Around 150 oC, the network
structure has not developed and beyond 200 oC, melting of primary particles resulted
in the CPE converting into spherical globs dispersed in the PVC matrix resulting in
poor impact strength (Robinovic, 1983; Siegman and Hiltner, 1984).
Siegmann and Hiltner (1984) studied the impact modification PVC with CPE.
The PVC/CPE blends were roll milled at temperature of 178 oC for 5 min and then
41
moulded to the desired thickness in the preheated press at 193 oC. The morphology of
the two phases system changed with increasing CPE content from a dispersion of
discrete CPE particles to a continuous CPE network, which surrounded the primary
particles.
The discrete particles of CPE had very little effect compared to that
achieved by continuous network of impact modifier in improving the impact strength
of PVC. The network structure was destroyed when the blend milled for longer times
or above the fusion temperature of the primary particles.
McGill and Wittstock (1987) found that both systems, acrylic (KM330)-PVC
and EVA- or CPE – PVC required a minimum melt processing temperature of about
170-175 oC before high impact properties were attained. This temperature provided
high energy to cause disintegration of PVC grains and dispersion of primary particles.
It seems that at least partial fusion of primary particles was necessary for high impact
strength.
ABS terpolymers have been widely used as impact modifiers in rigid PVC,
because the polybutadiene rubber phase dispersed in the PVC matrix to form small
discrete domains, and the graft terpolymer provided interfacial bonding between the
phases to permit efficient stress transfer and thus increased the impact strength but
lowered the rigidity of PVC-U. Deanin and Chuang (1986) reported that ABS had
less softening effect and gave the best overall balance of properties than CPE. The
reasons behind this effect were SAN had high modulus and was quite miscible in the
PVC matrix and a polybutadiene formed separate domains and did not soften the PVC
matrix, whereas CPE was both soft and flexible, and also fairly miscible in PVC
matrix, thus softening it more aggressively.
42
2.4
Filled PVC Composites
PVC resin plays important role in plastic industry as a major component of
composites manufacturing. During the last few years, researchers have concentrated
their efforts to develop natural fibre-filled PVC composites (Wenguang and La
Mantia, 1996). Various types of natural fibres such as wood fibres, wood sawdust,
rich husk ash, have been extensively investigated and reviewed (Matuana et al., 1998;
Sivaneswaren, 2002; Sombatsompop et al., 2003). Other common fillers for filled
PVC composites include calcium carbonate, talc, kaolin, carbon black, mica (Wee,
2001; Saad et al., 1999). Characterised by high stiffness and strength, natural fibre as
fillers offer a number of advantages over the currently used reinforced inorganic
materials in terms of cost on a unit-volume basis, flexibility during processing and
stiffness (Matuana et al., 2001) Although natural fillers have received increased
attention but the inorganic fillers are still widely used in PVC composites. Hence, this
section briefly discusses the use of inorganic fillers in the PVC.
2.4.1 Composite: Definitions and Categories
The word ‘composite’ means ‘consisting of two or more distinct parts’. A
composite material is formed when two or more materials are combined so that the
properties of the composite are different from, and usually better than, those of the
individual constituents. Composites are made up of continuous and discontinuous
mediums. The continuous medium is called matrix and the discontinuous medium,
which is usually the harder and the stronger one, is called reinforcement. The
properties of a composite are dependent on the properties of the constituent materials,
and their distribution and interaction (fibre-matrix interface)(Mahmood Husein Datoo,
1992).
43
Composite materials can be broadly classified into three categories: particulate
composites, fibrous composites and laminated composites (Mahmood Husein Datoo,
1992). The definition of fibrous composites is referred to the fibre which has the
particle size longer than 100 µm with a length to diameter ratio lesser (aspect ratio)
than 10, whereas the opposed particle size as stated above is referred to the particulate
composites. (Katz and Brandmaier, 1987)
The main roles of the matrix are to bind and transmit and distribute stresses
among the individual fibres, and to prevent the fibres separation and to give them
desired orientation. The matrix also provides protection against both fibre abrasion
and fibre exposure to moisture or other environmental conditions, and causes the
fibres to act as a team in resisting failure and deformation under load. The maximum
service temperature of the composites is limited by the matrix ((Katz and Brandmaier,
1987; Miller, 1996)
Although thermoset polymers have some great virtues when used as matrices in
plastic composites such as low viscosity to facilitate thorough wetting of reinforcing
particles, economical for production large components and high softening points,
however recent years have seen rapid growth in the used of reinforced thermoplastic
polymers. The major advantage of thermoplastic matrix is that forming is possible by
injection moulding or extrusion techniques. These are the most economical processes
when cheap and precise manufacture of very large quantities of components is
required (McCrum et al., 1997). However, some special consideration must be made
for thermoplastics due to their poor high-temperature capability (Collyer and Clegg,
1986).
Most of the PVC is used as composite matrix in the mineral filler-filled PVC
composites. Calcium carbonate (CaCO3) has been extensively used in PVC
composites to enhance mechanical and thermal properties of PVC, such as hardness,
stiffness and heat resistance. However, the use of fillers at high loading leads to a
44
decrease in yield stress, tensile strength and ductility compared to the original
polymer (Saad et al., 1999). Recently, PVC matrix is used as the matrix for nano
CaCO3 particles. The impact strength, flexural modulus and softening point
temperature of PVC are significantly enhanced after addition of 0-15 phr nano CaCO3
but the yield strength and elongation at break of PVC are decreased (Chen et al.,
2004).
PMMA treated talc is an other inorganic filler used as filler in the PVC matrix.
The dispersion of talc and the mechanical properties of PVC composite especially the
impact strength are found to be improved. The enhancement of interfacial adhesion is
attributed to the impact strength improvement (Xie et al., 2001). Agalmatolite mineral
filler is also used in the PVC matrix. The composite made with agalmatolite shows
slightly higher values in Young’s modulus and elongation at break than those using
CaCO3. Thus the resistance to elastic deformation and plasticity is enhanced when
agalmatolite is used in PVC composites (Pedro et al., 2001)
The previous findings mentioned above show that PVC thermoplastic is also
competent to be a good matrix in the composite system.
Although unlike
thermosetting resins, if more ductile and versatile PVC thermoplastic is modified with
some consideration on heat processing, then the potential to use PVC as matrix in the
thermoplastic composite is possible.
2.4.2 Filler and Reinforcement
The basic purpose of fillers is to ‘fill’ a plastic that is to increase the bulk at
low cost and to improve the economics. With good adhesion between filler and
polymer, the filler can play a role in improving the mechanical properties of the
polymers (Murphy, 2001). Therefore, currently the primary purpose for using fillers
45
in thermoplastics is to modify properties such as stiffness, hardness, thermal stability
and shrinkage, instead of reducing the material cost. In this case, the fillers function as
the reinforcing fillers in the composites. Reinforcing fillers are additives, which
improve the tensile strength and tear resistance of the composites whereas extenders
reduce both of these properties. In general, the less fibrous (more particulate) fillers,
which have the lower aspect ratio, provide less reinforcement (Schwartz, 1987).
Whether extender or reinforcing filler, the effect of fillers on the composite
properties are largely dependent on the mean particle size, particle shape, particle size
distribution and the bond strength between filler particles and polymer matrix
(Wiebking, 1986). Most filler do not consist of particles, which are all the same size
and the same shape. The shape of the particles affects the modulus and other
mechanical properties significantly. Spherical particles are less likely to initiate
cracking compared to more slender particles. However, flat platelet-type particles tend
to produce stronger bond between the filler particle and matrix, due to increased
surface area available for bonding. One measurement of shape is the aspect ratio. The
greater aspect ratio, the greater the increase in bonding area available, which usually
improves mechanical properties. (Miller, 1996). Example of aspect ratio calculation is
illustrated in Figure 2.10.
According to Wiebking (1986), the flexural modulus or stiffness of PVC
composite was directly proportional to the aspect ratio of the filler being used. A high
aspect ratio can also increase the tensile properties of PVC composite by providing
more surfaces to contact the polymer. As a material is made stiffer, it also becomes
more brittle. Miller (1996) reported that the tensile strength depended on the
interfacial bond strength, which determined the distribution of stress between filler
and matrix. He concluded that, in general, the smaller the average size of the filler
particles, the greater their surface areas and the greater the bonding, resulting in
composite with good tensile strength.
46
Figure 2.10
Aspect ratio calculation (Wiebking, 1986)
2.4.2.1 Mineral Fillers
As mentioned earlier, mineral fillers have been widely used in the PVC
formulations. Among the mineral fillers used in the PVC are CaCO3, clay, talc, mica
and so forth. CaCO3 is the predominant filler used in PVC composites because of the
cost advantages and other appealing properties, which includes strong resistance to
thermal degradation during processing. Clays are useful for PVC in some specific
application such as electric insulator products. Meanwhile talc, mica, and other silica
are mainly employed with the aim of lowering material cost (Schlumpf, 1993).
Another category of filler materials used in PVC is termed “functional filler”
and this includes glass fibre, glass sphere, carbon fibres, aramid fibres, nano –clay and
nano calcium carbonates (Schlumpf, 1993; Wan et al., 2003; Chen et al., 2004) Their
use is mainly for consideration on the performance of the composites rather than of
cost. Although these organic fillers are low-cost on weight basis, their densities
(specific gravities about 2.5) can increase the cost on volume basis and make
processing more difficult.
47
2.4.2.2 Organic Fillers
Organic fillers such as wood flour, pulp fibre, rice husk are also used in PVC
compounds. They possess low specific gravities (about 1.4) and when used to extend
the resins they offer a significant cost saving. However, the use of cellulosic fillers in
the PVC materials is not as common as in polyolefins (polypropylene and
polyethylene).
Organic filler or natural fillers are biological structures composed mostly of
holocellulose (combination of cellulose and the hemicellulose) and lignin, and other
traces of plant materials, namely ash content and extractives (a group of cell wall
chemicals mainly consisting of fats, fatty acids, fatty alcohol and so forth). The
inorganic content can be quite high in plants containing large amounts of silica. The
extractives can be removed by one or several extraction procedures (Han and Rowell,
1997).
Natural fibres or fillers are rich in hydroxyl groups, which are responsible for
moisture sorption via hydrogen bonding, bio-degradation and thermal degradation of
the fibre whereas lignin is thermally stable but is responsible for the UV degradation.
Generally, without non-wood fibres, the fibres contain 60-80 % cellulose, 5-20 %
lignin and up to 20 % moisture. The hydrogen bonds and other linkages provide the
stiffness to the fibres (Saheb and Jog, 1999). Figure 2.11 shows the structure of
cellulose molecules. They have a tendency to form intra and intermolecular hydrogen
bonds.
Low thermal stability of natural fillers is the primary drawback. The thermal
degradation of natural fillers is a two-stage process, namely degradation of
hemicellulose and cellulose at low temperatures (220-280 oC) and degradation of
lignin at high temperatures (280-300 oC). The suggested processing temperatures are
thus limited to about 200 oC because of the possibility of natural fillers degradation
48
and/or the volatiles emissions that could affect the composites properties if processed
at higher temperatures. This factor will limit the type of the thermoplastics that can be
used with agro-fibres to only commodity thermoplastics.
O
H
OH
OH
H
H
H
C H 2O H
H
OH
OH
H
O
O
H
H
O
H
O
OH
H
H
H
H
H
OH
H
H
O
O
H
OH
H
H
OH
H
O
O
C H 2O H
C H 2O H
C H 2O H
n
n= repeat unit
Figure 2.11
Cellulose molecular structure (Han and Rowell, 1997)
Another primary drawback is the high moisture absorption of the natural
fillers. The moisture absorption can result in swelling of the fibres, dimensional
variation in composites and affects the mechanical properties of the composites. The
moisture evaporation, during processing of thermoplastics composites can lead to
poor processability and porous products. (Sanadi et al., 1997).
Uniform distribution and interaction of natural fillers is also important, so that
as many polymer chains as possible can be bound to the free filler surface. However,
natural fillers have poor interactions with the polymer matrix and tend to aggregate
among themselves due to strong hydrogen bonding, which holds the fillers together,
thus the fillers do not disperse well in a hydrophobic polymer matrix. Due to the poor
adhesion at the fibre-matrix interface, the fillers do not function as an effective
reinforcement system. Modification or surface treatment of the fibres with suitable
chemical reagents prior to processing can lead to good dispersion and adhesion,
significantly improves mechanical properties and also reduces water absorption of the
composites.
49
Thus, the important factors, which need to be considered in the application of
natural fibres as fillers or reinforcements in the composite system, are;
•
thermal stability of the fillers
•
surface adhesion characteristics of the fillers
•
dispersion of the fillers
The incorporation of wood fibre derived from cellulose into PVC matrix has
been studied extensively by Matuana et al. (1997, 1998, and 2001). The main reason
for using wood fibre or fibrous cellulose materials lies in the fact that these fibres
offer a number of advantageous over currently used reinforcing inorganic materials in
terms of cost on unit volume basis, flexibility during processing and stiffness.
Matuana et al. (2001) studied the photo-aging and stabilisation of rigid
PVC/wood-fibre composites. The experimental results showed that wood fibres were
effective sensitisers and that their incorporation into a rigid PVC matrix has
accelerated the photo-degradation of the PVC matrix when exposed to UV radiation.
They also reported that the light stability of these composites could be improved quite
efficiently with the addition of rutile titanium dioxide photoactive pigment during
formulation. In their previous investigation, the incorporation of wood fibre increased
stiffness and melt viscosity of the composites and limited the potential of producing a
foamed composite with high void fraction (greater than 20 %). However with good
treatment of fibre (silane), the foamed PVC composites with void fraction larger than
20 % were successfully achieved (Matuana et al.,1997).
Mengeloglu (2001) has studied the effects of impact modifiers such as
methacrylate-butadiene-styrene (MBS), all acrylic (ACR) and CPE on the properties
of rigid PVC/wood fibre composites. The wood fibre from hardwood maple was used.
Based on the mechanical property testing, the author concluded that the MBS and
ACR were more efficient and effective in improving the impact resistance of the
50
composites than the CPE modifier. Meanwhile, the tensile strength and modulus of
composites were significantly decreased by the addition of all of the impact modifiers.
The effect of rice husk ash (RHA) in the PVC-U has been studied by
Sivaneswaran (2002). The RHA-filled PVC has been impact modified with ABS and
the coupling agent with Lica 12. The results showed that the sample containing 8 phr
ABS and 40 phr RHA fillers treated with Lica 12 was the most effective formulation
in terms of flexural modulus, impact strength and cost.
Sombatsompop et al. (2003) have used sawdust as filler in the PVC to examine
the effect of sawdust content on structural and thermal changes, and rheological and
mechanical properties of PVC composite. The results revealed that the extrudate swell
monotonically decreased, up to 33.3 wt % sawdust content, and became independent
for sawdust content at greater than 33.3 wt %. Meanwhile, tensile, impact, flexural
and hardness properties considerably decreased with up to 16.7 wt % sawdust content
before levelling off at higher sawdust loading. The decrease in mechanical properties
was associated with the presence of moisture, interfacial defects and fibre dispersion
in PVC matrix. Thermal degradation of composite also decreased with increasing
sawdust content, which was caused by chlorine atoms cleavage due to strong
hydrogen bonds of wood fibre and PVC molecules. However the glass transition
temperature was found to increase after adding 16.7 wt % sawdust due to strong
hydrogen bonds and polar-polar interaction between PVC and sawdust molecules.
2.4.3 Filler-Matrix Interface
One of the factors controlling the performance of the composite materials is
the bond between the filler and the matrix. The localized stresses are usually highest
at or near the interface, which may be the point of premature failure of the composite.
51
As a result, a high interfacial strength is desirable to maximize the overall composite
strength. The filler-matrix interface bond acts as a bridge to allow the dispersed phase
(filler) to ‘communicate’ with matrix to transmit the stress or strain due to a
mechanical load from one phase to the other (Shackelford, 1996).
The interface must have appropriate chemical and physical features to provide
the necessary load transfer from the matrix to the filler. The use of a coupling agent
can provide improved interfacial condition (Katz and Brandmaier, 1986).
2.4.3.1 Coupling Agents and Surface Modification
The strength performance of the cellulosic fibre/polymer composites is
generally lower compared to unfilled polymer. The decreased strength is likely a
result of poor adhesion and/or dispersion of fibres due to the natural incompatibility
of phases during mixing of the hydrophilic cellulosic fibres with the hydrophobic
polymer matrix. To improve the adhesion between fibres and polymer, coupling
agents are usually used. Coupling agents are able to react chemically on both ends
during processing, with the fibres on the one side and the polymer on the other, thus
creating a chemical bridge at the interface (Xanthos,1983; Raj et al., 1990; Ahmad
Fuad et al., 1997; Rozman et al.,1998; Sivaneswaren, 2002).
The scheme for the reaction of silanes coupling agent (for instance) with
cellulosic materials is shown in Figure 2.12 (Ahmad Fuad et al., 1997). In the first
step, silanes are hydrolyzed to form alkoxysilanol groups with water molecules on the
surface of cellulosic fillers. In the second step, the absorbed alkoxysilanols condense
with the surface hydroxyl groups of cellulosic materials to form ether bonds. The
alkoxysilanols attached to hydroxyl groups of cellulose and/or lignin at the surface of
cellulosic materials were accomplished through the ether linkage (-O-) via structure 1,
as illustrated in Figure 2.12. This structure assumed the condensation of
alkoxysilanols to the filler surface (covalent deposition) has involved only one alkoxy
52
group of alkoxysilanols. However, silanols are also known to condensate amongst
themselves (intermolecular silane formation) during hydrolysis (structure II).
Step 1:
X − Si(OR ) 3 ⎯hydrolysis
⎯⎯
⎯→ X − Si(OH) 3
Step 2: Reaction with filler surface
+ OH
+
X Si
OH
OH
O
H
H
OH
X Si
O
Filler Surface
X Si
OH
OH
OH
H
OH
Filler Surface
X Si
OH
OH
OH
O
O
H
OH
Condensation
O
X Si
O
OH
Structure II
Figure 2.12
+
OH
X Si
OH
O
OH
X Si
O
Filler Surface
O
Filler Surface
OH
X Si
O
OH
Structure I
Bonding mechanism of silane coupling agent to filler’s surface
(Ahmad Fuad et al., 1997)
According to Xanthos (1983) and Raj et al. (1990) the wood flour or fibres has
the potential to be used as reinforcing fillers in the thermoplastics when they are
treated with chemical reagents. Therefore, various chemical reagents have been
53
employed to enhance the compatibility between the constituent materials. In order to
overcome the incompatibility between cellulosic fibre and PVC, Kokta et al. (1990)
have assessed the effects of various types of isocyanates such as poly(methylene
polyphenyl isocyanate)(PMPPIC), toulene,4-diisocyanate (TDIC), hexamethylene
diisocyanate (HMDIC) and ethyl isocyanate (EIC) as coupling agents.
The
mechanical
properties
of
hardwood
aspen
in
the
form
of
chemithermomechanical pulp (CTMP) and sawdust were studied (Maldas and Kokta,
1991). The results showed that the isocyanates acted either as a promoter or inhibitor,
depending on the concentration of the isocyanates used. For example, when used with
moderate concentration (0.5 to 5 % by weight), isocyanates promoted maximum
mechanical properties (tensile and flexural properties) whereas with greater
concentration, the mechanical properties deteriorated. PMPPIC had the best reactivity
among the four types of isocyanates studied and offered better performance of
composites. A stronger interface formed due to the delocalized electrons of benzene
ring in PMPPIC chemical structure provided little polarity, which interacted with the
opposite polarity of PVC developed by the presence of electronegative chlorine and
electropositive carbon and hydrogen. Besides that, the nature of pulp also played
important role in the mechanical properties of composites. The CTMP fibres
performed better in stress and modulus properties of composites than sawdust fibres.
It was explained by the dissimilar preparation techniques. CTMP fibres were
separated by chemical and mechanical means whereas sawdust fibres were separated
by cutting in mechanical way only. Therefore CTMP fibres possessed more specific
area leading to better polymer linkage at interface.
The effectiveness of other coupling agents has been studied. Matuana et al.
(1998) have studied the effects of various types of coupling agents such as
aminopropyltriethoxy-silane
(A-1100),
dichlorodiethylsilane
(DCS),
phthalic
anhydride (PA) and maleated polypropylene (E-43) on the compatibility between
wood veneer laminates and PVC. The effectiveness of surface treatment on the wood
–fibres in the PVC/wood fibre composites was investigated. The results showed that
the adhesion between PVC and wood veneer laminates was significantly improved
54
when wood veneers were treated with A-1100, while no improvement was observed
for the other coupling agents. The improvement was attributed to the fact that A-1100
treated wood veneer chemically reacted and formed an ionic bond with the matrix
because of the highly electronegative nature of chlorine atoms.
Recently, the rice husk ash (RHA) filled PVC-U matrix was investigated
(Azman Hassan and Kannan, 2001). RHA was modified with silane (Prosil 9234),
titanate (Lica 12 and Lica 38) and zirconate (NZ 44) coupling agents. The results
showed that the impact strength and flexural strength of impact-modified PVC
decreased with increasing RHA contents, however flexural modulus was increased.
The coupling agents used improved the mechanical properties but in overall
application, Lica 12 provided the optimum balance of properties for impact modified
PVC-U/RHA composites.
These recent studies revealed that although the strength property of
PVC/cellulosic fibre composites increased slightly after fibre treatments, the strength
property of the composites was still less than the base polymer, i.e., PVC. Therefore
PVC/cellulosic fibre composites with similar or greater strength to unfilled PVC have
not yet been reported in the literature. This is because an appropriate coupling agent
or its suitable form of application for PVC/cellulosic fibre composites has not yet
been identified.
2.5
Oil Palm Empty Fruit Bunch -Polymer Composites
As mentioned before most of the published papers have reported the use of
EFB fibre or filler as reinforcement in the thermoplastics polymers such as
polyethylene (Mohd Ishak et al., 1998), polypropylene (Rozman et al., 2001) and
polystyrene (Sarani et al., 2001) and in thermosets such as polyester (Hill and Abdul
55
Khalil, 2000 ; Abdul Khalil et al., 2001) and phenol-formaldehyde (Sreekala et al.,
1996; Sreekala and Thomas, 2003). However, areas for using of EFB fibres or fillers
in the PVC composites are still wide, especially in terms of the processability, thermal
stability-related to mechanical properties of the composites (Sombatsompop et al.,
2003).
2.5.1 Oil Palm Empty Fruit Bunch Fibre and its Chemical Composition
Oil palm empty fruit bunch (EFB), one of the by-products of oil palm milling
process, can be found in abundance in palm oil mills in Malaysia. Compared to other
by-products such as oil palm trunk (OPT) and oil palm fronds (OPF), the EFB has the
economical advantage of being collected at the oil palm mills. Currently, Sabutek
Sdn. Bhd, Ipoh, Perak, Malaysia has commercially produced the pulverized EFB
fibres and fillers.
The EFB fibres are derived from oil palm tree (Elais guineensis) component.
The chemical composition of untreated EFB fibre strands has been reported by Peng
(2002) as shown in Table 2.3.
Table 2.3: Chemical analysis of EFB (Peng, 2002)
Chemical Composition
Percentage (%)
Extractive
2.3
Holocellulose
82.5
α-cellulose
60.6
Lignin
17.2
Hemicellulose
32.5
Ash content
5.4
56
2.5.2 Utilization of EFB Fibre in Polymer Composites
Utilization of short EFB as a reinforcement in phenol-formaldehyde (PF)
resins has been studied by Sreekala et al. (1996). Four different fibre lengths of 20,
30, 40 and 50 mm with various fibre loadings were used for composite fabrication by
means of hand lay-up. The tensile, flexural and impact properties showed
improvement upon reinforcing with the fibre. The elongation, brittle nature and
buckling characteristics of PF resin were considerably improved by incorporating the
fibre. The fibre length of 40 mm and at 38 % fibre loading has produced the
maximum tensile and flexural strength. Fibre entanglement at higher fibre length was
the reason for the decrease in properties beyond 40 mm fibre length. Meanwhile the
impact properties showed linear enhancement with increase in fibre length up to 50
mm. However, for the best balance of mechanical properties, the optimum fibre
length and fibre loading were considered to be 40 mm and 30 %, respectively.
EFB fibre is also utilized in thermoplastic composites. Rozman et al. (1998)
have studied the effect of compounding techniques, the effect of oil palm EFB filler
loading and the effect of coupling agents on the mechanical properties of EFB/PP
composites. The study revealed that the incorporation of EFB into PP matrix resulted
in the improvement in the tensile modulus. However, the tensile strength, elongation
at break and impact strength decreased with increasing filler loading. Composites
produced by internal mixer have displayed higher mechanical properties than those
produced by extrusion. The better performance has been attributed to the effectiveness
of the internal mixer in improving the wetting of the filler surface. Meanwhile, the
incorporation of compatibilizer and coupling agent, that is, maleic anhydridemodified PP (Epolene E-43) and 3-Aminopropyl triethoxysilane (3-APE),
respectively, have produced composites with improved tensile and impact strength.
The presence of coupling agent and compatibilizer has also affected the amount of
water absorbed. The water absorption decreased as the amount of coupling agents
increased.
57
The effect of chemical modified oil palm EFB, fibre-matrix interaction of
composites, the effect of silane-based coupling agents treated EFB, and acrylic acid
based compatibilizers on the mechanical properties of high density polyethylene
(HDPE) also has been investigated by Mohd Ishak et al. (1998). They have found that
tensile modulus of EFB-HDPE without chemical treatment showed an increase,
whereas tensile strength, elongation at break and impact strength decreased with the
increasing filler loading. The strong tendency of EFB to exist in the form of fibre
bundles, poor filler-matrix interaction was believed to be responsible for the poor
strength displayed by the composites. Meanwhile, almost all chemical treatments
increased the stiffness of the composites but limited improvement has been observed
in the case of tensile strength. This has been attributed to the presence of fibre bundles
that remained intact even after several types of chemical treatment have been carried
out. Scanning electron microscopy (SEM) micrograph revealed that the main energyabsorbing mechanisms contributing towards toughness enhancement was through the
fibre bundle pullout process.
Rozman et al. (2001) in their recent paper reported the effect of oil extraction
of the oil palm EFB on the mechanical properties of PP/EFB/glass fibre hybrid
composites. The results showed that composites with oil-extracted EFB produced
significantly higher flexural and tensile strength and toughness than those without
extraction. The study showed that the efficiency of coupling agent was enhanced with
the removal of oil from the EFB surface. The main reason being the oil extraction has
resulted in the formation of continuous interfacial region i.e. good adhesion between
EFB and PP matrix.
Abdul Khalil et al. (2001) have used other methods to improve the
compatibility between oil palm EFB and the polyester polymer matrix, where EFB
was chemically modified using non-catalysed reaction with acetic, propionic and
succinic anhydrides. The effects of various anhydride modifications on mechanical
properties and water absorption of oil palm reinforced polyester composites were
investigated. The properties were improved for modified fibres whereas unmodified
EFB fibres exhibited poor mechanical properties and higher water absorption. It was
58
concluded that the chemical modification resulted in hydrophobic fibre and hence
improved the fibre-matrix bonding.
Another research, oil palm EFB was used in the polystyrene matrix as reported
by Sarani Zakaria et al. (2001). The benzylation process treatment was used in order
to decrease the hydrophilic property of EFB fibres where the hydroxyl groups were
replaced by aromatic rings from benzyl groups to produce benzylated EFB fibres. The
results showed that the modified EFB/polystyrene produced better mechanical and
physical properties than unmodified EFB/polystyrene composites, due to the
enhancement of compatibility between EFB fibres and polystyrene.
Recently, Sreekala and Thomas (2003) studied the effect of fibre surface
modification on water-sorption characteristics of EFB fibres. Surface modification
such as mercerization, latex coating, gamma irradiation, silane treatment, isocyanate
treatment, acetylation and peroxide treatment were used to reduce the hydrophilicity
of fibres. Treatment reduced overall water uptake at all temperatures (30, 50, 70 and
90 oC). Such reduction was due to the physical and chemical changes in the fibre upon
modifications. The effect of sorption on the mechanical performance of the treated
and untreated fibres was also investigated and it was found that the properties of the
fibres decrease upon sorption and regains on desorption.
Based on the literatures reviews, the following conclusions are derived. The
addition of EFB fibres or other natural fillers as reinforcement generally has increased
the modulus of the composites while decreased the strength, elongation and water
absorption. An alternative way to improve the composite properties is by modifying
the fibre surface by chemical reagents. However, some of the treated fillers have not
shown any improvement and they even destroyed the composites because they could
not react with a hydroxyl groups. Rowell (1997) has suggested that the basic
principles that must be considered in selecting a reagent and a reaction system are as
follows: (1) the chemical must contain functional groups to react with the hydroxyl
groups on the fibres, (2) the moisture content must be reduced, due to OH group in
59
water being more reactive (rate of hydrolysis) than the OH group available in the
fibre. The favourable condition is a reaction, which requires a trace of moisture
content and (3) the chemical bond formed between the reagent and the fibres
components. In the order of stability, the types of covalent chemical bonds that may
be formed are ethers, acetyls and esters. The covalent carbon-oxygen bond i.e. the
ether bond is the most desirable.
2.6
Theory of Mechanical Properties of Filled Composites
Both the matrix and fibre properties are important in improving mechanical
properties of the composites. Modulus is a bulk property, which depends primarily on
the filler properties such as geometry (aspect ratio), particle size distribution and
concentration of the filler, whereas tensile strength of a composite depends strongly
on local polymer-filler interaction as well as the above factors. The filler particle
geometry has significant influence on the strength of a filled polymer. Impact strength
of the composite depends on the degree of fibre-matrix adhesion and is very complex.
The microscale morphological changes in the matrix caused by the fibre affect the
impact strength of composites.
The development of the most of the theories is generally based on the
assumption that perfect adhesion takes place between matrix and dispersed phases. By
perfect adhesion, means that the displacement continuity is maintained at the
boundary of the two phases when stress is applied to the system. In many practical
cases, however, it cannot be assumed that there is perfect adhesion between matrix
and dispersed phases, and in extreme cases, there is no adhesion at the boundary. In
this case, the modulus equation is considerably different from the one for perfect
adhesion (Kunori and Geil, 1980).
60
One of the first equations developed was that of Einstein’s. It is valid only for
composites filled with low concentrations of non-interactive spheres and assumes that
the filler is very much more rigid than the matrix (Kunori and Geil, 1980; Maiti and
Subbarao, 1991; Zaini et al., 1994). For cases when there is perfect adhesion between
phases, the result is:
(
E
c = 1 + 2.5φ
f
E
p
)
(2.1)
and for the case when there is no adhesion between the two phases :
E
E
(
c = 1+ φ
f
p
)
(2.2)
where Ec, Ep and φf are the modulus of composite, modulus of polymer matrix and
volume fraction of filler, respectively. To account for interparticle interactions at
higher filler concentrations, the following equation from Guth-Smallwood is more
relevant (Zaini et al., 1994). This equation is an extension of Einstein’s theory and is
valid for the perfect adhesion system.
E
c = ⎛⎜1 + 2.5φ + 14.1φ 2 ⎞⎟
f
f⎠
⎝
E
p
(2.3)
Kerner (1969) afterward derived a versatile equation to describe the
reinforcing action of the spherical fillers by assuming perfect bonding of the spherical
grains to each other:
⎡
⎤
⎡
⎤
φ G / ⎢⎛⎜ 7 − 5ν ⎞⎟G + ⎛⎜ 8 − 10ν ⎞⎟G ⎥ + φ / ⎢15⎛⎜1 − ν ⎞⎟⎥
f
f
p
p
p
f
p
p
⎠
⎝
⎠
⎝
⎠
⎝
⎣
⎦
⎣
⎦
c =
E
⎡⎛
⎤
⎡
⎤
p φ G / ⎢⎜ 7 − 5ν ⎞⎟G + ⎛⎜ 8 − 10ν ⎞⎟G ⎥ + φ / ⎢15⎛⎜1 − ν ⎞⎟⎥
p f ⎣⎝
p⎠ p ⎝
p⎠ f ⎦
p ⎣ ⎝
p ⎠⎦
E
(2.4)
61
where φf and φp are the volume fractions of filler and polymer respectively; Gf and
Gp are the shear moduli of filler and polymer, respectively. Since many types of filler
are much more rigid than the matrices, thus Equation (2.4) may be simplified to:
Ec
Ep
= 1+
15(1− ν p ) ⎛ φ
⎜ f
8 − ν p ⎜ 1 − φf
⎝
⎞
⎟
⎟
⎠
(2.5)
The most frequently used model is the Lewis-Nielsen model (also known as
modified Kerner’s model)(Nielsen, 1974). Lewis and Nielsen have put forward an
equation which is more applicable for fillers with lower aspect ratio. This equation is
for the system having perfect adhesion at the boundary. By modifying Equation (2.4),
they came to the following equation:
(
(
1 + ABφ
c =
f
E
1 − Bψφ
p
f
E
)
)
(2.6)
where
⎛ 7 − 5ν ⎞
⎜
p ⎟⎠
⎝
;
A=
⎛ 8 − 10ν ⎞
⎜
p ⎟⎠
⎝
⎡⎛ G ⎞ ⎤
⎢⎜ f ⎟ − 1⎥
⎢⎜⎜ G ⎟⎟ ⎥
⎢⎝ p ⎠ ⎦⎥
B= ⎣
;
⎤
⎡⎛ G ⎞
⎢⎜ f ⎟ + A ⎥
⎥
⎢⎜⎜ G ⎟⎟
⎦⎥
⎣⎢⎝ p ⎠
(
⎡ 1− φ
m
ψ = 1− ⎢
⎢
2
φ
m
⎣⎢
)⎤⎥φ
⎥ f
⎦⎥
A is a constant related to the Einstein coefficient and is a function of the filler’s
geometry, B is related to the relative shear moduli of filler, Gf and polymer, Gp, and
ψ is a reduced concentration term dependent on the maximum packing fraction, φm of
the filler in the polymer while υp is Poisson’s ratio of the polymer.
62
Maiti and Subbarao (1991) found that the data for both untreated and treated
wood flour-filled polypropylene composites fit Equation 2.1, while Equations 2.2 and
2.6 exhibited higher values of modulus. The higher values obtained from Equations
2.2 and 2.6 were due to the surface treatment of wood flour with the coupling agent
(Lica 38), which improved the interaction only marginally. The increase in modulus
was due to the restriction in the mobility of the polymer molecules in the presence of
wood flour. However, the increase was not very high because of the absence of
chemical interaction between wood flour and polypropylene.
In order to describe the dependence of mechanical properties (i.e., tensile
strength and tensile yield) of filled composites on the volume fraction of filler, the
equation from Nielsen (1966) and Nicolais and Narkis (1971), which expressed by
two-thirds power law relationship are given by Equation (2.7) and (2.8), respectively,
are commonly used:
σ
σ
σ
σ
c = ⎛⎜1 − φ 2 / 3 ⎞⎟S
f ⎠
⎝
p
(2.7)
c = ⎛⎜1 − Kφ 2 / 3 ⎞⎟
f ⎠
⎝
p
(2.8)
where σ c and σ p denote the given mechanical properties of the composite and the
matrix, respectively. According to Nielsen’s definition, parameter S in Equation 2.7
describes the stress concentration at the filler-polymer interphase arising from the
discontinuity in stress transfer. The maximum value of S is unity for “no stress
concentration effect,” which is valid for unfilled polymer. The lower the value of S
the greater the stress concentration effect (or poorer the adhesion), which is valid for
filled polymer composites. The weightage factor K in Equation 2.8 accounts for the
adhesion quality between the matrix and the inclusion or the filler. The lower K value
indicates better adhesion. The extreme case with K= 0 represents unfilled polymer.
63
For spherical inclusions in the extreme case of poor adhesion, K assumes a value of
1.21.
Nielsen (1966) has also proposed a simple model to predict the relative
elongation at break with perfect adhesion:
εc
εp
= 1 − φ f 1/3
(2.9)
where εp and εc are the elongation at break of the polymer and the elongation of the
composites, respectively. Maiti and Subbarao (1991) and Maiti and Lopez (1992)
found that the prediction values of relative elongation of untreated wood flour-filled
polypropylene composites and kaolin-filled polypropylene composites were slightly
higher than the experimental results. It was apparent that the presence of kaolin
particles or wood flour interferes with the stress transfer process, in particular in the
absence of any specific adhesion between polypropylene and fillers.
2.7
Recent Studies on Impact Modified PVC-U by UTM Researchers
Impact modified PVC-U is an area which is being actively pursued by the
researchers from Universiti Teknologi Malaysia (UTM). Azman Hassan (1996) in his
study on the effect of acrylic impact modifier particle size on unfilled PVC-U has
found that the effectiveness in decreasing the yield stress of unfilled PVC-U became
more pronounced with decreasing particle size. The smaller particle size impact
modifiers were also shown to be more effective in enhancing the impact strength of
PVC-U.
64
Wee, (2001) studied the effect of calcium carbonate fillers on the mechanical
properties of modified PVC-U. The different sizes and types of calcium carbonate
fillers were used to determine the most optimum formulation in terms of mechanical
properties of modified PVC-U and cost. He concluded that the impact-modified PVCU filled with 20 phr of 0.8 µm precipitated calcium carbonate was the most optimum
formulation based on the criteria.
Besides the use of mineral fillers, the application of RHA, which is an organic
material as a filler in impact modified PVC-U composites has also been studied
(Sivaneswaran, 2002). The sample containing 8 phr ABS and 40 phr RHA filler
treated with Lica 12 was found to be the most effective formulation in terms of
flexural modulus, impact strength and cost. This study showed that the strategy to
develop materials which possessed a significant improvement in toughness without
sacrificing the desirable stiffness properties at a moderate cost was achieved.
CHAPTER 3
MECHANICAL PROPERTIES OF COMPRESSION MOULDED PVC-U
COMPOSITES
3.1
Introduction
Unmodified poly (vinyl chloride) (PVC-U) is intrinsically more ductile than
other thermoplastics such as polystyrene, and when compared with polyethylene and
polypropylene, it is more rigid and stronger. However, it is extremely sensitive to
stress rate, temperature, and notching. Increasing the impact rate, reducing the test
temperature or providing notch as a stress concentrator, can dramatically reduce
PVC’s ductility (Grohman, 1994). PVC has to be modified in order to satisfy end-use
requirements for rigid applications. Thus, therefore impact modifiers are incorporated
to PVC to improve its ductility. The enhancement of impact properties of PVC by
introduction of a rubbery phase is a well-known phenomenon, which has been widely
exploited commercially. Basically, the effect of impact modifier is to shift the ductilebrittle transition of the PVC to the higher impact rate, lower temperature, or sharper
notch.
While PVC’s ductility is improved, there are other effects, which must be
considered such as the tensile and flexural properties of rigid PVC. Lutz (1993)
66
reported that these properties of PVC have adversely affected with increasing impact
modifier concentration.
The incorporation of soft rubbery impact modifier has
lowered the rigidity of the rigid PVC.
Modifiers with lower glass transition
temperature and greater compatibility have a greater effect on the impact strength.
Among the families of plastic tougheners, acrylic core-shell impact modifier (acrylic)
and chlorinated polyethylene (CPE) are commonly used in formulation of PVC,
particularly for window profiles or outdoor applications.
Rigid PVC is used in many applications where cost is a major factor. In order
to reduce the cost of products, as a result, fillers are often added in the rigid PVC
formulations. However, the incorporation of fillers into thermoplastics results in
stiffness enhancement but reduces the impact strength or toughness. Thus, the rubbery
impact modifier is added in the rigid PVC in order to produce a significant
improvement in toughness but at the expense of stiffness and strength. One of the
most important aspects in the modification properties of thermoplastics by using
fillers is to achieve a good combination of properties and processability at a moderate
cost. As far as mechanical properties are concerned, the main target is to strike a
balance of stiffness, strength, and toughness (Mohd Ishak et al., 2000)
The several advantages offered by natural organic fillers have gradually
stimulated the researchers to use these kinds of filler for plastics modification (Raj et
al., 1990). For instance, the application of EFB fibre as filler or reinforcement for
production of polymer filled composites has been reported by several researchers
(Zaini et al., 1996; Rozman et al., 1998; Abdul Khalil et al., 2001). The incorporation
of EFB into PP matrix has resulted in the improvement in tensile modulus, but the
tensile strength, elongation at break, and impact strength decreased with increasing
filler content. However, the application of compatibiliser and coupling agent has
improved the tensile properties and impact strength of the composites (Rozman et al.,
1998). The modification of EFB with anhydrides has improved the impact and
flexural properties of polyester reinforced with EFB (Abdul Khalil et al., 2001). In
terms of filler length, oil palm wood flour for all filler lengths has decreased the
67
mechanical properties of PP/Oil Palm wood flour composites with increasing filler
contents (Zaini et al., 1996).
Although EFB has been useful as a filler in the various polymers, the use of
EFB in PVC has not been studied extensively. Most of the researchers using PVC
have used wood flour, wood sawdust, and rice husk ash (Mautana et al., 2001;
Sivaneswaran, 2002; Sombatsompop et al., 2003). Therefore, the objectives of this
chapter are to discuss the impact and flexural properties of the PVC-U composites.
3.2
Experimental
This section describes in detail the materials, filler preparations, samples
preparation, density determination, impact and flexural testing, accelerated
weathering testing and water absorption property.
3.2.1 Materials
The suspension PVC resin used in this study, with solution viscosity K-value,
and trade name MH-66 was supplied by Industrial Resin Malaysia (IRM) Sdn.Bhd.
Tampoi, Johor, Malaysia. This homopolymer PVC is a medium molecular weight
resin designed for general purpose, rigid and flexible applications. Its specifications
are summarized in Table 3.1.
68
Table 3.1: Specifications of PVC suspension resin MH-66
Appearance
White Powder
Degree of polymerisation
1000 + 50
K-value
66
Specific gravity
1.4
Bulk density (g/cm3)
0.50+0.05
Volatile Matter (max) (%)
0.5
Foreign Matter (grain/100g)
15
Particle size (retained on 250 µ), (max) (%)
0.3
Table 3.2: Types of additives
Additives
Types
Manufacturers
Internal lubricant
Calcium Stearate (CaSt)
External lubricant
Stearic Acid (HSt)
Processing aid
(PA-Acrylic)
Pigment
Titanium Dioxide (TiO2)
Heat Stabilizer
Tin (Sn)
Elf Atochem
Impact Modifier
Acrylic
Elf Atochem
Chlorinated Polyethylene (CPE)
Filler
Oil Palm Empty Fruit Bunch (EFB)
Sun Ace Koh
Palm star
Kaneka (M) Sdn. Bhd.
Kromos
Dupont Dow Elastomers
Sabutek Sdn. Bhd.
The additives used in the PVC formulations are shown in Table 3.2. IRM Sdn.
Bhd also supplied most of the additives used in the formulations except for the impact
modifiers and filler. Kureha Chemicals supplied core and shell impact modifier with
a trade name of Paraloid KM355P. It consists of poly (methyl methacrylate) (PMMA)
as a shell while poly (butyl acrylate) (PBA) acts as a core. The chlorinated
polyethylene (CPE) for thermoplastic applications with trade name Tyrin 702P and
containing 36 % chlorine content was supplied by Dupont Dow Elastomers. The EFB
in the powder form was purchased from Sabutek Sdn. Bhd., Teluk Intan Perak. The
69
properties of EFB are shown in Table 2.3 (Chapter 2). The coupling agents used were
Prosil 9234 and NZ 44 supplied by Kenrich Petrochemicals, Inc. The Prosil 9234 is
silane-based with chemical name is n-octyltriethoxysilane, while NZ 44 is zirconatebased with chemical name is tris (2-ethylene-diamino) ethanolate. The chemical
structures of Prosil 9234 and NZ 44 are shown in Figure 3.1.
OC2H5
CH3CH2CH2CH2CH2CH2CH2CH2
Si
OC2H5
OC2H5
(a) n-octyltriethoxysilane
OC2H4-NH-C2H4-NH2
RO-Zr
OC2H4-NH-C2H4-NH2
OC2H4-NH-C2H4-NH2
(b) tris(2-ethylene-diamino)ethanolate
Figure 3.1
Chemical structure of (a) Prosil 9234 (b) NZ 44
3.2.2 Filler Preparations
The EFB fillers were supplied in bulk with unknown sizes by the supplier.
Thus, in this study a Restsch shaker AS200 was used to separate the EFB fillers into
different sizes. The shaking time was set at 10 minutes. The filler size used in this
study was less than 75 µm with filler distribution and filler morphology is shown in
Figures 3.2 and 3.3, respectively. EFB filler distribution was determined by using
70
Malvern Instruments Mastersizer. EFB fillers were dried in an oven at 105 oC for
about 24 hours to constant weight, the weight loss then being calculated. The original
moisture content of the EFB filler was found to be around 5 %.
Figure 3.2
EFB fillers distribution
Figure 3.3
Morphology of EFB fillers (Magnification of 600x)
71
The temperature and time duration used for drying process in this study were
referred from previous researchers who used natural fibre in their studies (Zaini et al.,
1996; Hill and Abdul Khalil, 2000). The dried EFB fillers were placed in desiccators
for cooling and were left in desiccators before dry blending with PVC and other
additives to produce the dry blends of PVC-U compounds.
Nano-precipitated calcium carbonate (NPCC) with filler size of less than 40
nm and extracted EFB filler size of less than 75 µm were also used as filler for the
composites. NPCC filler was supplied by NanoMaterials Technology, Singapore.
Extracted EFB fillers were also dried in an oven at similar conditions as unextracted
EFB fillers before dry blending. The preparation of extracted EFB fillers was reported
in detail in Chapter 5 (Section 5.2.2). The effect of NPCC and extracted EFB fillers
on the mechanical properties of the composites was investigated to compare with
unextracted EFB. This is a minor part of this study.
3.2.3 Coupling Agent Treatment of Filler
Filler treatment techniques and dosages of the coupling agent were applied as
advised by the manufacturers of the respective coupling agents. For zirconate
coupling agent (NZ 44), the PVC resin itself was treated rather than the filler. This is
contrary to silane coupling agent (Prosil 9234) where the EFB filler itself underwent
coupling agent treatment prior to dry blending process.
The dosage used for the Prosil 9234 coupling agent was 0.5 % by weight of
the filler. The Prosil 9234 was diluted in ethanol to make up 10 % solution for better
dispersion. The EFB filler was charged into a bench top tumbler mixer and coupling
agent was added slowly over the period of 15 minutes to ensure uniform distribution
72
of the coupling agent. The filler was continuously mixed for another 30 minutes. The
Prosil 9234-treated fillers were dried at 100 oC for about 2 hours.
The dosage of the NZ 44 coupling agent is a slight different. The manufacturer
recommended the dosage should be either 0.2 % or 0.5 % by weight of filler. This
dosage has also been used by the previous researchers and they found that this dosage
was able to improve the mechanical properties of filled composites (Ahmad Fuad et
al., 1997 ; Sivaneswaran, 2002). Since with increasing filler content, the PVC fraction
decreases correspondingly, the applied dosage of NZ 44 has to be adjusted. Thus, at
lower filler contents (at which level, the PVC predominates), 0.2 % by weight of PVC
was used. At higher filler contents (30 and 40 phr filler content), 0.5 % by weight of
EFB was applied. The coupling agent was diluted in propanol to assist distribution of
the coupling agent in the PVC resin prior to dry blending process.
3.2.4 Blend Formulations
The PVC-U dry blend formulations are shown in Tables 3.3a-3.3i, which were
based upon typical commercial PVC window formulations with some modifications.
The basis of this formulation was also used by previous researchers (Wee, 2001;
Sivaneswaran, 2002). The additives content were unchanged in the formulations
except for EFB filler, CPE, and acrylic impact modifiers. Based on the preliminary
study, the two-roll milled composite sheet became brittle as the filler content
incorporated up to 50 phr. Therefore, in this study the EFB filler content was only
varied from 10 to 40 phr.
73
74
75
76
77
78
79
80
81
82
3.2.5 Dry Blending
The purpose of dry blending is to obtain good homogeneity of the blends.
Before dry blending took place, the exact proportion of the resin and the additives
were weighed and mixed appropriately. PVC dry blending with additives was done
using a heavy-duty laboratory mixer. Each of PVC-U formulation as shown in Tables
3.3a-3.3i, except for formulations S45, S46, S48, was mixed at low speed mixing for 10
minutes before being collected. Low speed mixing was used to minimize the less
dense of additives from floating in the air and sticking on the wall inside the column
mixer. As a result, the percentage of homogeneity of dry blends was able to be
increased. The PVC-U dry blends were poured into the sealed plastic bags and stored
in the desiccators before used for two-roll milling process. The similar dry blending
process was applied to the PVC-U dry blends filled with coupling agent-treated EFB,
oil-extracted EFB and NPCC-200 fillers.
3.2.6 Two-Roll Milling
The dry blended PVC-U were milled and sheeted using a two-roll mill as
shown in Figure 3.4 with 10 minutes of milling time. The temperature used for the
front and back roller was 165 oC. The milled sheet as shown in Figure 3.5 was then
compression moulded.
83
Back Roller
Dry Blended
PVC-U
Front Roller
Figure 3.4
Figure: 3.5
Two roll milling of PVC-U dry blend at 165 oC
Two-roll milled composite sheet
84
3.2.7 Compression Moulding
A mould was designed and fabricated for compression moulding as shown in
Figure 3.6. The mould was designed to have five cavities and the size of each sample
was according to ASTM D256 (A) with thickness 3 mm. The two roll milled sheets
were placed into a mould with five cavities at 180 oC and 120 kg/m2, 3 minutes for
preheating, 5 minutes for compression moulding and 5 minutes for cooling before
being removed. The water circulation was used for the cooling process. All the
moulded specimens were then conditioned for 48 hours at 23 oC prior to testing.
Top Hot Platen
Mould Cavities
Bottom Hot Platen
Figure 3.6
compression
A mould with five cavities placed in between the hot platens before
85
3.2.8 Density Determinations
The density of EFB fillers was determined according to ISO 8962 using a
glass pyknometer with some modification as reported by Ahmad Fuad et al. (1993).
According to them, the standard describes only a method for determining the density
of polymer dispersion and not the density of solid powder-like particles.
The volume of the pyknometer was initially determined from the following
equations;
volume =
Vp =
mass
density
(M 2 − M1 )
ρw
(3.1)
(3.2)
where M1 is the mass of cleaned and dried pyknometer, M2 is the mass of pyknometer
filled with distilled water, in which both of them were weighed accurately to four
decimal places on a Mettler Toledo Analytical Balance Model AX 201. Vp is the
volume of the pyknometer and ρw is the density of water at the test temperature.
Since the test was carried out at a constant laboratory temperature of 24 oC, the
density of water was taken to be 0.9973 g/cm3.
The pyknometer was dried thoroughly again and approximately 2 g of the
dried EFB filler was placed into the bottle. The bottle was reweighed. It was then
filled with distilled water, stoppered, and shaken slightly to disperse the particles.
Care was taken to ensure absence of air bubbles. Excess water outside the bottle was
wiped clean with absorbent paper. The volume of distilled water, Vw was determined
as follows;
Vw =
(M 4 − M 3 )
ρw
(3.3)
86
where, M3 is
the mass of pyknometer containing the EFB, M4 is the mass of
pyknometer containing the EFB with distilled water.
Knowing the Vp and Vw, the volume of EFB filler, Vr was calculated as;
Vr = VP − VW
(3.4)
Thus, the density of the EFB, ρf would be:
ρf =
(M 3 − M 1 )
Vr
= ρw
(M 3 − M 1 )
(M 3 − M 1 + M 2 − M 4 )
(3.5)
(3.6)
The experimental density of the PVC-U and composites was determined
according to ASTM D792, Method A using a Mettler Toledo Model AX201 density
balance. The theoretical density of PVC-U and composite, ρ c was calculated using the
following equation;
ρc =
1
⎛ Wf ⎞ ⎛ WPVC ⎞ ⎛ Wadditives⎞
⎟⎟
⎟⎟ + ⎜⎜
⎜⎜ ⎟⎟ + ⎜⎜
⎝ ρf ⎠ ⎝ ρPVC ⎠ ⎝ ρadditives ⎠
(3.7)
where, Wf ,WPVC and Wadditives are weight fractions of filler, PVC resin and additives
in composite, respectively. ρ f , ρ m and ρ additivess refer to the density of filler, PVC resin
and additives, respectively.
87
3.2.9 Impact Testing
Specimens test bars for impact testing were moulded from the compressed
sheet according to the size specified in ASTM D256 (A). The specimens were
notched with a Davenport notch cutting apparatus. The notch depth was fixed at 2.6 +
0.02 mm with angle 45o.The Izod impact strength test was carried out on the notched
specimens using the IMPats pendulum impact tester at impact velocity of 3.0 m/s and
90o swing angle using a 7.5 J hammer at room temperature. The Izod impact strength
was calculated by dividing the indicator reading of impact energy by the cross
sectional area of the specimen. All the reported values for the impact testing were the
average of seven specimens.
3.2.10 Flexural Testing
Specimen test bars for flexural testing were also moulded from the
compressed sheet. The flexural test was conducted on the Instron Machine Model
5567 (static load cell of 30 kN) according to ASTM D790. The specimens, with
dimensions 125 x 13x 3 mm3, were tested at crosshead speed of 3 mm/min at room
temperature. The support span for the test was 51 mm. All the reported values for the
flexural testing were the average of seven specimens
The slope of the initial linear portion of the stress-strain curve represented
flexural modulus. Flexural modulus was represented the resistance to elastic
deformation under applied stress. The resistance to plastic deformation and failure
under applied stress was represented by flexural strength. They were calculated
according to the following equations;
88
Flexural modulus =
L3 ∆ W
4bd 3 ∆ S
(3.8)
Flexural strength =
3WL
2 bd 2
(3.9)
where W is the ultimate failure load (N), L is the span between the centres of support,
b is the mean width of the specimens (m), d is the mean thickness of the specimens of
the sample, ∆ W is the increment in load (N) and ∆ S is the increment in deflection.
3.2.11 Accelerated Weathering Testing
The specimen test bars were tested using ATLAS UV accelerated weathering
tester according to ASTM G53. The tester simulated the deterioration caused by
sunlight and rain by means of ultraviolet light and condensation. The ATLAS UV
accelerated weathering test apparatus consists of a corrosion resistant material test
chamber enclosing eight fluorescent UV lamps, a heated water pan, test specimen
racks and means for controlling and indicating operating times and temperatures.
The specimens were mounted in the specimen racks with the test surfaces
facing the lamps. The specimens were alternatively exposed to ultraviolet only (4
hours at 70 oC) and to condensation only (4 hours at 50 oC) in repetitive cycle without
interruption, 24 hours a day. Condensation was produced by exposing the test surface
to a heated, saturated mixture of air and water, while the reverse side of the test
specimen was exposed to the cooling effect of ambient air. The total exposure time
was 504 hours (3 weeks). The experimental was stopped at this total exposure time as
the PVC-U specimens (as an indicator) suffered a change in colour (from white to
89
yellowish). The durability of each specimen was evaluated by comparing the
mechanical properties of unweathered and weathered specimens.
3.2.12 Water Absorption Testing
The specimen test bars were immersed into the distillate water for 60 days at
room temperature according to ASTM D570. Water absorption was determined by
weighing the sample before and after immersion at specific time intervals. The water
absorption at any time, Mt was calculated from the following equation;
Mt =
Ww − Wd
Wd
(3.10)
where Wd and Ww are the initial dry weight and the weight after immersion in water,
respectively. The purpose of this test was to observe the influence of EFB filler and
impact modifiers content on the degree of water absorption of the specimens.
3.2.13 Scanning Electron Microscopy Study
Studies of the specimen impact-fractured surfaces were performed with a
JEOL model JSM-6301F scanning electron microscope (SEM). A small portion of the
fractured surface of impact-tested specimen was mounted on the copper stub and
sputter-coated with a thin layer of gold to avoid electrostatic charging during
examination.
90
3.2.14 Fourier Transform Infra-Red Analysis
Fourier Transform Infra-Red (FTIR) was used to identify the related
functional groups present in specimens. A small quantity of specimen was thoroughly
mixed with dry potassium bromide powder (KBr) in a mortar and then pressed at
pressure of 6 bars for 2 minutes to form a moisture-free KBr thin disc. The thin disc
was placed in a sample cup of a diffuse reflectance accessory and was then scanned
from 4000 cm-1- 370 cm-1 for 16 times to reduce the noise to signal ratio. All the
spectra of specimens were obtained from the KBr technique, using a Perkin Elmer
2000 Infrared Spectrometer.
3.3
Results and Discussion
This section discusses the density, impact strength, flexural properties,
accelerated weathering properties and water absorption of the composites. The
functional groups and impact-fractured surface morphologies of the composites
obtained from FTIR and SEM, respectively, will also be discussed.
3.3.1 Density of the Filler and EFB-Filled PVC-U Composites
The density of the EFB filler and PVC-U (So) found were 1.444 + 0.041 g/cm3
and 1.411 + 0.001 g/cm3, respectively. These values were within the known range of
densities reported by other researchers (Titow, 1991; Sreekala and Thomas, 2003).
The results showed that the density of EFB filler was slightly higher than that of
PVC-U matrix. Consequently, the density of the EFB-filled PVC-U composites
91
increased as the filler content increased from 0 to 40 phr, as shown in Figure 3.7. All
experimental densities obtained were lower than the theoretical densities calculated
using Equation 3.7.
The lowering of experimental densities was attributed to the presence of voids
within the filled composites. The voids probably occurred in the matrix, at the fillermatrix interface, or within the filler bundles. The presence of voids in natural fibrefilled polymer composites has also been noted by other researchers who found that the
void content increased as the fibre content increased (Hill et al., 2000; Klaric et al.,
2000). The SEM micrograph in Figure 3.8 shows the presence of voids at the fibrematrix interface in the composites. The hydrophilic nature of the EFB fillers might
have caused them to pick up moisture, which evaporated from the filler-matrix
interface during processing. This resulted in the formation of voids, which increased
with increasing EFB filler content. The density of the composites, however, still
increased with increasing filler content because the effect of voids was less significant
than the effect of an increase in filler content.
Theoretical
1.428
1.427
1.426
Density (g/cm3)
1.424
1.422
1.425
1.423
1.422
1.420
1.426
1.421
1.419
1.418
1.417
1.415
1.416
Experimental
1.414
1.412
1.411
1.410
1.408
0
10
20
30
40
Filler content (phr)
Figure 3.7
The theoretical and experimental densities of EFB-filled composites
(S9 - S12) with respect to EFB filler contents
50
92
Void at fibre-matrix interface
Figure 3.8
SEM micrograph of impact-fractured surface of S11 (Magnification
2000x)
3.3.2 Mechanical Properties
This section discusses the impact strength and flexural properties of the
composites with respect to filler content, impact modifiers concentration, and
coupling agent-treated filler content. The size of EFB filler incorporated into PVC-U
matrix was less than 75 µm. Two types of impact modifier used were acrylic and
CPE. The effect of other fillers such as NPCC and extracted filler on the impact
strength and flexural properties was also investigated as a minor part of this study.
Tensile properties are important parameters of composites, however, in structural
applications frequently involve flexural and impact stress modes. Therefore, only
flexural and impact properties were investigated.
3.3.2.1 Notched Izod Impact Strength
The impact strength represents the amount of energy that can be absorbed by a
material when subjected to sudden load before failure occurs. The influence of EFB
93
filler, acrylic, and CPE impact modifier contents on the impact strength is discussed
in this section.
A.
Impact Modified PVC-U Compounds
Table 3.4 shows the impact strength of impact-modified PVC-U compounds at
various contents of acrylic and CPE impact modifier. The result of unmodified PVCU (S0) was included as a comparison. The impact strength of impact-modified
compounds rapidly increased when 3 phr impact modifier added in PVC-U and
increased continuously as the impact modifier content increased from 3 to 12 phr.
This is typical of toughened plastics containing impact modifier. It can be seen that at
3 phr, acrylic was able to produce approximately 59 % increment in impact strength
of PVC-U, while the CPE gave 57 % increment. It was observed that all samples
containing 3 phr and lower of impact modifier broke completely into two halves
during impact testing.
There were mixtures in the failure mode for the samples containing 6 phr of
both impact modifiers. However, at 9 phr, the samples underwent hinge breaks
(Figure 3.9) i.e. the samples did not break completely. This result suggested that the
brittle-ductile transition occurred at around 6 phr for both the acrylic and CPE impactmodified PVC-U samples. This transition also resulted in the experimental errors at 6
phr for both impact modifiers as shown in Table 3.4 were higher than other impact
modifier contents. From the number of unbroken samples at 6 phr and impact strength
values at 3 phr, results showed that acrylic was a more effective impact modifier than
CPE at low impact modifier content.
Table 3.4 also shows that the optimum impact strength of acrylic-impact
modified compound occurred at 9 phr. This is because the impact strength was
relatively constant with further increased to 12 phr. However, the impact strength of
CPE-impact modified compound kept increasing with increasing CPE content, even
94
though at 9 phr all the samples underwent hinge breaks. The difference in the
effectiveness (optimum proportion) showed that the toughening mechanism of both
impact modifiers was definitely different (Robinovic, 1983; Hiltner et al., 1984; Lutz,
1993).
The difference in the effectiveness of both impact modifiers can be observed
at the impact-fractured surface of the samples. SEM micrographs in Figure 3.10
shows that the failure modes of impact-fractured surface of S0 which is brittle in
nature. However, as shown in Figures 3.11 and 3.12, the addition of impact modifier
transformed the brittle mode of fracture surface to the ductile mode, where the
impact-fractured surface of impact-modified compound was smoother than
unmodified ones. For impact-modified compounds, the impact fractured surface of
acrylic-impact modified (Figure 3.11) was smoother than CPE-impact-fractured
surface (Figure 3.12). It indicates that the acrylic is more effective in enhancing
impact strength of compound compared to CPE.
Table 3.4: Effect of impact modifiers content on the impact strength of PVC-U
compounds
S0
Acrylic-Impact Modified
Complete
Impact
Broken
Strength
(no. of
2
(kJ/m )
sample)
8.04 + 0.85
7
S0
CPE-Impact Modified
Complete
Impact
Broken
Strength
(no. of
2
(kJ/m )
sample)
8.04 + 0.85
7
S1
19.65 + 1.81
7
S5
18.55 + 0.70
7
S2
93.13 + 30.30
3
S6
48.60 + 41.44
5
S3
109.53 + 5.99
0
S7
99.60 + 11.10
0
S4
109.03 + 4.23
0
S8
119.58 + 3.80
0
Sample
Sample
95
Figure 3.9
Hinge breaks of impact-modified PVC-U samples (S3)
According Hiltner et al. (1984), the most effective effect in impact
modification of rigid polymers was when the rubbery impact modifier dispersed in the
polymeric matrix as discrete small particles. The ability of the discrete small particles
of acrylic to well disperse in the continuous matrix was contributed to the better effect
on the impact strength of acrylic-impact modified compound. This is clearly not the
case for CPE-impact modified compound where the discrete particles of CPE have
only a very small effect on the impact strength compared to that achieved by a
continuous network of CPE (Hiltner et al., 1984).
96
Figure 3.10
SEM micrograph of impact-fractured surface of S0 (Magnification
200x)
Figure 3.11
200x)
SEM micrograph of impact-fractured surface of S3 (Magnification
97
Figure 3.12
SEM micrograph of impact-fractured surface of S7 (Magnification
200x)
B.
EFB-Filled Impact-Modified PVC-U Composites
Figures 3.13 and 3.14 show that with increasing EFB filler contents, the
impact strength of both unmodified and impact-modified EFB-filled composites
decreased gradually. This observation was expected for filled composites and has also
been reported by other researchers (Raj et al., 1990; Zaini et al., 1996; Ismail and
Mega, 2001). Furthermore, as shown by the impact-fractured surface of composites
in Figures 3.15 through 3.18, the incorporation of EFB filler into PVC-U matrix
reduced the ductile behaviour of the matrix by making the composites more brittle.
98
14
2
Impact strength (kJ/m )
13
0 phr
3 phr
12
11
6 phr
9 phr
12 phr
10
9
8
7
6
5
0
10
20
30
40
50
Filler content (phr)
Figure 3.13
Effect of filler content on the impact strength of EFB-filled
composites (S9-S12) and EFB-filled acrylic-impact modified composites (S13-S28)
0 phr
3 phr
13
2
Impact strength (kJ/m )
12
6 phr
9 phr
12 phr
11
10
9
8
7
6
5
0
10
20
30
40
50
Filler content (phr)
Figure 3.14
Effect of filler content on the impact strength of EFB-filled
composites (S9-S12) and EFB-filled CPE-impact modified composite (S29- S44)
99
Figure 3.15
SEM micrograph of the impact-fracture surface of composite
incorporated with 10 phr filler (Magnification 500x)
Figure 3.16
SEM micrograph of the impact-fracture surface of composite
incorporated with 20 phr filler (Magnification 500x)
100
Figure 3.17
SEM micrograph of the impact-fractured surface of composite
incorporated with 30 phr filler (Magnification 500x)
Filler bundle
Figure 3.18
SEM micrograph of the impact-fractured surface of composite
incorporated with 40 phr filler (Magnification 500x)
Table 3.5 shows the percentage of impact strength reduction of composites
increased as the filler content increased from 10 to 40 phr. The percentage of
reduction of the EFB-filled acrylic-impact modified composites (S13-S28) was higher
101
than EFB-filled CPE-impact modified composites (S29-S44). The results indicated that
the impact strength of S13-S28 was higher at 10 phr but lower at 40 phr compared to
S29-S44. This means that the acrylic was efficient in enhancing the impact strength of
composites at low filler content while CPE was efficient at high filler content. Table
3.5 also shows that EFB-filled composites (S9-S12) have the lowest percentage of
reduction (20 %) due to their lowest impact strength values at all filler contents
compared to S13-S28 and S29-S44.
Table 3.5: Percentage of impact strength reduction of EFB-filled impact-modified
composites as filler content increased from 10 to 40 phr
Impact modifier content
(phr)
0
Impact strength reduction (%)
EFB-filled acrylic-impact EFB-filled CPE-impact
modified composites
modified composites
20
20
3
36
17
6
45
37
9
42
39
12
49
36
There are several reasons why the impact performance of composites
decreased as the filler content increased. Firstly, there is the detrimental effect of the
fillers caused by the volume they take up. Fillers, unlike the matrix, are incapable of
dissipating stress through the mechanism known as shear yielding prior to fracture.
They may also hinder the local chain motions of the polymer molecules to shear yield
(Stevenson, 1995). As a result, the ability of the composites to absorb energy during
fracture propagation decreased. Figures 3.10 and 3.15-3.18 clearly showed that the
impact fractured surface of composites changed from smooth to rough as the filler
content increased from 0 to 40 phr. In other words, the ductile portion contributed by
PVC-U matrix reduced, and the failure mode became more brittle as the filler content
increased.
102
Secondly, composites materials with satisfactory mechanical properties can
only be achieved if there is good dispersion and wetting of the fillers in the matrix,
giving rise to strong interfacial adhesion. However, this is not the case when EFB
fillers are used in PVC. Although the polarity of EFB fillers made them capable of
forming a physical interaction with polar PVC (Figure 3.19), it was relatively weak
interaction compared to the strong filler-filler interaction caused by hydrogen
bonding. Therefore, EFB fillers had a greater tendency to agglomerate among
themselves into filler bundles, which consequently, lowered the area of contact with
the matrix. This can be explained with the aid of the SEM micrographs shown in
Figures 3.17-3.18. The EFB fillers tended to cling together in bundles and to resist
dispersion as the filler content increased. The filler bundles can be observed in the
SEM micrograph distributing unevenly throughout the matrix.
H
H
C
C
δ+H
O
-
δ
O
-
H
H
Cl δ
+
Hδ
C
C
OH
O
HOH2C
δ
+
δ
Cl
δO
+
Hδ
δ+
H
OH
Cellulose
O
HOH2C
PVC
C
-
OH
O
O
Figure 3.19
H
H
C
C
-
δ Cl δ
H
δδ+
O
H
+
H
H
O
O
HOH2C
Polar-polar interactions between PVC molecule and cellulose molecule
The presence of moisture as mentioned in Section 3.3.1 might interfere with
the physical bonding between fillers and PVC, and potentially acted as a lubricant at
the filler-matrix interface (Mengeloglu, 2001; Sombatsompop et al., 2004). The
presence of moisture in the composites was also detected in the DTG curves for all
composites as mentioned in Chapter 5. Other researchers had also detected the
moisture content in the composites, even though careful care had been taken prior to
drying of cellulose before mixing (Sapieha et al., 1989; Thiebaud et al., 1997; Peters
and Bruch, 2001). This moisture was also able to vaporize during composite
103
preparation to form a number of small voids in the PVC matrix. The presence of voids
in the matrix might also become the potential sites for crack initiation. These factors
increased the weakness of interfacial adhesion between the filler and the matrix, and
became the potential sites for crack growth as the inability of fillers to support the
stress transfer from the polymer matrix decreased (Rozman et al., 1998). As shown in
Figures 3.20 and 3.21, the weakness of interfacial adhesion resulted in debonding and
pulled of filler bundles in the composites.
Filler debonding
Figure 3.20
SEM micrograph of filler debonding on the impact-fractured surface of
composite incorporated with 30 phr filler of S11 (Magnification 900x)
104
Fillers pulled-out
areas
Figure 3.21
SEM micrograph of filler bundles pulled-out area on the impact-
fractured surface composite incorporated with 30 phr filler of S11 (Magnification
1000x)
The toughening of composites by introducing impact modifiers was also
investigated. Figures 3.22 and 3.23 show the impact strength of the impact-modified
composites improved with increasing impact modifier content.
Without impact
modification, the deleterious effect of incorporating EFB fillers to the PVC-U matrix
was apparent because unmodified composites exhibited a much lower capability for
absorbing impact energy. For instance, the impact strength of composite filled with 10
phr filler (7.1 kJ/m2) was inferior compared to that of PVC-U compound (8.0 kJ/m2).
105
2
Imapct Strength (kJ/m )
14
10 phr
20 phr
12
30 phr
40 phr
10
8
6
4
0
Figure 3.22
3
6
9
Acrylic content (phr)
12
15
Effect of acrylic content on the impact strength of EFB-filled acrylic-
impact modified composites (S0-S4 and S9-S28)
13
2
Impact strength (kJ/m )
12
11
10 phr
10
20 phr
30 phr
9
40 phr
8
7
6
5
4
0
Figure 3.23
3
6
9
CPE content (phr)
12
15
Effect of CPE impact modifier content on the impact strength of EFB-
filled CPE-impact modified composites (S5 -S8 and S29-S44)
106
The lowering of impact strength of composites due to incorporation of EFB
filler was well recovered by the introduction of impact modifiers into the composites.
Impact modifiers have the capability to compensate the detrimental effect caused by
the filler that is lowering the yield stress of PVC-U matrix. Therefore, PVC-U matrix
was able to undergo shear yielding rather than fracture when subjected to sudden load.
Through this mechanism, the composites were able to suppress catastrophic failure
(brittle failure). As a result, the enhancement of impact strength with increasing
impact modifier content was expected. Mengeloglu (2001) has also reported a similar
result, in which the addition of impact modifiers efficiently reduced brittle crack
propagation in the wood flour-filled PVC composite.
It is interesting to observe the effectiveness of the impact modifier in
enhancing the impact strength of EFB-filled composites. Table 3.6 shows that the
percentage of impact strength increment for the composites decreased as the filler
content increased, as the presence of EFB fillers in composites dominated. The results
showed that the ability of both the impact modifiers to compensate the detrimental
effect of filler reduced as the filler content increased. As reported in Table 3.5, the
difference in the effectiveness of both the impact modifiers can also be observed in
Table 3.6. Acrylic is believed to be more effective at low filler content, whereas CPE
at high filler content. This is due to the discrete acrylic particles were able to disperse
evenly throughout the matrix at low filler contents and effectively improved the
impact strength of composites. However, the dispersion of acrylic particles was
restricted by EFB at high filler contents and thus acrylic unable to improve the impact
strength of composites effectively.
Figure 3.24 illustrates that in general, CPE is more efficient and effective as
impact modifier than acrylic at filler content of 20 phr and higher. Gerlach (1998)
reported the similar advantage of CPE at higher filler content. The plausible reason
for this observation is the adhesion between filler and matrix might be improved by
the addition of CPE. It may be elucidated in terms of polarity between hydroxyl (OH)
groups on the EFB filler surface and chlorine (Cl) atoms of PVC resin. The addition
of CPE impact modifier, which contains 36 % of Cl atoms, into the PVC resin may
107
increase the Cl content and polarity of CPE-impact modified PVC-U. Because of that,
the physical interaction between OH groups and Cl atoms took place and
consequently produced better wetting of filler surface by PVC-U matrix. Therefore,
the filler-matrix adhesion of composite was improved.
Table 3.6: Percentage of impact strength increment for EFB-filled impact-modified
composites as the impact modifier content increased from 0 to 12 phr
EFB filler content (phr)
10
Impact strength increment (%)
EFB-filled acrylic-impact EFB-filled CPE-impact
modified composites
modified composites
78
69
20
37
38
30
31
51
40
14
35
16.0
10 phr
14.0
20 phr
30 phr
40 phr
2
Impact Strength (kJ/m )
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Acrylic- CPE3 phr
3 phr
Figure 3.24
Acrylic- CPE6 phr
6 phr
Acrylic9 phr
CPE9 phr
Acrylic- CPE12 phr 12 phr
Effects of acrylic and CPE impact modifier on the impact strength of
EFB-filled impact-modified composites
108
3.3.2.2 Flexural Properties
Flexural strength is the ability of a material to withstand bending forces
applied perpendicular to its longitudinal axis. Flexural modulus is a measure of
stiffness during the first or initial part of the bending process. Similar to the section on
impact strength, the influences of EFB filler, acrylic and CPE impact modifier
contents on the flexural properties of the composites will be discussed in this section.
A.
Impact Modified PVC-U Compounds
Figures 3.25 and 3.26 show the effect of acrylic and CPE impact modifiers on
the flexural properties of impact-modified compounds. While the impact strength was
improved, the flexural properties were adversely affected by the addition of acrylic
and CPE. As the impact modifier contents increased from 0 to 12 phr, acrylic
generated 28 % and 22 % decrement in flexural modulus and flexural strength of
PVC-U, respectively, while CPE caused 29 % and 31 % decrement in flexural
modulus and flexural strength, respectively. The rubbery phase introduced by the
impact modifiers decreased both the stiffness and flexural strength of the compounds.
This was probably due to the softening effect generated by the impact modifier, which
lowered the yield stress, thereby increasing the energy absorption and consequently
lowered the modulus and strength of the PVC-U compound. In other words, impact
modifier increased the local chain motion of the PVC molecules that enabled them to
shear yield. Several researchers also reported that the flexural properties of PVC
modified with impact modifiers decreased as the impact modifier contents increased
(Deani et al., 1986; Lutz, 1993; Wimolmala et al., 2001).
109
Flexural modulus (MPa)
3800
Acrylic
3600
CPE
3400
3200
3000
2800
2600
2400
0
3
6
9
12
Impact modifier content (phr)
Figure 3.25
Effect of impact modifiers content on the flexural modulus of impact
modified compounds (S0-S8)
Flexural strength (MPa)
90.0
Acrylic
85.0
80.0
CPE
75.0
70.0
65.0
60.0
55.0
50.0
45.0
40.0
0
Figure 3.26
3
6
9
Impact modifier content (phr)
12
Effect of impact modifiers content on the flexural strength of impact
modified compounds (S0-S8)
110
Although the flexural properties decreased linearly with increasing impact
modifier contents, the flexural properties of acrylic-impact modified PVC-U
compound were found higher than CPE-impact modified PVC-U compound. This
result indicates that acrylic which comprised a PBA core and a PMMA shell has less
softening effect than CPE for two possible reasons. The first reason being that the
PMMA shell had higher stiffness and was more compatible with PVC matrix. The
compatibility between impact modifier and matrix has resulted in the reduction in free
volume of matrix, which increased the modulus of compound (Wimolmala et al.,
2001). Besides that, compatibility also provided good interfacial bonding between the
phases to allow efficient stress transfer and thus enhanced the flexural properties of
acrylic-impact modified compounds. Secondly, PBA rubber core formed separate
domains and do not soften the PVC matrix whereas CPE was soft and flexible and
was also less compatible in the PVC matrix, thus softening it more aggressively
(Deanin and Chuang, 1986).
B.
EFB-Filled Impact-Modified PVC-U Composites
The flexural modulus increased whereas the flexural strength decreased for all
composites as the filler content increased. The influence of filler content on the
flexural properties of the composites is shown in Figures 3.27-3.30. Modulus or the
material stiffness increased significantly with increasing filler content for all
composites.
As highlighted by other researchers, the enhancement of modulus
depends on a number of factors, such as filler aspect ratio, filler modulus, and filler
content. This result indicates that even though EFB fillers have a low aspect ratio
(5:1), they are able to impart a significant improvement in stiffness by hindering the
movement of PVC molecules (Woodhams et al., 1984). The fact that the modulus
increased while the strength decreased with increasing filler content was in agreement
with the trend observed in other fibre-filled thermoplastics (Rozman et al., 2003).
As discussed in the impact strength section, agglomeration of fillers in the
matrix, moisture pick-up in the fillers and interfacial defects could be the causes of
111
the reduction in flexural strength (Figures 3.28 and 3.30). Furthermore, the irregular
shape and a relatively low aspect ratio of EFB filler increased the inability of fillers to
support the stress transmitted from the polymer matrix. This effect is amplified when
the proportion of EFB filler increased (Ichazo et al., 2000; Rozman et al., 2000). A
similar result has been reported for works on the cellulose-filled polymer composites
(Raj et al., 1990; Rozman et al., 1998; Azman Hassan and Sivaneswaran, 2001).
Flexural modulus (MPa)
5000
0 phr
3 phr
6 phr
9 phr
12 phr
4500
4000
3500
3000
2500
2000
0
10
20
30
40
Filler content (phr)
Figure 3.27
Effects of filler and acrylic content on the flexural modulus of EFB-
filled acrylic-impact modified composites (S9-S28)
112
Flexural strength (MPa)
100.0
0 phr
3 phr
6 phr
9 phr
12 phr
90.0
80.0
70.0
60.0
50.0
40.0
0
10
20
30
40
Filler content (phr)
Figure 3.28
Effects of filler and acrylic content on the flexural strength of EFB-
filled acrylic-impact modified composites (S9-S28)
5000
0 phr
3 phr
6 phr
9 phr
12 phr
Flexural modulus (MPa)
4500
4000
3500
3000
2500
2000
0
10
20
30
40
Filler content (phr)
Figure 3.29
Effects of filler and CPE content on the flexural modulus of EFB-
filled CPE-impact modified composites (S29-S44)
113
100.0
0 phr
3 phr
6 phr
9 phr
12 phr
Flexural strength (MPa)
90.0
80.0
70.0
60.0
50.0
40.0
0
10
20
30
40
Filler content (phr)
Figure 3.30
Effects of filler and CPE content on the flexural strength of EFB-filled
CPE-impact modified composites (S29-S44)
Tables 3.7 and 3.8 show the percentage of modulus increment and the
percentage of flexural strength reduction, respectively, for the unmodified and impact
modified composites as the filler contents increased from 0 to 40 phr. It can be seen
that the percentage of modulus increment for EFB-filled composites (S9-S12), EFBfilled acrylic-impact modified composites (S13-S28), and EFB-filled CPE-impact
modified composites (S29-S44) was relatively similar. The result reveals that all
composites underwent a similar degree of increment as the filler contents increased.
On the other hand, the percentage of flexural strength reduction of S13-S28 was higher
than S29-S44. This is due to the flexural strength values of S13-S28 were higher than
S29-S44 at 0 phr and relatively similar at 40 phr of filler. As mentioned earlier in
Section 3.3.2.2 A, the softening effect aggressively generated by CPE compared to
that by acrylic resulted in the flexural strength of S29-S44 was lower than S13-S28.
114
Table 3.7: Percentage of flexural modulus increment for EFB-filled impact modified
composites as the filler content increased from 0 to 40 phr
Impact
modifier
content
(phr)
0
Flexural modulus increment (%)
EFB-filled acrylic-impact
modified PVC-U composites
EFB-filled CPE-impact
modified PVC-U composites
22
22
3
24
22
6
26
21
9
24
27
12
25
24
Table 3.8: Percentage of flexural strength reduction for EFB-filled impact modified
composites as the filler content increased from 0 to 40 phr
Impact
modifier
content
(phr)
0
Flexural strength reduction (%)
EFB-filled acrylic-impact
modified PVC-U composites
EFB-filled CPE-impact
modified PVC-U composites
18
18
3
26
15
6
16
16
9
21
12
12
20
11
Figures 3.31-3.34 show that the flexural properties of composites reduced
significantly as the impact modifiers contents increased from 0 to 12 phr. As
mentioned previously, the softening effect introduced by the impact modifier was the
main factor, which resulted in the reduction of flexural properties. Figures 3.31 and
3.33 show that this effect on the flexural modulus became less significant as the filler
content in the impact modified composites increased. This was due to the separation
among the impact modifier particles increased and thus reduced the effectiveness of
impact modifier to soften the matrix. As a result, composites containing 40 phr filler
115
produced the highest values of modulus as the impact modifier content increased form
0 to 12 phr. Meanwhile, in case of flexural strength, the adverse effect was observed.
The flexural strength of composites at 40 phr with the increase of impact modifier
content from 0 to 12 phr has the lowest series of value (Figures 3.32 and 3.34). The
possible factors severely affected the flexural strength of the composites were the
weak filler-matrix interface, and agglomeration and randomly dispersed fillers.
5000
0 phr
10 phr
20 phr
30 phr
40 phr
Flexural Modulus (MPa)
4500
4000
3500
3000
2500
2000
0
3
6
9
12
Acrylic content (phr)
Figure 3.31
Effects of filler and acrylic content on the flexural modulus of EFB-
filled acrylic-impact modified composites (S13-S28)
116
Flexural strength (MPa)
100.0
0 phr
10 phr
20 phr
30 phr
40 phr
90.0
80.0
70.0
60.0
50.0
40.0
0
3
6
9
12
Acrylic content (phr)
Figure 3.32
Effects of filler and acrylic content on the flexural strength of EFB-
filled acrylic-impact modified composites (S13-S28)
Flexural modulus (MPa)
5000
0 phr
4500
10 phr
20 phr
30 phr
40 phr
4000
3500
3000
2500
2000
0
Figure 3.33
3
6
CPE content (phr)
9
12
Effects of filler and CPE content on the flexural modulus of EFB-filled
CPE-impact modified composites (S29 -S44)
117
100.0
0 phr
10 phr
20 phr
30 phr
40 phr
Flexural strength (MPa)
90.0
80.0
70.0
60.0
50.0
40.0
0
6
3
9
12
CPE content (phr)
Figure 3.34
Effects of filler and CPE content on the flexural strength of EFB-filled
CPE-impact modified composites (S29 - S44)
Tables 3.9 and 3.10 show the percentage of flexural modulus and flexural
strength reduction, respectively.
Table 3.9 shows that the degree of modulus
reduction for both acrylic-impact modified and CPE-impact modified filled
composites was relatively similar as the impact modifier contents increased from 0 to
12 phr.
Meanwhile, Table 3.10 shows that the percentage of flexural strength
reduction of EFB-filled CPE-impact modified composites was higher than EFB-filled
acrylic-impact modified composites. This is due to the softening effect aggressively
generated by CPE compared to that by acrylic.
118
Table 3.9: Percentage of flexural modulus reduction for EFB-filled impact modified
composites as the impact modifier increased from 0 to 12 phr
EFB filler
content
(phr)
0
Flexural modulus reduction (%)
EFB-filled acrylic-impact
EFB-filled CPE-impact
modified composites
modified composites
28
28
10
29
28
20
27
27
30
24
26
40
26
27
Table 3.10: Percentage of flexural strength reduction for EFB-filled impact modified
composites as the impact modifier increased from 0 to 12 phr
EFB filler
content
(phr)
0
Flexural strength reduction (%)
EFB-filled acrylic-impact
EFB-filled CPE-impact
modified composites
modified composites
22
31
10
34
35
20
30
32
30
29
36
40
24
25
Based on Figures 3.35 and 3.36, the effect of both impact modifiers on the
flexural properties of the composites can be compared. Due to the softening effect
aggressively generated by CPE, thus EFB-filled CPE-impact modified PVC-U
composites have lower values of flexural properties compared to the EFB-filled
acrylic-impact modified PVC-U composites.
119
5000
0 phr
Flexural modulus (MPa)
4500
10 phr
20 phr
30 phr
40 phr
4000
3500
3000
2500
2000
1500
1000
500
0
Acrylic-3 CPE- 3 Acrylic-6 CPE- 6 Acrylic-9 CPE- 9 Acrylic- CPEphr
phr
phr
phr
phr
phr
12 phr 12 phr
Effects of acrylic and CPE impact modifier on the flexural modulus of
Figure 3.35
EFB-filled impact modified composites
100
Flexural strength (MPa)
90
0 phr
10 phr
20 phr
30 phr
40 phr
80
70
60
50
40
30
20
10
0
Acrylic- CPE- Acrylic- CPE- Acrylic- CPE- Acrylic- CPE3 phr
3 phr 6 phr
6 phr
9phr
9 phr 12 phr 12 phr
Figure 3.36
Effects of acrylic and CPE impact modifier on the flexural strength of
EFB-filled impact modified composites
120
3.3.2.3 EFB-Filled Acrylic-Impact Modified PVC-U Composites Treated With
Coupling Agents
The purpose of adding coupling agents to the composites is to improve the
interfacial adhesion bond strength and wetting of the filler by the matrix. The purpose
of this study is to investigate whether coupling agents would lead to any improvement
in the impact properties of composites or vice versa. The coupling agents were only
applied to the EFB-filled PVC-U composites and EFB-filled acrylic-impact modified
PVC-U composites. As mentioned earlier in Section 3.2.4, the blend formulations
used in this study are based on the PVC window profile formulation, which is suitable
for outdoor applications, mainly for blend formulations added with acrylic impact
modifier. This is because the acrylic is reported more weather resistance compared to
CPE (Robinovic, 1983). Therefore, the acrylic-impact modified composites are only
used for coupling agents treatment.
A.
Impact Strength
Figures 3.37 and 3.38 show that the impact strength of EFB-filled and EFB–
filled acrylic-impact modified composites, respectively, was generally higher
compared to those that were not treated with Prosil 9234 and NZ 44 coupling agent.
Both coupling agents were able to enhance the impact strength of the composites by
means of improving the filler-matrix adhesion.
121
20.0
18.0
10 phr
16.0
20 phr
30 phr
40 phr
Impact strength (kJ/m2)
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil0 phr treated
Figure 3.37
3 phr treated 6 phr treated
9 phr treated
12 phr treated
Effects of EFB filler and acrylic content on the impact strength of
EFB-filled acrylic-impact modified composites treated with Prosil 9234 (S49-S68)
16.0
14.0
10 phr
20 phr
30 phr
40 phr
2
Impact strength (kJ/m )
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Acrylic-NZ 44- Acrylic-NZ 44- Acrylic-NZ 44- Acrylic-NZ 44-Acrylic-NZ 440 phr treated 3 phr treated
Figure 3.38
6 phr treated 9 phr treated 12 phr treated
Effects of EFB filler and acrylic content on the impact strength of
EFB-filled acrylic-impact modified composites treated with NZ 44 (S69-S88).
122
As mentioned in Section 2.4.3.1 (Chapter 2), the reaction of the tetrafunctional organo-metallic compounds based on silicone and zirconium was believed
to have occurred in two steps (Ahmad Fuad et al., 1997). First, the alkoxy groups in
the coupling agent underwent hydrolysis process. Water from the hydrolysis might
come from the surface humidity of filler (in case of the Prosil 9234 treatment), and
from the surface or in the PVC resin (in the case of NZ44 treatment) (Ahmad Fuad et
al., 1997). The hydroxyl groups were supposed to link to EFB filler through the
formation of hydrogen bonds with the hydroxyl groups at the EFB filler surface. Then
Si-O or Zr-O cross-links formed between the filler surface and the adjacent functional
groups via the condensation reaction with the elimination of water. The scheme
reaction in Figure 2.12 (Chapter 2) can be used to describe the reaction of Prosil 9234
with fillers, while that of NZ 44 is shown in Figure 3.39.
Step 1
hydrolis
X-Zr(OR)3
X-Zr(OH)3
Step 2
OH
OH
OH
X-Zr
+ OH
+ OH
O
O
OH
H
OH
H
X-Zr
O
OH
O
Filler surface
X-Zr
OH
OH
OH
Filler surface
X-Zr
H
OH
H
Condensation
OH
X-Zr
OH
OH
Figure 3.39
O
+
O
OH
OH
X-Zr
OH
O
Filler surface
O
Filler surface
O
X-Zr
X-Zr
O
Bonding mechanism of NZ 44 coupling agent to the filler’s surface
123
SEM micrographs of the impact-fractured surface of Prosil 9234 treated-filled
composites (Figures 3.40a-3.40b) and NZ 44 treated-filled composites (Figures 3.40c3.40d) also show that the formation of interaction between treated-filler and matrix
took place in the composites. This is because the treated-fillers pulled out from the
matrix but a fair amount of polymeric residues remained on the fillers. It means that
the matrix wetted the treated fillers in composites extensively. Besides that the treated
fillers in composites in Figures 3.40a and 3.40c show only slight fillers were pulled
out and formed a more topographically even surface compared to fracture surface of
the untreated filler-filled composite in Figure 3.17.
The formation of ether linkage (-O-) or interaction between treated fillers and
coupling agents also shown by the FTIR spectra of both treated EFB-filled composites
in the Figure 3.46 (discuss in detail at part D in this section). The remaining chain of
coupling agents (Figure 3.39) adhered to the PVC with the help of a Van der Waals
type of weak interaction. By this means, coupling agent made a link between EFB
filler and PVC. As a result, the impact strength of treated-filled composites improved
as compared to the untreated ones.
Polymeric residues remained on
the fillers
(a)
124
Polymeric residues remained on
the filler
(b)
(c)
125
Polymeric residues remained on
the fillers
(d)
Figure 3.40
SEM micrographs of the impact fractured-surface of composites (a)
Prosil 9234 treatment (S51) (Magnification 100x) (b) S51 (Magnification 2000x) (c)
NZ 44 treatment (S71) (Magnification 500x) and (d) S71 (Magnification 2000x)
Table 3.11 shows the comparison on the effect of Prosil 9234 and NZ 44 on
the impact strength of composites. It may be worth noted that the performance of both
coupling agents in enhancing the impact strength of composites is difficult to be
distinguished. This is due to the impact strength values obtained in Table 3.11 was
relatively similar except for composites containing 12 phr acrylic at filler contents of
10 phr and 20 phr, whereby in general, the impact strength of composites treated with
Prosil 9234 was higher than composites treated with NZ 44 coupling agent. This may
be due to the techniques used for treating the composites with both coupling agents in
this study were different. As reported in Section 3.2.3, Prosil 9234 was used to treat
the EFB fillers surfaces whereas NZ 44 was used to treat the PVC matrix rather than
the fillers. Both techniques, the filler surface treatment and matrix resin treatment,
were reported to improve the interaction between fibres and matrix at the interface
regions in the composites (Maldas et al., 1991). However, the results show that the
treatment of fillers, which alters the chemical nature of fillers surfaces, has been
considered to be more promising method in enhancing the filler-matrix interaction
compared to the matrix treatment (Maldas et al., 1990). As a result, Prosil 9234 has
brought a slight higher improvement in the impact strength compared to the
126
composites treated with NZ44.
The effectiveness of Prosil 9234 has also been
reported by Ahmad Fuad et al. (1997) who used these two types of coupling agents in
the rice husk ash-polypropylene composites.
Table 3.11: Impact strength of EFB –filled acrylic-impact modified composites
treated with Prosil 9234 and NZ 44
Filler
0
0
Content Prosil
NZ44
(phr)
9234
7.7
7.7
10
+
+
0.6
0.6
7.0
6.9
20
+
+
0.5
0.4
6.3
6.3
30
+
+
0.4
0.5
5.7
5.7
40
+
+
0.6
0.6
B.
Acrylic Impact Modifier Content (phr)
3
3
6
6
9
9
12
12
Prosil
Prosil
Prosil
Prosil
NZ44
NZ44
NZ44
NZ44
9234
9234
9234
9234
9.4
9.4
9.1
11.3
11.4
11.4
15.9
11.9
+
+
+
+
+
+
+
+
0.9
0.9
0.4
1.3
0.9
1.4
2.5
0.3
7.1
7.7
7.9
8.0
8.6
9.0
9.7
8.8
+
+
+
+
+
+
+
+
0.5
0.5
0.3
0.4
0.4
0.6
0.2
0.9
6.6
6.8
7.2
7.0
7.5
7.4
7.6
7.5
+
+
+
+
+
+
+
+
0.3
0.8
0.3
0.4
0.6
0.3
0.5
0.3
6.6
6.4
6.7
6.5
6.9
6.6
7.0
6.9
+
+
+
+
+
+
+
+
0.6
0.4
0.2
0.3
0.4
0.4
0.3
0.3
Flexural Properties
Figures 3.41-3.44 show that the addition of both coupling agents improved the
flexural properties, particularly for the flexural modulus of composites. This is
because the coupling agents were able to enhance the interfacial adhesion between
filler and matrix. It could be also that the initially strong filler-filler interaction caused
by the intermolecular hydrogen bonding has also been weakened, which leads to the
better dispersion of fillers in the matrix.
The flexural modulus of composites treated with coupling agents improved
significantly as shown by Figures 3.41 and 3.43. Although these two coupling agents
127
were able to enhance the stiffness of the composites, the flexural modulus (Table
3.12) indicates that Prosil 9234 has brought a greater stiffness to composites than
composites treated with NZ44. Similar results on the stiffness improvement of sisal
fibre reinforced polystyrene composites upon treatment with benzoyl chloride have
been reported (Manikandan Nair et al., 1996).
6000
10 phr
20 phr
30 phr
40 phr
50003.32: Effect of EFB filler and acrylic content on the flexural modulus of EFBFigure
Flexural modulus (MPa)
filled acrylic-impact modified PVC-U composites treated with Prosil 9234 coupling
4000
agent (S9 to S28 and S49 to S68).
3000
2000
1000
0
Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil0 phr treated
Figure 3.41
3 phr treated 6 phr treated 6 phr treated 12 phr treated
Effect of EFB filler and acrylic contents on the flexural modulus of
EFB-filled acrylic-impact modified composites treated with Prosil 9234 (S9-S28 and
S49-S68)
128
100.0
10 phr
90.0
20 phr
30 phr
40 phr
Flexural strength (MPa)
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil- Acrylic- Prosil- Acrylic Prosil0 phr treated
3 phr treated
6 phr treated
9 phr treated 12 phr treated
Figure 3. 42 Effect of EFB filler and acrylic contents on the flexural strength of
EFB-filled acrylic-impact modified composites treated with Prosil 9234 (S9-S28 and
S49-S68)
6000
10 phr
20 phr
30 phr
40 phr
Flexural modulus (MPa)
5000
4000
3000
2000
1000
0
Acrylic-NZ44- Acrylic- NZ44- Acrylic-NZ44- Acrylic-NZ44- Acrylic- NZ440 phr treated
Figure 3.43
3 phr treated
6 phr treated
9 phr treated 12 phr treated
Effect of EFB filler and acrylic contents on the flexural modulus of
EFB-filled acrylic-impact modified composites treated with NZ44 (S9-S28 and S69-S88)
129
100.0
10 phr
90.0
20 phr
30 phr
40 phr
Flexural strength (MPa)
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Acrylic- NZ44- Acrylic- NZ44- Acrylic- NZ44- Acrylic- NZ44- Acrylic- NZ440 phr treated
Figure 3.44
3 phr treated
6 phr treated
9 phr treated 12 phr treated
Effect of EFB filler and acrylic content on the flexural strength of
EFB-filled acrylic-impact modified composites treated with NZ44 (S9-S28 and S69-S88)
Based on the flexural strength values of composites as shown in Table 3.13,
both coupling agents have a similar ability in enhancing the flexural strength of
composites. However, in general, Prosil 9234 showed slightly better ability in
enhancing the flexural strength of composites compared to NZ44. Although NZ 44
has a similar purpose as Prosil 9234 to impart a better wetting, dispersion and
interaction, the flexural modulus (Table 3.12) and flexural strength (Table 3.13)
showed that Prosil 9234 was more effective than NZ 44. It indicates that NZ 44
insufficient to form a strong bridge between filler and matrix at the interface regions
in the composites. On the other hand, Prosil 9234 capable to generate a strong bonds
with fillers to give a better performance of the composites (Wu et al., 2000).
130
Table 3.12: Flexural modulus of EFB–filled acrylic-impact modified composites
treated with Prosil 9234 and NZ 44
EFB
Filler
0
Content Prosil
(phr)
9234
4196
+
10
80
4208
20
+
72
4475
30
+
252
4636
40
+
150
Acrylic Impact Modifier Content (phr)
3
3
6
6
9
9
12
12
Prosil
Prosil
Prosil
Prosil
NZ44
NZ44
NZ44
NZ44
NZ44
9234
9234
9234
9234
3859 3583 3481 3573 3302 3145 3007 2910 2766
+
+
+
+
+
+
+
+
+
91
69
122
218
90
84
41
81
31
4272 4041 3823 3605 3574 3566 3172 3196 3058
+
+
+
+
+
+
+
+
+
147
67
97
61
51
182
99
74
38
4505 4252 4111 3774 3823 3632 3451 3306 3287
+
+
+
+
+
+
+
+
+
161
68
32
59
139
110
91
94
89
4698 4426 4362 4103 3965 3804 3729 3571 3392
+
+
+
+
+
+
+
+
+
196
181
63
93
92
79
83
168
42
0
Table 3.13: Flexural strength of EFB–filled acrylic-impact modified composites
treated with Prosil 9234 and NZ 44
EFB
Filler
0
Content Prosil
(phr)
9234
84.9
10
+
3.0
82.2
20
+
4.3
72.9
30
+
3.1
67.2
40
+
7.5
Acrylic Impact Modifier Content (phr)
3
3
6
6
9
9
12
12
Prosil
Prosil
Prosil
Prosil
NZ44
NZ44
NZ44
NZ44
NZ44
9234
9234
9234
9234
85.0
78.6
73.9
74.0
68.2
65.0
64.4
62.8
59.8
+
+
+
+
+
+
+
+
+
2.4
2.1
1.9
1.7
1.9
1.6
2.9
1.7
1.7
77.7
79.9
67.8
70.9
70.3
65.3
58.5
59.3
53.7
+
+
+
+
+
+
+
+
+
6.4
1.9
3.5
3.0
1.6
6.1
1.6
3.1
3.2
76.5
69.6
64.2
60.0
63.6
55.3
55.8
55.3
52.0
+
+
+
+
+
+
+
+
+
4.8
5.0
1.3
3.4
2.3
3.2
1.0
4.4
1.2
69.8
62.3
60.7
57.9
63.4
51.4
51.8
51.0
50.3
+
+
+
+
+
+
+
+
+
7.3
2.7
4.7
5.0
2.6
2.0
1.6
4.0
3.6
0
131
C.
Relative Modulus of Composites
A number of models have been used to calculate the relative modulus of
composites. The most commonly used was discussed in the Chapter 2. It was found
that the relative elastic modulus (Ec/Ep) of the composites varied with volume
fraction, φf as shown in Tables 3.14-3.18. The relative elastic modulus of untreated
and treated composites increased with increasing volume fractions. The modulus
values of treated composites were higher than modulus of untreated ones. These
tables also show the comparison between the experimental relative modulus values
and the predicted relative modulus values obtained from the predictive models, which
take into account the shape, packing fraction, and adhesion between the filler and
matrix polymer.
Table 3.14: Comparison between the predicted and the experimental of relative
modulus of composites
EFB-Filled Composites
Experimental Values
EFB
(phr)
φ
f
10
Predicted Values
Einstein
Kerner
(perfect
adhesion
Untreated
(S9 - S12)
Prosil 9234
(S49 -S52)
NZ44
(S69 - S72)
Einstein
(without
adhesion)
0.08
1.07
1.20
1.08
1.08
1.20
1.19
1.07
20
0.15
1.15
1.20
1.18
1.15
1.38
1.39
1.14
30
0.21
1.18
1.28
1.23
1.21
1.53
1.59
1.19
40
0.27
1.29
1.32
1.26
1.27
1.68
1.83
1.24
LewisNielsen
132
Table 3.15: Comparison between the predicted and the experimental of relative
modulus of filled acrylic-impact modified composites at 3 phr of acrylic
EFB-Filled Acrylic-Impact Modified Composites
Experimental Values
Untreated
NZ44
Prosil 9234
(S13 to
(S73 to
(S53 to S56)
S16)
S76)
Predicted Values
Einstein
Kerner
(perfect
adhesion)
EFB
(phr)
φ
f
10
0.08
1.08
1.11
1.08
1.08
1.20
1.19
1.07
20
0.15
1.18
1.26
1.19
1.15
1.38
1.39
1.14
30
0.21
1.23
1.32
1.28
1.21
1.53
1.59
1.19
40
0.26
1.26
1.38
1.36
1.26
1.65
1.78
1.23
Einstein
(without
adhesion)
LewisNielsen
Table 3.16: Comparison between the predicted and the experimental of relative
modulus of filled acrylic-impact modified composites at 6 phr of acrylic
EFB
(phr)
EFB-Filled Acrylic-Impact Modified Composites
Experimental Values
Predicted Values
Einstein
Einstein
Untreated Prosil 9234
NZ44
(without
(perfect
Kerner
(S17 - S20)
(S57-S60)
(S77 - S80)
adhesion)
adhesion)
φ
f
LewisNielsen
10
0.08
1.14
1.21
1.12
1.08
1.20
1.19
1.07
20
0.15
1.20
1.22
1.21
1.15
1.38
1.39
1.14
30
0.20
1.26
1.27
1.29
1.20
1.50
1.56
1.18
40
0.25
1.35
1.39
1.34
1.25
1.63
1.74
1.23
Table 3.17: Comparison between the predicted and the experimental of relative
modulus of filled acrylic-impact modified composites at 9 phr of acrylic
EFB-Filled Acrylic-Impact Modified Composites
EFB
(phr)
φ
f
10
Experimental Values
Predicted Values
Untreated
(S21 - S24)
Prosil
9234
(S61 - S64)
NZ44
(S81 - S84)
Einstein
(without
adhesion)
Einstein
(perfect
adhesion)
Kerner
LewisNielsen
0.08
1.08
1.16
1.11
1.08
1.20
1.19
1.07
20
0.14
1.21
1.32
1.17
1.14
1.35
1.36
1.13
30
0.20
1.23
1.34
1.27
1.20
1.50
1.56
1.18
40
0.25
1.31
1.40
1.38
1.25
1.63
1.74
1.23
133
Table 3.18: Comparison between the predicted and the experimental relative flexural
modulus of filled acrylic-impact modified composites at 12 phr of acrylic
EFB-Filled Acrylic-Impact Modified PVC-U Composites
Experimental Values
Prosil
Untreated
NZ44
9234
(S25 -S28)
(S85 - S88)
(S65 - S68)
Predicted Values
Einstein
Kerner
(perfect
adhesion)
EFB
(phr)
φ
f
10
0.07
1.05
1.16
1.10
1.07
1.18
1.17
1.06
20
0.14
1.16
1.27
1.21
1.14
1.35
1.36
1.13
30
0.19
1.24
1.31
1.30
1.19
1.48
1.52
1.17
40
0.24
1.33
1.42
1.35
1.24
1.60
1.70
1.22
Einstein
(without
adhesion)
LewisNielsen
A few assumptions have been made in order to apply the predictive models.
Assumptions such as perfect adhesion, spherical shape of EFB, well-dispersed and
random packing have used for Lewis-Nielsen model (Equation 2.6). The maximum
packing volume fraction of filler, φm used was 0.64 (for random packing), which was
suggested by Lewis-Nielsen to calculate ψ (a reduced concentration term) in their
studies. The Poisson’s ratio of PVC was assumed 0.39 (Fried, 2003) and it was
substituted in Kerner’s model (Equation 2.5) to calculate the value of relative
modulus of composites whereas in the Lewis-Nielsen’s model this Poisson’s ratio was
used to calculate the value of A (Einstein coefficient). The value of B (relative shear
modulus of filler and polymer) in Lewis-Nielsen’s model was calculated by assuming
that the modulus of EFB was 9000 MPa, which was also used by Sreekala and
Thomas (2003) in their studies. In this study, the value of A and B obtained by
calculation was 1.23 and 0.413, respectively.
Based on the Equation 3.10, the volume fraction of filler in the composites for
each formulation in this study was calculated.
Mρ
φ = f f
f Mρ
c c
(3.10)
where Mf and Mc are mass of EFB filler and composite in the formulation,
respectively. The volume fraction of filler, φf is a volume occupied by filler in the
134
composites, which varies with EFB filler content and impact modifier content in the
formulation.
Experimental values for untreated composites in Tables 3.14-3.18 were in
good agreement with predicted values of the Einstein model without adhesion. For
treated composites, experimental values were in between predicted values of the
Einstein’s model without adhesion and predicted values of Einstein with perfect
adhesion and with Kerner’s model. These results indicate that the interaction between
fillers and matrix of treated composites has been improved marginally by the addition
of Prosil 9234 and NZ 44. Because the experimental values of relative modulus of
composites treated with Prosil 9234 higher than composites treated with NZ 44, it
proves that Prosil 9234 has a good ability than NZ 44 to enhance the flexural modulus
of composites.
Tables 3.14-3.18 also show that predicted values of the Lewis-Nielsen’s model
which is modified from Kerner’s model and applicable for lower aspect ratio
exhibited slightly lower than experimental values of untreated composites. This is
because the value of B was calculated based on the EFB modulus obtained from the
literature (Sreekala and Thomas, 2003), and not from the experimental work. This
means that the EFB modulus used to calculate B might not represent the actual value
of EFB modulus in this study. In actual case, there is a larger variation of EFB
modulus due to the non-uniformity of the fibres geometry (Sreekala and Thomas,
2003).
D.
FTIR Spectra of Untreated and Treated EFB-Filled PVC-U Composites
A typical FTIR spectrum of PVC-U compound (Figure 3.45) shows two
characteristics bands; a very broad one at 617 and 687 cm-1, probably due to C-Cl
stretching, and a sharp band at 1425 cm-1 due to C-H groups (Yagoubi et al., 1994).
Some oxygenated structures were also detected in the PVC chain or/and in the
135
additives chain, as evidenced by the absorption band at 1727 cm-1, which corresponds
to the carbonyl (C=O) groups (Matuana et al., 2001).
The FTIR spectra of untreated EFB-filled composite (S11) (Figure 3.45b)
showed the increase in the absorption band intensity at 1727 cm-1. Besides that, two
new bands were also observed at 1597 cm-1 and 1163 cm-1. All these bands are
characteristic of the main components of wood (EFB filler). The presence of cellulose
was obvious from the intense and sharp band appearing at 1727 cm-1. This band was
due to the stretching vibration of carbonyl groups (C=O). This stretching might also
come from carbonyl (C=O) linkage in acetyl ester groups in hemicelluloses, aldehyde
in lignin, extractives, and PVC’s additives (Matuana et al., 2001). The two absorption
bands at 1597 cm-1 and 1425 cm-1 of untreated composite (S11) were indicative of the
presence of lignin, an aromatic compound, and attributed to the C=C vibrations of the
benzene ring. The absorption bands at 1163 cm-1 and 1045 cm-1 were assigned to the
ether linkages (C-O-C) from lignin or hemicellulose.
Figure 3.45
FTIR spectra of (a) PVC-U compound (S0) (b) composite (S11)
136
The FTIR spectra of untreated and treated EFB-filled PVC-U composites are
shown in Figure 3.46. The untreated composite (S11), Prosil 9234-treated composite
(S51), and NZ 44-treated composite (S71) samples were used in this analysis. The
absorption band regions at 3200-3600 cm-1 of untreated and treated composites were
probably due to absorption vibration of hydroxyl groups (-OH) and of secondary
amine groups (N-H). The FTIR spectra band of S51 (Figure 3.46) at 1045 cm-1 was
more intense compared to S11 (Figure 3.46) and it may be assigned to the Si-O
stretching vibration. The presence of this functional group was supported by the bands
at 3418 cm-1, and 772 cm-1- 835 cm-1, due to the OH stretching and OH bending
vibration, respectively, from the functional group of Si-OH.. The stretching vibration
of aryl alkyl ether or ether linkage (C-O-C) was also found not to differ greatly from
that of the Si-O system. Similar to Si-O, the absorption band at 1045 cm-1 was
assigned to the C-O-C symmetric stretching vibration from the filler. This band was
supported by C-O-C asymmetric stretching at 1247 cm-1 (Sarani et al., 2001). The
presence of these bands indicated that the Prosil 9234 coupling agent probably
interacted with EFB fillers.
NZ 44 coupling agent also interacted with EFB fillers due to the similarity of
its FTIR spectra (Figure 3.46) with that of S51. The Si-O and Si-OH functional groups
of S51 might be replaced and assigned to the Zr-O and Zr-OH. The formation of ether
linkage also found in this composite. The new bands at 1513 cm-1 and 798-850 cm-1
also emerged on the both spectra of treated composites. The new band at 1513 cm-1
was probably due to NH (amine) symmetric bending which suggested the formation
of amine salt (Matuana et al., 1997) while band at 798-850 cm-1 was due to N-H out
of plane bending. These bands were also supported by the secondary amine groups
(N-H) stretching vibration, which observed at band 3418 cm-1. There is a possibility
that the amino groups, particularly from NZ 44 reacted with PVC. This has also been
reported by Matuana et al. (1997).
137
Figure 3.46
FTIR spectra of (a) filled composite (S11) (b) Prosil 9234-treated filled
composite (S51) (c) NZ 44-treated filled PVC-U composite (S71)
3.3.2.4 Effect of Accelerated Weathering on the Impact and Flexural Properties
This part of study was carried out to observe the effect of accelerated
weathering on the impact strength and flexural properties of PVC-U compound (S0),
impact modified PVC-U compound (S1-S8), EFB-filled PVC-U composites (S9-S12)
and EFB-filled impact modified PVC-U composites (S21-S24 and S37-S40). The impact
modifier content was varied from 3 to 12 phr for S1 to S8 and was fixed at 9 phr for
S21-S24 and S37-S40. The EFB filler content was varied from 10 to 40 phr for all
samples, except samples S1-S8. All samples were weathered for 504 hours.
138
A.
Impact Strength
Figure 3.47 shows the impact strength of PVC-U compound (S0), acrylicimpact modified (S1-S4) and CPE-impact modified (S5-S8) compounds insignificantly
decreased after being exposed to the accelerated weathering. This is due to the values
of impact strength of weathered samples fell within the experimental errors.
Unweathered CPE-impact modified
compounds (S0 and S5- S8)
180.0
Impact strength (kJ/m2)
160.0
Weathered acrylic-impact modified compounds
140.0
120.0
100.0
Unweathered acrylic-impact modified
compounds (S0 and S1-S4)
80.0
60.0
Weathered CPEimpact modified
40.0
20.0
0.0
0
3
6
9
12
Impact modifier content (phr)
Figure 3.47
Impact strength of unweathered and weathered impact modified
compounds
Although the impact strength decreased insignificantly, Table 3.19 shows that
the impact strength of CPE-impact modified compounds greatly decreased compared
to that of acrylic-impact modified compounds due to the effect of photo-oxidation
degradation, which was initiated by UV irradiation in the presence of oxygen and/or
water (Gardiner et al., 1997). The possible reason is the amount of labile chlorine
atom, which releases from the molecular chains during photo-oxidation degradations,
was increased in these compounds. Consequently, the number of active site for
139
propagation reaction of degradation increased (Figure 3.49). The decrease in impact
strength was only marginal for acrylic-impact modified compounds (S1-S4). This is
due to the acrylic was able to tolerate the devastating effects of accelerated
weathering and therefore these compounds were hardly susceptible to the effects. The
excellent weathering performance of acrylic-impact modified compound compared to
CPE has also been reported by Robinovic (1983).
Table 3.19 : Impact strength reduction for impact-modified compounds after
accelerated weathering for 504 hours
Impact modifier content
(phr)
0
Impact strength reduction (%)
Acrylic-impact modified
CPE-impact modified
compounds
compounds
3
3
3
14
25
6
2
59
9
-1
17
12
-1
6
Notation: negative sign (-) shows the value of weathered samples was higher than
unweathered.
Figure 3.48 also shows the decrease in impact strength of EFB-filled
composites (S9-S12) after 504 hours exposure to the accelerated weathering. The effect
of photo-oxidative degradation process, which was initiated by UV irradiation in the
presence of oxygen and moisture in the amorphous regions of PVC, was the main
cause for the decrease in impact strength of weathered filled composites (Gardiner et
al.,1997). The rate of permeability of oxygen and moisture is greater in amorphous
region because the molecular packing is less dense that the degradation process is able
to take place. Some photo-oxidation processes lead to scission of the polymer chain,
while others to intermolecular crosslinking. Intermolecular crosslinking defined as the
joining of two chains or more, (Sarmoria and Enrique, 2004) causes material
embrittlement (Gardiner et al., 1997). Most researchers agreed that crosslinking and
chain scission contribute to the deterioration of the impact strength and other
mechanical properties (Raghi et al., 2000; Matuana et al., 2001; Leong et al., 2003).
140
Unweathered EFB-filled composites
(S9-S12)
9.0
Impact strength (kJ/m2)
8.0
7.0
6.0
5.0
Weathered EFB-filled composites
4.0
3.0
2.0
1.0
0.0
0
10
20
30
40
Filler content (phr)
Figure 3.48
Impact strength of unweathered and weathered EFB filled composites
The suggested reaction scheme for photo-oxidative degradation (similar to
photo degradation) is shown in Figure 3.49 (Matuana et al., 2002; Owen, 1989;
Torikai and Hirose, 1999). The action of UV radiation on PVC produces the singletexcited state of polyene sequence (Figure 3.49), which resulted from the absorption of
conjugated double bonds and carbonyl groups. The most likely bond to be broken in
the excited singlet polyene sequence is the allylic C-Cl linkage, due to its low
dissociation energy. This result in the chlorine radical being released from the excited
singlet polyene sequence and produces a polyenyl radical. The radical then reacts with
the oxygen to produce peroxy radicals on the chain and leads to chain scission
(degradation) or/ and crosslinking of PVC molecular chains.
141
Cl
CH 2 CH CH=CH CH
2
n
hv
Cl
CH 2 CH CH=CH CH
2
n
*
CH 2 C
H
CH=CH
n
CH 2
+
Cl
+ O2
O
O
H2C
H
and/or
Two in chain radicals may recombine to form
crosslink chain
*
CH 2 C
H
CH=CH
+
n
CH 2
*
*
CH 2 CH CH=CH
O
C
*
C
O
n
CH 2
CH 2 C CH=CH CH
2
n
H
H
CH 2 C
CH=CH
CH 2 C
CH=CH
CH=CH n CH 2
Chain Scission
n
n
CH 2
CH 2
H
Crosslinking
Figure 3.49 Suggested reaction scheme for the accelerated photo-oxidation
degradation
The lignin of the incorporated EFB filler primarily broke down under UV
irradiation leading to the generation of the chromophoric functional groups
(impurities) such as carbonyl and hydroperoxy radicals, which accelerated the
degradation of PVC. The increase in the intensity of the C=O stretching bands at
around 1735- 1731 cm-1 as shown in FTIR spectra (Figure 3.59 in part D) provided
good evidence of the incorporation of carbonyl groups into the PVC-U matrix during
processing. The presence of these groups explained the pronounced degradation
observed in the filled composites as compared to unfilled composites (Matuana et al.,
2001). As a result, the brittleness of the filled composites was increased. Table 3.20
shows that the brittleness of the filled composites increased as the filler content
increased.
142
Table 3.20: Percentage of impact strength reduction for filled impact-modified
composites after weathered for 504 hours
EFB filler
content
(phr)
0
EFB-filled
composites
3
10
4
1
13
20
4
2
4
30
6
2
15
40
6
3
9
Impact strength reduction (%)
EFB-filled acrylic-impact EFB-filled CPE-impact
modified compounds
modified compounds
-1
17
Notation: Negative sign (-) shows the value of weathered samples was higher than
unweathered.
Figure 3.50 shows that the addition of 9 phr of acrylic or CPE into EFB filled
PVC-U composites decreased the impact strength of weathered filled impact-modified
composites. The reduction in impact strength of filled CPE-impact modified
composites (S37-S40) was greater than filled acrylic-impact modified composites (S21S24). Similar to the performance of acrylic-impact modified PVC-U compound (S1-S4)
in Figure 3.38, the results in Figure 3.50 and Table 3.20 indicated that the filled
composites added with acrylic were also more stable upon photo-oxidation than filled
CPE-impact modified composites because they were less susceptible UV irradiation.
The reduction of impact strength of filled CPE-impact modified composites in Table
3.20 obviously shows that the combination EFB filler with CPE increased the
propagation reaction of photo-oxidation degradation in the weathered composites. The
synergistic combination of chlorine radicals from PVC and CPE with carbonyl,
hydroperoxy and other radicals from fillers might attribute to the greater reduction in
impact strength of filled CPE-impact modified composites.
143
12.0
Unweathered EFB-filled acrylic-impact
modified composites (S21- S24)
Impact strength (kJ/m2)
11.0
10.0
Unweathered EFB-filled CPE-impact
modified composites (S37- S40)
Weathered EFB-Filled
acrylic-impact modified
composites
9.0
8.0
Weathered EFB-filled CPE-impact
modified composites
7.0
6.0
5.0
0
10
20
30
40
Filler content (phr)
Figure 3.50
Impact strength of unweathered and weathered EFB-filled impact
modified PVC-U composites
B.
Flexural Properties
Similar to impact strength, the reduction in flexural modulus of acrylic-impact
modified compounds (S1-S4) (Figure 3.51), CPE-impact modified compounds (S5-S8)
(Figure 3.51), EFB-filled composites (S9-S12)(Figure 3.53), filled acrylic-impact
modified composites (S21-S24) (Figure 3.56) and filled CPE-impact modified
composites (S37 to S40) (Figure 3.56) were also observed. The reasons for the
reduction of flexural modulus are similar to the reasons as discussed on the reduction
of impact strength. However, some of weathered samples of CPE-impact modified
compounds at 3 phr to 9 phr CPE (Figure 3.51 and Table 3.21) and filled CPE-impact
modified composites at 10phr EFB filler (Figure 3.55 and Table 3.22) slightly
increased in the flexural modulus. The results indicate that samples containing CPE
might be more susceptible to UV irradiation, which resulted in PVC molecular chains
undergoing crosslinking process during photo-oxidation degradation. The influence of
144
crosslinked chains in samples might cause a slight increase in flexural modulus
(Leong et al., 2003).
The flexural strength for all weathered samples is shown in Figures 3.52, 3.54,
and 3.56. Unlike impact strength and flexural modulus, the flexural strength of
weathered samples was higher than that of unweathered samples. The increment of
flexural strength of weathered samples is shown in Tables 3.21 and 3.22. The
compounds and filled composites containing CPE impact modifier exhibited higher
series of values in the increment of flexural strength after 504 hours exposure in
accelerated weathering. These results show that CPE probably has an ability to
accelerate the crosslinking of PVC molecular chains to occur predominantly during
photo-oxidation degradation due to the increase of chlorine atom concentration in the
samples.
The enhancement in the properties of weathered samples is similar with the
findings of other researchers (Radghi et al., 2000) who reported that the tensile
strength of PVC/lignin blend increased after undergoing 129 hours and 480 hours of
accelerated weathering. Similar to the increase of flexural modulus of some weathered
samples as discussed earlier, the increase of flexural strength might be caused by the
crosslinked chains in weathered samples. However, this evidence was not conclusive
because of the fluctuation and small magnitude of increase in the flexural strength and
flexural modulus as well, which fell within the experimental error. Furthermore, other
factors such as filler agglomerations and filler-matrix interaction bonding as
mentioned earlier in Section 3.3.2.2 also influenced the flexural properties results.
145
Unweathered acrylic-impact modified compounds (S1 -S4)
3600
Flexural modulus (MPa)
3400
Unweathered CPE-impact modified
compounds (S5 - S8)
3200
3000
2800
Weathered acrylic-impact
modified compounds
2600
Weathered CPE-impact modified
compounds
2400
2200
2000
6
3
0
9
12
Impact modifier content (phr)
Figure 3.51
Flexural modulus of unweathered and weathered impact compounds
Weathered acrylic-impact modified
Weathered CPE-impact modified
compounds
compounds
Flexural strength (MPa)
100
80
60
Unweathered acrylic-impact modified
compounds (S1-S4)
40
Unweathered CPE-impact modified
compounds (S5 - S8)
20
0
0
3
6
9
Impact modifier content (phr)
Figure 3.52
compounds
Flexural strength of unweathered and weathered impact modified
12
146
Table 3.21: Percentage of flexural modulus reduction and percentage of flexural
strength increment of the impact-modified compounds after 504 hours exposure to
accelerated weathering
Impact
modifier
content
(phr)
0
Flexural modulus reduction (%)
Acrylic-impact
CPE-impact
modified
modified
compounds
compounds
13
13
Flexural strength increment (%)
Acrylic-impact
CPE-impact
modified
modified
compounds
compounds
13
13
3
7
0
4
18
6
5
-2
10
22
9
1
-1
7
13
12
3
7
8
0
Notation: Negative sign (-) shows the value of weathered samples was higher than
unweathered.
Table 3.22: Percentage of flexural modulus reduction and percentage of flexural
strength increment of the filled composites and filled impact-modified composites
after 504 hours exposure to accelerated weathering.
EFB
filler
content
(phr)
0
Flexural modulus reduction (%)
EFB-filled
EFB-filled
CPEacrylicEFB-filled
impact
impact
composites
modified
modified
composites composites
13
2
-1
Flexural strength increment (%)
EFB-filled
EFB-filled
CPEacrylicEFBimpact
impact
filled
modified
modified
composites
composites composites
13
7
13
10
9
4
-2
4
13
16
20
10
10
3
0
5
10
30
0
10
11
11
2
7
40
15
8
23
0
4
15
Notation: Negative sign (-) shows the value of weathered samples was higher than
unweathered.
147
Flexural modulus (MPa)
5000
Unweathered EFB-filled composites (S9 -S12)
4000
3000
2000
Weathered EFB-filled composites
1000
0
0
Figure 3.53
10
20
Filler content (phr)
30
40
Flexural modulus of unweathered and weathered EFB-filled PVC-U
composites
Flexural strength (MPa)
100.0
Weathered EFB-filled composites
80.0
60.0
Unweathered EFB-filled composites (S9- S12)
40.0
20.0
0.0
0
Figure 3.54
composites
10
20
Filler content (phr)
30
Flexural strength of unweathered and weathered EFB-filled PVC-U
40
148
Flexural modulus (MPa)
4000
Unweathered EFB-filled acrylicimpact modified composites (S21- S24)
3500
Unweathered EFB-filled CPE-impact
modified composites (S37- S40)
3000
2500
Weathered EFB-Filled CPEimpact modified composites
Weathered EFB-filled acrylicimpact modified composites.
2000
1500
0
10
20
30
40
Filler content (phr)
Flexural modulus of unweathered and weathered EFB-filled impact
Figure 3.55
modified composites
Weathered EFB-filled acrylic-impact
modified composites
Flexural strength (MPa)
80.0
70.0
Weathered EFB-filled CPEimpact modified composites
60.0
Unweathered EFB-filled acrylic
impact modified composites (S21-S24)
50.0
Unweathered EFB-filled CPE-impact
modified composites (S37-S40)
40.0
30.0
0
10
20
30
40
Filler content (phr)
Figure 3.56
Flexural strength of unweathered and weathered EFB-filled impact
modified composites
149
C.
Visual Inspection
The effect of accelerated weathering on the appearance of all the samples
surfaces was also studied by visual inspection of the exposed sides of samples (Figure
3.57). Samples of PVC-U compound (S0) and impact modified PVC-U compounds
(S1-S4 and S5-S8) suffered discolouration (from white to yellowish). This was due to
the presence of chromophoric groups, particularly carbonyl functional groups, which
formed on PVC under the effect of the UV irradiation. Meanwhile, for unmodified
and impact modified filled composites (S9-S12, S21-S24 and S37-S40), the initial colour
was dark brown, which later changed to light brown after exposure to UV irradiation.
In terms of discolouration level, the composites samples exhibited greater
discolouration than that of unfilled samples. This showed that the addition of carbonyl
functional groups contributed by EFB fillers within the PVC-U matrix caused the
discolouration process to take place aggressively. The discolouration also provided
an additional evidence of photo-oxidation of the samples. No cracks have been
noticed after this period of weathering for all samples.
Figure 3.57
Appearance of some samples surface before and after exposed to UV
irradiation for 504 hours
150
D.
FTIR Spectra
The FTIR spectroscopy has been used to study changes in the surface
chemistry of polymer after weathering (Matuana et al., 2001; Stark and Matuana,
2004). FTIR spectroscopy was used as a complementary technique to monitor
functional groups of weathered compounds and composites samples. The FTIR
spectra of unweathered and weathered samples for PVC-U compound (S0), acrylicimpact modified compound (S3), CPE-impact modified compound (S7) and EFB-filled
composite (S11) are shown in Figures 3.58-3.61, respectively.
It can be seen that the formation of conjugated carbonyl groups (C=O
stretching) was easily recognized at 1735 cm-1 for weathered PVC-U sample (Figure
3.58). This absorption band (intensity) may be assigned to functional groups
containing carbon-carbon double bonds (R2-C=C) conjugated to carbonyl groups
(Matuana et al., 2001). Similar to the weathered PVC-U compound, the absorption
bands at 1735 cm-1 of weathered composite (Figure 3.59), acrylic-impact modified
(Figure 3.60) and CPE-impact modified sample (Figure 3.61) were also due to
carbonyl groups. Although the carbonyl groups absorption band also emerged at 1735
cm-1 for unweathered composite and unweathered impact-modified samples but the
peak of this band was blunted. The photo-oxidation degradation was also reflected by
the formation of unsaturated vinyl groups (RCH=CH2) in the absorption of 1653-1648
cm-1 (C=C stretching) in the FTIR spectra of weathered samples as shown in Figures
3.58-3.61 (Matuana et al., 2001; Wan et al., 2004).
The vinyl group formation was also supported by the new region of 970 cm-1
for all weathered samples (Stark and Matuana, 2004). Based on this peak, similar to
the carbonyl formation, the increase in vinyl group concentrations suggested that the
chain scission took place not only at the polymer chains but also at the EFB filler.
Furthermore, the absorption bands at the regions of 1430 cm-1 in the FTIR spectra of
weathered samples, which were associated with =C-H out of plan bending were also
151
indicative of photo degradation of samples upon exposure to UV irradiation (Pavia et
al., 1979).
(b)
Figure 3.58
compounds
FTIR spectra of (a) unweathered and (b) weathered PVC-U
152
(a)
(b)
Figure 3.59
FTIR spectra of (a) unweathered and (b) weathered-EFB-filled
composites
(a)
(b)
Figure 3.60
FTIR spectra of (a) unweathered and (b) weathered-acrylic-impact
modified composites
153
(a)
(b)
Figure 3.61
FTIR spectra of (a) unweathered and (b) weathered-CPE-impact
modified composites
3.3.2.5 Effect of NPCC on the Impact Strength and Flexural Properties
The study was conducted to observe the possibility of using NPCC as impact
modifier for the EFB-filled PVC-U composites. A preliminary study on the effect of
NPCC on the PVC-U compound was first carried out.
A.
Impact Strength
Figure 3.62 illustrates that the impact strength has significantly enhanced upon
the addition of 10 phr NPCC. No further increase was observed with further
incorporation of NPCC fillers. Recall from Section 3.3.2.1 (B), that the incorporation
of EFB fillers decreased the impact strength of the composites. This preliminary result
154
indicates that NPCC has the potential to be used as an impact modifier in the PVC.
The ability of nano calcium carbonate (NCC) in enhancing the impact strength of the
composites has also been reported by Chen et al.(2004). They found that the impact
strength of PVC/NCC compound was significantly enhanced after the incorporation
of 10 phr NCC.
16.0
NPCC-filled composites (S89-S91)
Impact strength (kJ/m2)
14.0
12.0
10.0
EFB-filled composites (S9-S12)
8.0
6.0
4.0
2.0
0.0
0
Figure 3.62
10
20
30
Filler content (phr)
40
50
Effects of EFB filler and NPCC on the impact strength of composites
The second part of the study the investigation was to observe whether the
NPCC fillers can also significantly enhance the impact strength of the composite
when used together with EFB fillers. Besides that, the previous results of impact
strength of EFB-filled composites (S9-S12) and EFB-filled impact modified
composites containing 3 phr acrylic (S13-S16) and 3 phr CPE (S29-S32) were also
replotted in Figure 3.63 in order to compare the ability of NPCC filler with acrylic
and CPE impact modifier in enhancing the impact properties of filled composites.
The results shows that the impact strength of EFB-filled composites
containing 10 phr NPCC (S92-S95) and 20 phr NPCC (S96-S99), respectively, decreased
drastically as the EFB filler contents increased from 10 to 40 phr. Although all the
filled composites show a similar trend on the impact strength with increasing EFB
155
filler contents, the rate of decrease of filled composites incorporated with NPCC
fillers was larger than that of the acrylic and CPE-impact modified filled composites.
The results also show that when hybrid fillers are used, the impact strength was lower
than when only EFB filler was used. The results also revealed that NPCC filler
unable to perform as impact modifier in EFB-filled composites. The inability of stress
to distribute uniformly upon impact and inability of matrix to shear yield before
fracture due to the increase of filler proportion in the matrix are the plausible reasons
for the decreasing in the impact strength of hybrid filled composites (Marthur and
Vanderheiden,1986).
EFB filled composites (S9-S12)
EFB-filled composites added with 3 phr
acrylic (S13-S16)
EFB-filled composites added with 3 phr
CPE (S29-S32)
EFB filled composites added with 10 phr
NPCC (S92-S95)
EFB-filled composites added with 20 phr
NPCC (S96-S99)
Impact strength (kJ/m2)
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
0
10
20
30
40
50
EFB filler content (phr)
Figure 3.63
Effects of 10 phr NPCC, 20 phr NPCC, 3 phr acrylic and 3 phr CPE on
the impact strength of EFB-filled composites
156
B.
Flexural Properties
Figure 3.64 shows the effect of NPCC filler on the flexural modulus of filled
composites. The result on the effect of EFB filler (from Section 3.3.2.2 B) is also
replotted as a comparison. The results revealed that EFB filler was more effective in
increasing the stiffness of composites at all filler contents. The ability of NPCC and
EFB fillers to restrict the mobility of PVC molecular chains by reducing the free
volume of the PVC molecules may be attributed to the increasing filled composites
stiffness. However, the result revealed that EFB was more effective in increasing the
stiffness of composites compared to NPCC at all filler contents. The lower aspect
ratio of NPCC could not restrict effectively the mobility of PVC molecular chains.
Similar to flexural modulus, the flexural strength of NPCC-filled composites was
lower than EFB-filled composites as shown in Figure 3.65. The inability to support
stresses transferred from the matrix due to the lower aspect ratio is a reason for the
Flexural modulus (MPa)
decreasing in flexural strength of NPCC-filled composites.
5000
4500
4000
3500
EFB-filled composites (S9-S12)
3000
2500
2000
1500
1000
NPCC-filled composites (S89-S91)
500
0
0
10
20
30
40
50
Filler content (phr)
Figure 3.64
composites
Effects of EFB (S9-S12) and NPCC (S89-S91) on the flexural modulus of
Flexural strength (MPa)
157
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
EFB-filled composites (S9-S12)
NPCC-filled composites (S89-S91)
0
10
20
30
40
50
Filler content (phr)
Figure 3.65
Effects of EFB (S9-S12) and NPCC (S89-S91) on the flexural modulus of
composites
Figure 3.66 depicts that the EFB-filled composites containing 20 phr NPCC
(S96-S99) has the greatest stiffness compared to other filled composites. The flexural
modulus of the composites with 20 phr NPCC was significantly higher than the EFBfilled composites with only 10 phr NPCC (S92-S95). The increase of filler proportion
in the composites is attributed to the increase of flexural modulus. The results also
show that the filled impact modified composites (S13-S16 and S29-S32) samples have
lower stiffness compared to the EFB-filled composites containing 10 phr NPCC. The
softening effect generated by 3 phr acrylic (S13-S16) and 3 phr CPE (S29-S32) is a cause
for the lower stiffness of the filled impact modified composites.
Figure 3.67 shows that the flexural strength of EFB-filled composites
containing 10 phr or 20 phr NPCC was lower than the EFB-filled composites without
NPCC filler. The increase of detrimental effect due to the increase of filler proportion
in the composites was the main reason. The result shows that the composites
containing 10 phr and 20 phr NPCC had a lower flexural strength compared to other
filled composites. As mentioned earlier, the presence of NPCC with low aspect ratio
158
and incapable of EFB filler to facilitate a better transfer of stress, thus increased the
deleterious effect of filler on the filled composites. Therefore the flexural strength of
EFB-filled composites containing NPCC filler decreased as the EFB filler content
increased from 0 to 40 phr.
EFB-filled composites (S9-S12)
EFB-filled composites added with 3 phr acrylic (S13-S16)
EFB-filled composites added with 3 phr CPE (S29-S32)
EFB-filled composites added with 10 phr (S92-S95)
EFB-filled composites added with 20 phr NPCC (S96-S99)
5000
Flexural modulus (MPa)
4500
4000
3500
3000
2500
0
10
20
30
40
50
EFB filler content (phr)
Figure 3.66
Effects of 10 phr NPCC, 20 phr NPCC, 3 phr acrylic and 3 phr CPE on
the flexural modulus of the EFB-filled composites
159
EFB-filled composites (S9-S12)
EFB-filled composites added with 3 phr acrylic (S13-S16)
EFB-filled composites added with 3 phr CPE (S29-S32)
EFB-filled composites added with 10 phr NPCC (S92-S95)
EFB-filled composites added with 20 phr NPCC (S96-S99)
Flexural strength (MPa)
90.0
85.0
80.0
75.0
70.0
65.0
60.0
55.0
50.0
0
10
20
30
40
50
EFB filler content (phr)
Figure 3.67
Effects of 10 phr NPCC, 20 phr NPCC, 3 phr acrylic and 3 phr CPE on
the flexural strength of the EFB-filled composites
3.3.2.6 Effect of Extracted EFB filler on the Impact Strength and Flexural
Properties
This study was carried out in order to observe the effect of residues oil in the
EFB fillers on the mechanical properties of composites. Comparison will be done to
observe whether the extracted EFB filler has a better ability than the unextracted EFB
filler in enhancing the mechanical properties of composites. Therefore, the previous
mechanical properties of filled composite containing 30 phr unextracted EFB filler
was also used as comparison.
160
A.
Impact Strength
Figure 3.68 shows the effect of extracted fibre on the impact strength of filled
composites. It shows that the impact strength of the composite filled with 30 phr
extracted filler is marginally higher than the composites with unextracted filler. The
degree of enhancement is only about 0.3 %. This indicates that the amount of the oil
present in the EFB filler is not a significant factor to influence the impact strength of
the filled PVC-U composites. The impact strength of oil extraction filler in the present
study is less significant compared to previous study on polypropylene composite
(Rozman et al., 2001), which may be due to the polarity of PVC molecules, which
enable the polymer to have a good interaction even with oil residue present in the
fillers.
8.00
30 phr
Impact strength (kJ/m2)
6.11
6.13
6.00
4.00
2.00
0.00
Unextracted-filled
composite (S11)
Figure 3.68
Extracted-filled
composite (S47)
Effect of unextracted and extracted EFB filler on the impact strength
of composites at filler content of 30 phr
161
B.
Flexural Properties
Figure 3.69 shows that the flexural modulus of extracted-filled composite is
slightly lower compared to unextracted filler.
The plausible reason is that the
extraction does not only remove the residues of oil but also other extractives in the
fillers. Thus, it causes the extracted filler to decrease in compaction and to have many
cavities on the surface (Figure 5.10). The decrease of extracted filler rigidity caused a
slight decrease in the flexural modulus of the filled composite. Figure 3.70 depicts the
results of flexural strength of filled composites. The result shows that there is no
significant improvement (only about 3 %) in flexural strength of the composite filled
with 30 phr extracted filler compared to the unextracted filler. The relatively similar
result in the interaction of extracted or unextracted filler with the matrix is a plausible
reason to the insignificant changed in the flexural strength.
4400
30 phr
4300
Flexural modulus(MPa)
4200
4142
4100
4000
3900
3900
3800
3700
3600
3500
3400
Unextracted-filled
composites (S11)
Figure 3.69
Extracted-filed
composites (S47)
Effect of unextracted and extracted EFB filler on the flexural modulus
of composites at filler content of 30 phr
162
80.0
30 phr
Flexural strength (MPa)
78.0
76.0
74.5
74.0
72.4
72.0
70.0
68.0
66.0
64.0
Unextracted-filled
composites (S11)
Figure 3.70
Extracted-filled
composites (S47)
Effect of unextracted and extracted EFB filler on the flexural strength
of composites at filler content of 30 phr
3.3.2.7 Water Absorption
In this study, the effect of acrylic, CPE, untreated and coupling agent-treated
filler content on the water absorption of filled composites was investigated. The
results in Figure 3.71 and Table 3.23 show that the incorporation of impact modifier
increased the percentage of water absorption PVC for 60 immersion days. The water
absorption increased with increasing impact modifier content. The increase in the
polarity, which was generated by the presence CPE and acrylic in compounds is the
main reason for the increasing of water absorption. The polarity of molecular chains
of CPE and acrylic is due to chlorine atoms and oxygen atom, respectively. Table
3.23 also shows that acrylic-impact modified compounds has a slight higher values of
water absorption compared to CPE-impact modified compounds.
163
0.4
12 phr CPE (S8)
Water absorption (%)
0.3
12 phr acrylic (S4)
9 phr acrylic (S3)
6 phr acrylic (S2)
9 phr CPE (S7)
6 phr CPE (S6)
0.2
3 phr acrylic (S1)
3 phr CPE (S5)
0.1
PVC-U (S0)
0.0
0
10
20
30
40
50
60
70
Immersion Day
Figure 3.71
Effects of impact modifier content on water absorption of acrylic-
impact modified (S1-S4) and CPE-impact modified compounds (S5-S8)
Table 3.23: Percentage of water absorption of impact modified compounds and EFB-
filled composites
Impact
modifier
content
(phr)
Water absorption
of Impact-modified
compounds(%)
0
Acrylic
0.10
CPE
0.10
3
0.16
6
EFB
filler
content
(phr)
Water absorption
of EFB-filled composites (%)
0
Untreated
0.10
Prosil 9234
0.10
NZ44
0.10
0.13
10
0.74
0.60
0.72
0.22
0.18
20
1.69
1.33
1.53
9
0.23
0.21
30
2.89
2.21
2.32
12
0.27
0.30
40
4.08
3.95
3.84
164
In order to compare the effect of filler on the absorption clearly, only the
results of unmodified and modified composites filled with 20 phr and 40 phr were
plotted. The result given in Figure 3.72 shows that the water absorption of unmodified
and impact modified composites was significantly increased as the filler content
increased. This was expected due to the hydrophilic nature of the cellulosic filler. The
polar hydroxyl groups in their molecular structures are able to form hydrogen bonds
with water molecules. The higher the proportion of EFB filler in the composites, the
higher possibility of water is being absorbed through the formation of hydrogen
bonds. Thus, the water absorption increased proportionally with the filler content, as
shown in Table 3.23. Similar observations have been reported by other researchers
who used EFB filler in different polymer matrices (Rozman et al., 2000; Abdul Khalil
et al., 2000). Figure 3.72 shows that the water absorption of impact-modified
composites was higher than unmodified composites. Similar to the impact modified
compounds, the increase in polarity, which was contributed by impact modifier, is the
main cause for the higher water absorption of impact-modified composites.
5.0
40 phr EFB,9 phr acrylic (S24)
4.5
40 phr EFB,9 phr CPE (S40)
Water absorption(%)
4.0
40 phr EFB (S12)
3.5
3.0
2.5
20 phr EFB,9 phr CPE (S38)
2.0
20 phr EFB,9 phr acrylic (S22)
1.5
20 phr EFB (S10)
1.0
0.5
0.0
0
Figure 3.72
10
20
30
40
Immersion day
50
60
70
Effect of EFB filler content on the water absorption of unmodified and
modified composites
165
Figures 3.73 and 3.74 show the effect of coupling agents on the water
absorption of unmodified and impact-modified composites, respectively. The results
show that Prosil 9234 and NZ44 significantly reduced the water absorption of
composites. The ability of coupling agents to modify the cell wall of filler made the
EFB filler to be less hydrophilic. Coupling agent has an ability to interact with
hydroxyl groups of EFB, thus blocking the latter from hydrogen bonding with water.
It was discovered that unmodified (Table 3.23) and impact-modified composites
(Table 3.24) treated with Prosil 9234 exhibited slightly less hydrophilic than NZ 44 as
filler content increased from 10 to 30 phr. Figure 3.73 also shows that at 40 phr the
water absorption of filler treated with both coupling agents was almost similar.
Meanwhile, Figure 3.74 and Table 3.24 show that at 40 phr the water absorption of
filler treated with Prosil 9234 was slightly higher than untreated. This result shows
that the ability of Prosil 9234 to reduce the hydrophilic of filler was ineffective at
higher filler content (40 phr), due to the domination of filler content. It shows that the
amount of Prosil 9234 used to treat the 40 phr fillers was insufficient to modify the
fillers completely. NZ 44 was able to modify the hydrophilic of fillers at higher filler
content.
4.5
40 phr EFB(S12)
Prosil 9234-40 phr EFB(S52)
Water absorption (%)
4.0
3.5
NZ 44-40 phr EFB(S72)
3.0
2.5
20 phr EFB(S10)
2.0
1.5
NZ 44-20 ph rEFB(S70)
1.0
Prosil 9234-20 phr EFB(S50)
0.5
0.0
0
10
20
30
40
50
60
70
Immersion day
Figure 3.73
Effect of coupling agents on the water absorption of treated
unmodified composites
Water absorption (%)
166
Prosil 9234-40 phr EFB, 9 phr acrylic (S64)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
40 phr EFB, 9 phr acrylic (S24)
NZ 44-40 phr EFB,9 phr acrylic(S84)
20 phr EFB,9 phr acrylic(S22)
NZ 44-20 phr EFB,9 phr acrylic(S82)
Prosil 9234-20 phr EFB,9 phr acrylic(S62)
0
10
20
40
30
60
50
70
Immersion day
Figure 3.74
Effect of coupling agents on the water absorption of treated acrylic-
impact modified composites
Table 3.24: Percentage of water absorption of impact modified compounds and impact
modified treated composites
EFB filler
content
(phr)
0
Water absorption EFB-filled impact modified composites (%)
9 phr CPE
9 phr acrylic
Untreated
Untreated Prosil 9234-treated NZ44-treated
0.21
0.23
0.23
0.23
10
1.03
0.95
0.65
0.76
20
2.08
2.10
1.45
1.66
30
3.15
3.14
2.35
2.54
40
4.46
4.61
4.81
4.14
167
3.4 Conclusions
The main purpose in this study is to determine the impact and the flexural
properties of EFB filled PVC-U composites. The composites were impact modified
with acrylic and CPE, and treated with Prosil 9234 and NZ 44 coupling agents. Based
on the results obtained, the following conclusions can be made:
(a)
The flexural modulus of EFB-filled PVC-U composites increased with EFB
filler contents, whereas the impact and flexural strength decreased. The
increase of filler contents contributed to the increase composites stiffness.
Factors such as filler agglomeration and low aspect ratio of filler and the
weakness of filler-matrix interface contributed to the impact and flexural
strength decrement.
(b)
The addition of acrylic and CPE impact modifier improved the impact strength
of the composite. Impact modifier allowed PVC-U matrix to yield before
fracture. However, the rubbery phase of impact modifier also softened the
composites. As a result, the flexural properties of impact-modified composites
were decreased. CPE has a greater softening effect on the composite than
acrylic impact modifier. The polarity of both impact modifiers increased water
absorption of the composites.
(c)
The Prosil 9234 and NZ 44 improved the impact and flexural properties of the
composites. The coupling agents have ability to improve the filler-matrix
interface of the composite by introducing ether linkage between the filler and
matrix. The FTIR spectra obtained in this study showed that there was
interaction between filler and PVC matrix. The presence of this interaction
was supported by a reduction in water absorption of treated composites. The
coupling agents interacted with hydroxyl groups of EFB, thus blocking the
latter from hydrogen bonding with water The interaction, however,
168
insufficient to bring about better enhancement of composite impact strength
and flexural properties. Therefore, the flexural modulus obtained from
Einstein Model without adhesion in good agreement with the modulus
obtained in this study. In other words, the interaction between treated filler and
PVC was only improved slightly. Prosil 9234 was found more effective than
NZ 44 in improving the mechanical properties of composite.
(d)
The flexural strength of compounds and composites increased after exposed
for 504 hours in the accelerated weathering environment, but the flexural
modulus and impact strength were decreased.
Overall, acrylic impact
modified compounds and EFB-filled acrylic-impact modified composites were
more stable than others. Incorporation of EFB accelerated the photo-oxidation
degradation, particularly for EFB-filled composites containing CPE impact
modifier.
(e)
The impact and flexural strength of composites insignificantly improved but
the flexural modulus decreased marginally when the extracted EFB filler
incorporated in composites. NPCC filler was able to increase the impact
strength but not for flexural properties of composites compared to EFB filler.
The NPCC filler cannot be used as impact modifier in the EFB-filled
composites due to the inability of NPCC to enhance the impact strength of
composites.
CHAPTER 4
THERMAL PROPERTIES OF COMPRESSION MOULDED PVC-U
COMPOSITES
4.1
Introduction
PVC is thermally unstable, especially at elevated temperature, and in presence
of oxygen and humidity. The degradation of PVC has been shown by most researchers
to proceed in two distinct stages (Marcilla and Beltran, 1995; McNeill et al., 1995). The
first stage corresponds to the dehydrochlorination to form polyene with subsequent
formation of conjugated polyene sequences of doubles bonds (-HC=CH-) in the
backbone of the polymer after splitting of the first hydrogen chloride (HCl) molecules
(initiation reaction), accompanied by the formation of small amounts of hydrocarbons,
mainly aromatics such as benzene, napthelene and others. The second stage
corresponds to the scission of the polyene sequences, which formed during the first
stage (Marcilla and Beltran, 1995; Mc Neill et al., 1995). Accordingly, one might
expect that in the thermogravimetric (TG) curve of PVC, the first weight loss would be
due to HCl evolution, while the second, would be due to the evolution of hydrocarbons
(Montaudo and Puglisi, 1991). At the last stage, a black carbonaceous residue known as
char was obtained.
170
Klaric et al. (2000) have studied the thermal stability of PVC blended with
chlorinated polyethylene (CPE) impact modifier. The blend has also produced the two
stages of degradation in which the dehydrochlorination took place in the first step and
followed by the degradation of dehydrochlorinated sequences, in the second step. The
addition of CPE have improved the thermal stability of PVC for all compositions
investigated. The thermal stability of PVC blended with acrylic impact modifier has not
been reported in literature. Pavlinec et al. (1997) have, however, studied the thermal
stability of polymer bead consists of poly (methyl methacrylate) (PMMA) core and
poly (butyl acrylate) (PBAC) copolymer shell. They found that the PBAC, which is an
impact modifier, was more stable than PMMA. The PBAC degradation temperature
was observed to occur at 380-390 oC while PMMA at 340-350 oC.
The effect of impact modifiers on the heat deflection temperature of PVC has
been studied by previous researchers (Deanin and Chuang, 1986; Lutz, 1993). HDT is
often related to the mechanical behaviours of the materials. Deanin and Chuang (1986)
reported that addition of impact modifiers (ABS and CPE) have lower the HDT of rigid
vinyl polymers progressively. It means that impact modifiers were able to reduce the
modulus of rigid vinyl polymers. However, according to Lutz (1993), HDT has
appeared to be more affected by the molecular weight (K-value) of the PVC than by the
impact modifier content.
Pedro et al. (2001) characterized the agalmatolite-filled PVC composites using
a differential scanning calorimetry (DSC). DSC results showed that there were a slight
decrease in the glass transition temperature (Tg) as the agalmatolite filler content
increased from 10 to 40 phr. However, the similar trend was not observed in the
composites filled with calcium carbonate filler, which practically did not show any
difference in Tg, as the filler content increased (Pedro et al., 2001). Meanwhile,
Sombatsompop et al. (2003) has reported that the Tg of PVC increased with increasing
wood sawdust content.
171
Since most polymers are processed at high temperature, thermal stability of
natural fibres is also one of the factors to be considered in developing natural fibrefilled composite. Thermal stability of lignin was considered to be greater than that of
hemicellulose and less than that of cellulose (Beall and Eickner, 1970). Based on
thermogravimetric analysis (TGA) conducted by Thiebaud et al. (1997), they found
that the untreated oak wood started to lose weight at the temperature range of 22-200
o
C due to the evaporation of water in the wood. The significant weight loss occurred at
temperature range of 200-330
o
C, which corresponded to the degradation of
hemicellulose while at temperature range of 330-490 oC corresponded to cellulose.
Nguyen et al. (1981) found that the pyrolisis of hemicelluloses, lignin and cellulose of
wood fibre occurred at 200, 220 and 250 oC, respectively.
In recent years, most studies conducted involved investigating the mechanical
properties of natural fibre-filled polymer composites as a function of fibre loading,
using various treatments for the fibres. Very few workers have investigated the thermal
stability of the EFB-filled PVC-U composites. Therefore, the aim of the study in this
chapter is to investigate the thermal behaviours such as heat deflection temperature,
glass transition temperature, and thermal degradation temperature of the composites.
4.2
Experimental
In this section, the materials, filler preparations, and blend formulation used are
similar to Chapter 3. The HDT, DSC, and TGA analysis carried out in this chapter are
described.
172
4.2.1 Materials, Filler Preparation and Blend Formulations
The blend formulations as summarized in Table 3.3 were selected and used in
this study. The blend formulations used for HDT were PVC-U compound (S0), impactmodified PVC-U (S1-S8), EFB-filled PVC-U composites (S9-S12), and EFB-filled
impact-modified PVC-U composites (S21-S24 and S37-S40). The blend formulations used
for DSC were S0, S3, S7, S9-S12, S21-S24 and S37-S40. For TGA, blend formulation used
were S0, S9 to S12, S21-S24 and S37-S40. The neat PVC resin, EFB filler, acrylic, and CPE
impact modifier were also analysed using TGA.
4.2.2 Sample Preparations
As described in detail in Sections 3.2.4-3.2.6 (Chapter 3), the dry blending of
each formulation was first done using a laboratory high-speed mixer. The dry blended
compounds were then melt-blended and sheeted using a two-roll mill. The milled
sheets were then placed into a mould and hot pressed. The moulded test specimens
were used as samples for thermal analysis.
4.2.3
Heat Deflection Temperature Testing
The heat deflection temperature test was conducted using Toyo-Seiki HDT S-3
tester, following ASTM D 648, with flexural load of 1.2 kg and a heating rate of 2 +
0.2 oC/min. The samples with standard dimensions of 125 x 13 x 3 mm3 were immersed
under flexural load into a heated bath of silicone oil. The temperature of the oil was
measured when the test bar deflected by 0.25 mm. This temperature was recorded as
173
the deflection temperature under flexural load of the test sample. All reported values
for the test were the average of two specimens.
4.2.4 Differential Scanning Calorimetry Study
Differential scanning calorimetry (DSC) was carried out according to ASTM
D3418-82 at a heating rate of 10 0C/min to ensure high resolution of the DSC curve,
and at temperature ranging from 30 to 250 0C. A Mettler Toledo DSC model 821 with
STAR system was used. The liquid nitrogen rate was maintained at 50 ml/min. The
calorimeter was calibrated with an indium reference. Meanwhile, samples in the size
range 4.5-5.5 mg were placed in a sealed aluminium pan and an empty aluminium pan
was used as the reference. The tangent method was used to determine the glass
transition temperature (Tg) of the samples. The mid-point of the first endothermic
baseline in the DSC heating curve was taken as the Tg.
4.2.5 Thermogravimetric Analysis
The thermogravimetric analyser used for the thermal degradation study was a
Perkin Elmer-TGA 7. Approximately 9.5-10.0 mg of samples was scanned from 30 to
800oC, at heating rate of 10 oC /min. Each sample was placed in an open platinum
sample pan. The purge gas used was nitrogen at a flow rate 20 cm3/min. The onset
temperature of a 5% (T5%) weight loss deviation from the baseline of the
thermogravimetric (TG) curve was used as the indicator of the composite’s thermal
stability. The onset temperature for degradation was found to be tremendously
dependent on the run
conditions (Klaric et al.,
2000). The differential
thermogravimetric (DTG) curve for weight loss was also recorded.
174
4.3
Results and Discussion
In this section, results on heat deflection temperature testing, differential
calorimetry study and themogravimetric analysis of the unmodified and impact
modified of composites will be presented.
4.3.1 Heat Deflection Temperature
Table 4.1 shows the effect of impact modifier content on the HDT of the
impact-modified PVC-U. The HDT of the PVC-U compound (S0) obtained was 66 oC.
This value was within the range of HDT of PVC commercial grades reported by Fried
(2003). In general, the decrease of HDT due to the addition of both impact modifiers
was not significant. The decreased in HDT was only marginal as the impact modifier
content increased from 3 to 12 phr. A similar trend has also been reported by Deanin
and Chuang (1986) for the acrylonitrile butadiene styrene (ABS) and CPE impact
modified PVC. Both impact modifiers have slightly decreased the HDT of PVC. The
results shown in this study were also in an agreement with the results obtained by Lutz
(1993), who reported that the HDT was more affected by the molecular weight of PVC
compared to the impact modifier content.
Although the results in Table 4.1 do not show significant difference in HDT as
the impact modifier content increased, the information can be used to distinguish the
softening effect contributed by acrylic and CPE impact modifier. The softening effect
was able to reduce the rigidity of PVC-U compounds by means of reducing the strength
of intermolecular interaction (Deanin and Chuang, 1986). The HDT of acrylic-impact
modified PVC-U (S1-S4) was found slightly higher than CPE (S5-S8). It shows that the
CPE impact modifier had greater softening effect than acrylic for the similar reasons
enumerated in Section 3.3.2.2 (Chapter 3). As a result, the flexural modulus and
175
strength of the CPE-impact modified PVC-U compounds were also lower than acrylicimpact modified PVC-U as the impact modifier content increased.
Table 4.1: HDT of acrylic-impact modified and CPE-impact modified PVC-U
compounds
S0
Acrylic content
(phr)
0
HDT
(oC)
66.0 + 0.3
S1
3
S2
S0
CPE content
(phr)
0
HDT
(oC)
66.0 + 0.3
65.8 + 0.1
S5
3
65.0 + 0.1
6
65.6 + 0.1
S6
6
64.9 + 0.1
S3
9
64.9 + 0.6
S7
9
64.7 + 0.4
S4
12
65.0 + 0.1
S8
12
64.3 + 0.1
Sample
Sample
Tables 4.2 and 4.3 show the HDT for the unmodified filled composites (S9-S10)
and impact-modified filled PVC-U composites (S21-S24 and S37-S40), respectively. The
results showed that the HDT of S0 was slight higher than that of the S9 composites. A
similar result was also found in the work of Chiu and Chiu (1996, 1998), who
investigated the relationship between HDT and carbon black content in copolymer
polypropylene. They found that that the HDT of the blend decreased as the carbon
black content increased. The decrease in HDT upon incorporation of 10phr EFB filler
was probably caused by the fact that the silicone oil was able to penetrate into the
composites and acted as a lubricant, affecting the filler-matrix interface. It was found
that the filled unmodified composites slightly increased in weight by 0.2 % on
immersion in silicone oil for the HDT measurement. The HDT of composites increased
insignificantly with a further increase of fillers from 10 to 40 phr. It has been reported
that the incorporation of fillers into highly crystalline polymers generally contributed to
an increase in HDT (Schwartz, 1987). However, PVC polymer, with only about 5-10 %
crystallinity was incapable of undergoing a significant improvement in HDT as the
filler content increased. The amorphous PVC and the lubrication effect of silicon oil
were attributed to the insignificant improvement in HDT. This is due to the mobility of
PVC chains was less restricted.
176
Similar results (Table 4.3) were also obtained for S21-S24 and S37-S40 where the
HDT was not significantly increased with increasing filler content. The softening effect
produced by the acrylic and CPE was also experienced by the S21-S24 and S37-S40.
Therefore, the HDT of these impact-modified filled composites were slightly lower
than the unmodified filled composites. As mentioned earlier, CPE had a greater
softening effect than acrylic, thus the HDT values of S37-S40 were slightly lower than
S21-S24.
Table 4.2: HDT of EFB-filled PVC-U composites
S0
EFB filler content
(phr)
0
HDT
(oC)
66.0 + 0.3
S9
10
64.7 + 0.1
S10
20
65.1 + 0.6
S11
30
66.3 + 1.6
S12
40
66.0 + 1.0
Sample
Table 4.3: HDT of EFB-filled acrylic-impact modified and EFB-filled CPE-impact
modified PVC-U composites
EFB
HDT
filler
(oC)
content
(phr)
0
64.9 + 0.6
Sample
CPE
content
(phr
S7
9
EFB
filler
content
(phr)
0
65.0 + 0.1
S37
9
10
63.9 + 0.2
20
64.9 + 0.8
S38
9
20
64.5 + 0.3
9
30
65.5 + 0.2
S39
9
30
64.9 + 1.3
9
40
65.6 + 0.7
S40
9
40
64.8 + 0.5
Sample
Acrylic
content
(phr)
S3
9
S21
9
10
S22
9
S23
S24
HDT
(oC)
64.7 + 0.4
177
4.3.2 Glass Transition Temperature
The glass transition temperature (Tg) is an important physical parameter
characterizing amorphous polymers in terms of their chain rigidity and intermolecular
forces. The Tg of S0 showed in Table 4.4 was comparable with the Tg of PVC reported
in the literature (Pedro et al., 2001). Similar to S0, the Tg values of the unmodified filled
composites (S9-S12) and impact-modified filled composites (S21-S24 and S37-S40) in the
Tables 4.4 and 4.5, respectively, recorded as a function of filler content, were also
obtained from the DSC traces. They show a slight increase in Tg with increasing filler
content from 0 to 40 phr. This was predictable since the incorporation of EFB fillers in
PVC-U matrix increased the flexural modulus. Increased in Tg can be explained on the
basis of reduced mobility of chain molecular segments in the vicinity of the filler (Ash
et al., 2002). The physical interactions, due to dipole-dipole interactions, between PVCU matrix and filler provided another reason. However, these interactions were not
strong enough to cause a severe restriction in the molecular segmental motion of PVC.
As discussed in HDT section, the greater softening effect produced by CPE compared
to acrylic can also be observed in the Table 4.5. The Tg values of S37-S40 were slightly
lower than S21-S24.
Table 4.4: Tg of EFB-filled PVC-U composites
S0
EFB filler content
(phr)
0
Tg
(oC)
80.4
S9
10
81.0
S10
20
81.4
S11
30
81.9
S12
40
82.1
Sample
178
Table 4.5: Tg of EFB-filled acrylic-impact modified and EFB-filled CPE-impact
modified PVC-U composites
S7
CPE
content
(phr
9
EFB filler
content
(phr)
0
80.4
81.1
S37
9
10
81.1
20
81.4
S38
9
20
81.1
9
30
82.0
S39
9
30
81.6
9
40
83.1
S40
9
40
82.5
EFB filler
content
(phr)
0
Tg
(oC)
Sample
S3
Acrylic
content
(phr)
9
80.5
S21
9
10
S22
9
S23
S24
Sample
Tg
(oC)
4.3.3 Thermal Degradation Temperature
Figure
4.1
shows
the
thermogravimetric
(TG)
and
differential
thermogravimetric (DTG) curves of neat components degradation, respectively. The
first stage degradation of the neat PVC resin (uncompounded PVC) as shown in Figure
4.1 occurred in the temperature range of 200-400 oC with a peak at 300 oC while the
second stage occurred in the range of 400 –530 oC with a peak at 470 oC. Meanwhile,
for S0 (compounded PVC), its first stage was shifted to the slightly higher temperature
in range of 200-410 oC with a peak at 336 oC while the second stage was in the
temperature range of 410-600 oC with a peak at 500 oC.
The TG and DTG curves of neat PVC resin recorded in this study were also
comparable to the previous findings (Marcilla and Beltran, 1995; Mc Neill et al., 1995).
As mentioned earlier, the researchers have been suggested that the first stage
corresponded to the dehydrochlorination of the PVC with the subsequent formation of
conjugated double bonds. This was considered to be the main reaction and HCl was
assumed to be the major volatile product of degradation. The second stage was
corresponded to the scission of polyene structure sequences formed during the first
179
stage that contributed to the measured weight loss of the PVC resin. A char was
obtained at the end of degradation.
Figure 4.1
(a) TG and (b) DTG curves for neat components
Table 4.6 shows the T5% of the neat components obtained from TG and DTG
curve (Figure 4.1). The onset temperature (T5%) of the S0 was higher than that of PVC
resin while the weight loss of S0 (59 wt %) was lower than the weight loss of PVC resin
180
(64 wt %) as shown in Figure 4.1(a). Similar findings were also reported by other
researchers (Miranda et al., 1999). They found that the weight loss of the suspension
PVC resin at the first stage (200-375 oC) was 64 wt % while Marcilla and Beltran (1995)
found that the weight loss of emulsion PVC resin was 65 wt % in the temperature range
of 227-377 oC. The slightly higher weight loss than the theoretical value was due to the
elimination of low molecular hydrocarbon molecules, which took place simultaneously
with the volatilisation of HCl during this stage (Okieimen and Eromonsele, 2000).
The degradation of S0 also occurred in two stages but its onset temperature was
increased by 14 oC, indicating an improved thermal stability of S0.The total weight loss
at the first stage was similar with stoichiometric amount of HCl of 58.7 wt %. The
similarity was corresponded to HCl volatilisation totally without involving the small
amount of hydrocarbons. A tin heat stabilizer, which was added into the S0, suppressed
the small amount hydrocarbons evolved during pyrolisis as reported by Montaudo and
Puglisi (1991). They reported that the production of benzene and naphthalene was
drastically suppressed by the presence of tin dioxide (SnO2) in the S0, whereas other
aromatics were suppressed to a lesser extent. It means that the crosslinking of the linear
polyene chains formed and transformed directly to char without being able to produce
benzene and other hydrocarbons during the dehydrochlorination process. The
suppression was resulted in the S0 in this study producing a higher residual char (18 wt
%) than PVC resin (8 wt %) after the pyrolisis was completed (Figure 4.1a).
Table 4.6: Degradation temperature of neat components obtained from TG and DTG
curves
Neat Components
Temperature (oC)
Peak 1
300
PVC resin
T5%
281
PVC-U compound (S0)
295
335
500
EFB filler
263
340
none
Acrylic
359
421
none
CPE
287
335
484
Peak 2
470
181
The results of EFB filler degradation are shown in Table 4.6 and Figure 4.1.
Table 4.6 shows that the T5% of 263 oC of EFB filler was the lowest temperature
compared to other neat components. The EFB fillers degraded at this temperature,
which corresponds to the weight loss caused by production and volatilisation of volatile
products. However, based on the DTG curve of EFB filler (Figure 4.1b), there was a
minor peak in the temperature range of 100-200 oC. At this temperature, EFB fillers
were heated above the boiling temperature of water, and thus the moisture content of
EFB fillers evaporated as vapours due to the drying process. The EFB fillers lost their
weight due to the devolatilisation of moisture, approximately 1.2 wt % (Figure 4.1b).
The presence of moisture in EFB filler was also observed in the DSC thermogram as
shown in Figure 4.2. The minor endothermic peak at about 110 oC corresponding to the
heat required for evaporation of moisture in the EFB filler (Thiebaud et al., 1997;
Peters and Bruch, 2001).
Figure 4.2
DSC trace of EFB filler
A more intense peak of DTG implies the maximum rate of weight loss of EFB
filler occurred at 340 oC (Figure 4.1b). Meanwhile, TG curve (Figure 4.1a) shows that
182
only one main step of weight loss of 78 % occurred in the temperature range of 200550 oC and produced 22 % of solid char at 550oC. The thermal degradation of EFB
filler was due to the decomposition of hemicellulose, lignin and cellulose to give off
volatiles. Rowell (1997) reported that the hemicellulose and cellulose degraded by heat
much before the lignin. The lignin component contributes to char formation. Based on
the literature (Nguyen et al., 1981; Thiebaud et al., 1997), as well as from the DSC
studies, (Figure 4.2) the exothermic peaks at 207, 223 and 234 oC can be attributed to
the pyrolisis of hemicelluloses, lignin and cellulose, respectively. The degradation of
EFB fillers started at 250 oC, followed by exothermic peak at 267 oC and 329 oC that
were related to volatilisation/degradation and oxidative combustion of the charred
residues, respectively. The slightly dissimilar results obtained from literature may be
due to the different type of fibre used. According to Saheb and Jog (1999) the chemical
composition of natural fibres varies depending upon the type of the fibre.
Similar to S0, the dehydrochlorination was also the dominant reaction in the
CPE impact modifier degradation. Klaric et al. (2000) reported that the saturated
backbone and partly crystalline structure of CPE were the reasons responsible for the
good thermal stability of CPE before HCl started to evolve. The TG and DTG curve of
CPE in Figure 4.1 also showed two stages of degradation. The first stage occurred in
the temperature range of 200-400 oC with a peak at 335 oC while the second stage
occurred in the temperature range of 400-540 oC with a peak at 484 oC. CPE has better
thermal stability compared to PVC resin because of its maximum weight loss of 35 wt
% in the first stage (Figure 4.1a) whereas PVC resin weight loss was 64 wt %. The CPE
weight loss was almost 36 %, similar to the chlorine content in CPE. Thus, the weight
loss in TG curve could be used to estimate the chlorine contents of CPE (Varma et al.,
1999).
As shown in Figure 4.1a, the TG curve of acrylic impact modifier, which
consists of PMMA shell and PBAC core, revealed that only one stage of degradation
was observed in the temperature range of 250-500 oC with a peak at 420 oC and weight
loss of 97 wt %. However, from the corresponding DTG curve in Figure 4.1b, it
indicated that the one stage of degradation consisted of two stages; the one with the
183
temperature between 250-380 oC corresponded to PMMA. As a shell, PMMA should
be initially subjected to heat compared to the PBAC core during pyrolisis. The other
with the temperature between 380-500 oC corresponded to PBAC (Pavlinec et al.,
1997).
The TG and DTG curves of unmodified filled PVC-U composites (S9-S12) in
Figure 4.3 clearly shows that devolatilisation of moisture of EFB fillers occurred in
temperature range of 100-200 oC for all EFB filler contents even after the EFB fillers
incorporated into the PVC-U matrix. Moisture content in cellulose-containing
composites has also been detected by other researchers (Sapieha et al., 1989). Such
moisture content might play a significant role in degradation processes due to OH
group in water was more reactive the OH group available in the EFB filler (Rowell,
1997).
Table 4.7 shows that T5% decreased progressively with increasing fibre content
while the DTG curves (Figure 4.3b) also changed from two peaks for the S0 to the three
peaks for the S9-S12. Besides, the size of the first peak (maximum rate of weight loss)
also proportionally increased with EFB filler content. Table 4.7 also shows that the
first peaks were largely associated with the degradation of the fillers and were only
marginally related to the PVC-U matrix. Therefore, the temperature range of 200-300
o
C corresponded to the thermal degradation of the EFB filler in the composites, while
the remaining peaks (i.e. the second and third) at about 333-343 oC and 496-505 oC
corresponded to the degradation of PVC-U matrix.
184
(b)
Figure 4.3
(a) TG and (b) DTG curves of unmodified filled PVC-U composites
185
Table 4.7: Degradation temperature of EFB-filled PVC-U composites obtained from
TG and DTG curves
Temperature (oC)
Sample
S0
Filler content
(phr)
0
S9
10
277
271
339
493
S10
20
280
281
342
505
S11
30
276
278
343
496
S12
40
267
278
333
496
T5%
Peak 1
Peak 2
Peak 3
295
336
500
none
As mentioned earlier, the hydroxyl groups in the fillers facilitated extensive
hydrogen bonding between the macromolecules of the filler. Since the moisture in the
unmodified filled composites evaporated during the thermogravimetric test before the
degradation began, the hydroxyl groups of moisture did not influence the degradation.
However, the water molecules released by the fillers during the thermal degradation
significantly affected thermal degradation of unmodified filled composites. The amount
of water released would increase as the filler content increased. Because of their
polarity, the released water molecules would be able of inducing the chlorine atoms of
PVC to cleave from the main chains and undergo dehydrochlorination, as shown in
Figure 4.4. (Naqvi and Sen, 1991; Sombatsompop et al., 2003, 2004).
H2C
PVC molecular chain
CH2
2HC
C
H2C
δ+
δO
+
Hδ
Figure 4.4
Cl
H
δδ+
water molecule
Polar-polar interaction between H20 and PVC molecules
186
Figure 4.5 shows the TG and DTG curves for the CPE-impact modified PVC-U
compound (S7) and EFB filled CPE-impact modified PVC-U composites (S37-S40). As
shown in Table 4.8, the addition of 9 phr CPE into PVC-U increased the thermal
stability of S7 as indicated by theT5% and first peak. The first peak of S7 was shifted to
the higher temperature. The first peak of S7 occurred at temperature of 349 oC, while
the first peak of S0 occurred at 336 oC. This indicates that the interaction between CPE
and PVC in S7, resulting in improvement in the thermal stability of the compound. The
S7 also showed two degradation steps, the first peak was attributed to
dehydrochlorination of PVC and the second peak was attributed to decomposition of
polyene structure sequences formed during the first stage.
The degradation step of S37-S40 also changed from two to three stages when
EFB filler was incorporated. The devolatilisation of moisture content of EFB fillers in
the S37-S40 also occurred in temperature range of 100-200 oC. The first peaks of S37-S40
were also due to the degradation of EFB fillers. As shown in Table 4.8, this first
temperature peak of S37-S40 was relatively similar to the first temperature peak of S9-S12
in Table 4.7.
187
Figure 4.5
TG and (b) DTG curves for EFB-filled CPE-impact modified PVC-U
composites
Table 4.8: Degradation temperature of EFB-filled CPE-impact modified PVC-U
composites
EFB filler
CPE
Temperature (oC)
Sample
content
content
T5%
Peak 1 Peak 2
Peak 3
(phr)
(phr)
S0
0
0
295
336
500
none
S7
9
0
300
349
507
none
S37
9
10
285
273
352
506
S38
9
20
283
285
351
500
S39
9
30
275
278
339
502
S40
9
40
249
254
310
464
Figure 4.6 shows that the thermal degradation of acrylic-impact modified PVCcomposites (S3) was shifted to the lower temperature instead of higher temperature,
even though acrylic impact modifier has good thermal stability (Figure 4.1). The T5% of
S3 was also lower than the T5% of S0. This indicated that the addition of 9 phr of acrylic
decreased the thermal stability of PVC-U matrix. Even though the degradation of neat
188
acrylic impact modifier began at higher temperature compared with PVC-U but it
believed that small methyl methacrylates (MMA) molecules produced from the
depropagation of PMMA reacted with the macromolecules and the radicals formed
during degradation of PVC (Kovacic et al., 1993). The introduction of highly polar
MMA might intensify the undesirable polar tensions, resulting in heat destabilisation.
This polar interaction (similar to Figure 4.4) accelerated by the dehydrochlorination of
PVC, which was activated by the polarisation as illustrated in Figure 4.7.
Figure 4.6
composites
(a) TG and (b) DTG curves for EFB filled acrylic-impact PVC-U
189
δ− O
C δ+
δ−
Cl
O
δ+
H
Figure 4.7
CH3
Polar interaction between MMA and HCl.
Figure 4.6 also shows the volatilization of moisture in the temperature range of
100-200 oC. Similar to DTG of S9-S12 (Figure 4.3), the DTG of S21-S24 also showed
three peaks but all these peaks were shifted to the temperatures lower than the S9-S12
and S37-S40 composites. The first peak at temperature range of 251-258 oC (Table 4.9)
corresponded to the degradation of incorporated EFB filler in the composites while the
major second peak and third peak at 308-320 oC and 460-507 oC, respectively,
corresponded to the dehydrochlorination of PVC-U matrix.
Table 4.9: Degradation temperature of EFB-filled acrylic-impact modified PVC-U
composites obtained from TG and DTG curves
Temperature (oC)
EFB filler
content
(phr)
0
T5%
Peak 1
Peak 2
Peak 3
S0
Acrylic
content
(phr)
0
295
336
500
none
S3
9
0
275
311
469
none
S21
9
10
257
254
320
475
S22
9
20
248
251
314
464
S23
9
30
249
252
315
474
S24
9
40
247
258
308
460
Sample
The T5% of S21-S24 as given in Table 4.9 is lower compared to S9-S12 composites
(Table 4.7). It shows that the combination EFB fillers and 9 phr of acrylic impact
190
modifier actively accelerated the thermal degradation of PVC-U matrix. This may be
attributed to the presence of EFB filler (which contained polar groups) in the composite
had enhanced the concentrations of like-poles in the PVC-U matrix. Such
concentrations, randomly distributed in the PVC-U matrix, may be considered to
constitute weak or high-energy spots and possible sites of initiation of thermal
dehydrochlorination (Naqvi and Sen, 1991).
4.4
Conclusions
The results obtained from the HDT, DSC and TGA analysis in this study, the
following conclusions can be made.
(a)
CPE and acrylic impact modifier slightly decreased the HDT of PVC. CPE has
a greater softening effect than acrylic impact modifier. Thus, the HDT of filled
CPE-impact modified composites was greater than filled acrylic-impactmodified as the impact modifier content increased from 3 to 12 phr. The HDT
of unfilled and filled impact-modified PVC-U was not significantly affected by
the increase of impact modifier contents.
(b)
The HDT of unmodified and impact modified filled PVC-U composites was not
significantly affected by the increase of EFB filler content. The amorphous
structure of PVC and the lubrication effect of silicon oil were attributed to the
insignificant improvement in the HDT of filled composites.
(c)
The Tg of unmodified and impact-modified filled PVC-U composites slightly
increased as the EFB filler contents increased. The restriction of segmental
191
mobility of the polymer chains in the vicinity of the fillers was contributed to
the increment of Tg.
(d)
The incorporation of EFB filler decreased the thermal stability of unmodified
and impact-modified filled PVC-U composites, where the degradation process
has changed from two to three stages. The first stage corresponded to the
degradation of EFB filler, while the second and third stage corresponded to
PVC-U matrix. The maximum rate of weight loss increased with the increase of
EFB filler content.
(e)
The CPE-impact modified PVC–U compound have a good thermal stability
compared to the acrylic impact modified PVC-U compound. The presence of
highly polar of MMA produced from depropagation of PMMA in the compound
intensified
the
undesirable
polar
tensions,
which
accelerated
the
dehydrochlorination of PVC. This dehydrochlorination actively accelerated with
the presence of OH groups of EFB filler, and thus EFB-filled acrylic-impact
modified PVC-U composites have the lowest thermal degradation temperature
compared to other composites.
CHAPTER 5
PROCESSABILITY STUDIES OF PVC-U COMPOUNDS
5.1
Introduction
Torque Rheometer is a useful and widely accepted tool for assessing the state
of PVC fusion. During mixing in a torque rheometer, PVC compound is subjected to
temperature and shear and it passes through all stages of fusion. These stages are
studied by measuring the torque and PVC temperature as a function of time for
constant chamber temperature and rotor speed (Faulkner, 1975).
The fusion process involves a series of particulate changes from larger to
smaller particles followed by fusion of PVC resin primary particles. The fusion
process is affected by a combination of external parameters such as temperature and
shear. Figure 5.1 shows the mechanism of PVC fusion in the torque rheometer
(Allsopp, 1982). PVC resins undergo a compaction and densification process yielding
individual primary particles and primary particles agglomerates, which eventually
fuse together. This route of fusion is a comminution mechanism where PVC grains
are broken down instead of elongated into the primary particles. As mixing continues,
the particulate nature of the melt is gradually eliminated, provided a sufficient
temperature is attained (Allsopp, 1982).
193
Resin grains
compacted
Cold
material
compacted
in chamber
Figure 5.1
Sub-grains and
agglomerates slide
over one another at
minimum torque
High torques
cause some
pulverization
Fusion of
agglomerates and
primary particles
Torque
increases as
interparticle
fusion initiates
and propagates
“Fused” melt of
primary particles
Torque reaches
maximum
Temperature
increases,
torque
decreases
Rigid PVC fusion mechanism in the torque rheometer (Allsopp, 1982).
Since the properties of PVC products depend on the morphology and the
degree of fusion, additives that control the rate of fusion within the processing
equipment become important ingredients in a successful formulation. Many studies
have shown that external lubricants delay the fusion time of PVC compound and
internal lubricants promote the fusion time. But the synergistic reaction between
them has promoted the fusion time of PVC compound significantly (Hawkins, 1982;
Pedersen; 1984; Rabinovitch et al., 1984; Chen et al., 1995). Processing aid, which
used to improve the processing properties of PVC has been recognized as a fusion
promoter, although the mechanism by which this processing aid accelerates the fusion
of PVC has not yet been fully elucidated. According to other researchers, processing
aid has increased the rate of fusion by means of increasing the friction between the
particles (Cogswell et al., 1980; Krzewki and Collins, 1984).
Impact modifier has also been extensively used as an additive in the
commercial PVC formulation with the purpose to improve the toughness properties of
PVC products. Chlorinated polyethylene (CPE) is commonly used as an impact
modifier of PVC. At low content of CPE (less than 10 phr), the fusion time of CPEimpact modified PVC compound has been delayed, whereas the fusion process has
194
been promoted as the CPE content increased. Thus, CPE has dual functions, i.e. as an
external lubricant or processing aid depending on the content used in the formulation
(Chen and Lo, 1999). The acrylic impact modifier, which consists of core and shell, is
another type of impact modifier commonly used in PVC formulations. It promotes the
fusion process of PVC. McGill and Wittstock (1987) found that the primary particles
are broken-down easily when the PVC blended with this impact modifier. During
processing, poly (methyl methacrylate) shell of the impact modifier is capable of
having good interaction with the PVC melts, which promotes the fusion process.
Many PVC compounds are incorporated with filler either to reduce overall
cost or to improve the certain properties of the finished product. Schramm (1965) has
studied the effect of varying the percentage of clay filler in a PVC-U compound. The
fusion rate of the compound decreased with increasing clay filler content. It is also
more difficult to obtain good homogeneity at higher filler loading. The clay filler
occupying the voids between the resin particles restricted the movement of the resin
particles and reduced the flow ability of the compound. A similar trend was also
found by other researchers who studied the effect the rice husk filler loading on the
processability of PVC-U compounds (Azman and Sivaneswaran, 2002).
The processability of PVC compounds, which is determined by the fusion
characteristics, depends on its composition and processing conditions. Although PVC
fusion characteristics have been widely studied by other researchers, no study has
been reported on fusion characteristics of EFB-filled PVC-U and EFB-filled-impact
modified PVC-U compounds. Thus, the main objectives of the study reported in this
chapter are to investigate the influences of EFB filler, and impact modifiers contents
and mixing temperatures on the fusion time and the end torque of PVC-U compounds.
195
5.2
Experimental
In this section, the materials, filler preparation and blend formulation are
similar to Chapter 3. Filler extraction, processability test, and FTIR analysis are
carried out in this study.
5.2.1 Materials and Blend Formulations
The PVC and additives used are shown in Tables 3.1 and 3.2 (Chapter 3). The
blend formulations, S0-S12, S14, S18, S21-S24, S26, S30, S34, S37-S40, S42 and S45 -S48 were
used in this study.
5.2.2 Filler Preparation
The size of EFB fillers and extracted EFB fillers used in this study were less
than 75 µm. EFB fillers were dried in an oven at similar conditions as reported in
Chapter 3, while the preparation for the extracted EFB fillers is described in detail in
the following section.
5.2.2.1 EFB Oil Extraction
According to Han and Rowell (1997), most of plant materials consist of
extractives, holocellulose, lignin, and inorganics (ash). A Soxhlet apparatus (Figure
196
5.2) described by Han and Rowell (1997) was used in this study for EFB fillers
extraction.
The chemical reagent used consists of three types of solvents, which were
ethanol, toluene, and acetone with purity of 99.7, 99.5 and 99.8 %, respectively.
They were mixed in proportion to ratio of four volumes of toluene, one volume of
acetone and one of volume ethanol (Han and Rowell, 1997). These solvents were
employed to extract the oil residues of EFB fillers.
Approximately 31 g of EFB fillers were weighed and placed into preweighed
extraction thimble. The thimble was placed in vacuum oven at 45 oC for 24 hours.
The thimble was cooled in a desiccator for one hour and weighed. Then the thimble
was placed in the Soxhlet extraction unit. The 300 ml of the toluene-acetone-ethanol
mixture was placed in 500 ml round bottom flask with several boiling chips to prevent
bumping. The extraction was then carried out in a well-ventilated chemical fume hood
for 24 hours. The heating temperature of 120 oC was used, which was slightly higher
than the boiling point of toluene. The boiling point of toluene, ethanol and acetone is
111 oC, 79 oC, and 56 oC, respectively. After extraction with solvents mixture, the
thimble was taken out of the extractors, and the excess solvent was drained. The
extracted EFB fillers were washed with ethanol and placed in the vacuum oven
overnight at 45 oC for 24 hours to allow complete evaporation of the ethanol. When
dried, it was removed to desiccators for one hour and weighed.
The collected extract that consisted of extractives and solvents mixture in the
500 ml round bottom flask was condensed using a condensation method in order to
separate the extractives from solvents. The extractives were left in the flask while the
solvents were vaporized and then condensed as a condensate.
197
5.2.3 Dry Blending
Similar to the dry blending process as reported in Chapter 3, the dry blending
process for each blend formulations in this study was done using a heavy-duty
laboratory mixer. All the dry-blended samples were left in desiccators before using
for processability study.
Figure 5.2
Soxhlet extraction apparatus.
198
5.2.4 Processability Study
The fusion characteristics of the PVC-U compounds were determined by using
Brabender Torque Rheometer model PL2200. A 54 gram dry-blended sample was
placed into the mixing chamber through a loading chute. Immediately after powder
has been loaded, the piston with 5 kg weight was inserted in place, and it was pressed
gently to force all the dry blend completely went into the mixing chamber as quickly
as possible (within 20 seconds) for best reproducibility and comparability of test
result. All the dry blends in this study were run at mixing temperature of 180 oC and
rotor speed of 50 rpm. The dry blends, S0, S3, S7, S10, S22 and S38 were also run at 175,
180 and 185 oC at constant rotor speed of 50 rpm. The fusion characteristics of
compounds were studied by observing the changes of torque curve.
5.2.5 Fourier Transform Infra-Red Analysis
The method procedure used for Fourier Transform Infra-Red (FTIR) analysis
in this study was similar as reported in Chapter 3 (Section 3.2.14). The concentrated
extract and condensate for FTIR analysis were injected in between sodium chloride
plates and fitted in the cell unit, while filler and extracted filler were mixed with KBr
to form a thin disc. All these samples were also scanned from 4000 - 370 cm-1 for 16
times.
199
5.2.6 Scanning Electron Microscopy Study
Studies of the filler and extracted filler surfaces were also performed with a
JEOL model JSM-6301F scanning electron microscope (SEM) as reported in Chapter
3 (Section 3.2.13). The purpose of this study is to investigate the surface of filler after
extraction.
5.3 Results and Discussion
The discussion will focus on the influence of EFB filler, acrylic and CPE
impact modifier content, and processing temperature on the processability of
compounds. The effect of extracted EFB filler on the processability will also be
discussed. The lubrication mechanism will be suggested and explained at the end of
this chapter.
5.3.1 Fusion Characteristics
Fusion characteristics such as fusion time, torque at equilibrium stage (end
torque) and maximum torque at fusion, which were obtained from the fusion curve,
were used to elucidate the processability of the studied compounds. Figures 5.3 and
5.4 show a typical fusion curve of PVC-U compound (S0) and EFB-filled PVC-U
composite (S10) melted in the Brabender Torque Rheometer at starting temperature of
180 oC and screw rotor speed of 50 rpm. The compound was discharged when the
stabilized torque reached at 7 minutes. The fusion curve obtained in Figures 5.3 and
5.4 illustrated the changes of viscosity of compound related to torque and temperature
200
versus time. The viscosity-related torque curve showed two different peaks. The first
peak, A, in the torque curve was due to the loading of sample, and the second peak, X,
(fusion peak) was due to the compaction and onset of melting. When the PVC dry
blend was loaded into the system, the initial peak was generated, then the torque
started to decrease sharply because of the free-material flow before it started to
compact; the torque then started to increase and generated the second peak. At this
peak, X, the material has reached an effectively void-free state and started to melt at
the interface between the compacted material and the hot metal surface. The
temperature and torque with respect to this point, X was defined as fusion temperature
and fusion torque, respectively. The time between the loading point A and the fusion
point X was defined as fusion time, t. The compound was in equilibrium state (end
torque) as the torque curve and stock temperature curve being smooth and stable with
time. At this state, the melt was in homogenous.
Stock Temperature
100
o
Torque (Nm)
180
Temprature ( C)
200
80
60 A
X
160
Torque
40
140
20
120
End torque
t
0
-1
100
1
3
5
7
9
11
13
Time (min)
Figure 5.3
A typical temperature and torque curves of PVC-U compound (S0)
blended in the Brabender Torque Rheometer
Stock temperature curve in Figures 5.3 and 5.4 show the generation of
frictional heat during mixing process. Due to the shearing forces of the mixing action,
and the influence of the surface temperature in the mixing chamber and on the rotors,
201
the PVC resin particles of the compound started to soften at the surface. Thus, the
coefficient of friction between the particles when passing each other in the mixing
processing was increased (Schramm, 1965). As a result, the frictional heat in the
system was increased. At the beginning of the test, the stock temperature was
increased due to heat conduction from the heated mixer, afterwards temperature
increased due to transforming work into heat input.
100
220
90
Stock Temperature
Torque (Nm)
70
180
60
50
160
40
Torque
140
30
20
Temprature (oC)
200
80
120
10
0
-1
100
1
3
5
7
9
11
13
Time (min)
Figure 5.4
A typical temperature and torque curves of EFB filled PVC-U
composite (S10) blended in the Brabender Torque Rheometer
5.3.1.1 Effect of EFB Filler
Table 5.1 shows that the incorporation of EFB filler in the compound
decreased the fusion time of PVC-U (approximately 38 % decrement) as the filler
content increased from 0 to 10 phr. The fusion time then remained relatively constant
as the filler content increased from 10 to 40 phr. These results were contradicted with
the results obtained by other researchers. They found that the PVC-U fusion time
202
increased with increasing filler content of clay or rice husk ash. (Schramm,1965;
Azman and Sivaneswaran, 2002).
Unlike clay and rice husk ash fillers, oil residues are present in EFB fillers (as
reported in Section 5.3.3). The presence of oil residue on the EFB fillers has also been
reported by Rozman et al. (2001). Oil residues in the fillers may be able to migrate
onto the filler surface due to the shearing actions of the mixer blades and the frictional
heat during mixing process. This oil residue forms a layer on the outer surface of
EFB filler and tends to be an internal lubricant in the filled compounds. As an internal
lubricant, calcium stearate interacts with the ester components of oil residue to form a
better adhesion that binds the PVC resin particles together easily. As a result, the PVC
resin particles of filled compounds fused at the shorter time. Furthermore, the oil
layer on the EFB fillers surface may also obstruct the thermal heat to be absorbed by
the EFB fillers. Consequently, most of heat was transferred to the PVC resin particles
during mixing process. Another reason for the fusion times of filled compounds were
shorter than PVC-U compound is the frictional heat generated by the friction of fillerfiller and filler-PVC resin particles. The generated frictional heat increased the
thermal heat of the compounds and allowed PVC resin particles to fuse easily.
Table 5.1: Fusion characteristics of EFB-filled compounds at 50 rpm and 80 oC
S0
Filler content
(phr)
0
Fusion time
(s)
96
End torque
(Nm)
31.1
Fusion temperature
(oC)
177
S9
10
60
28.2
175
S10
20
68
27.3
178
S11
30
60
27.5
177
S12
40
58
26.1
175
Sample
As mentioned earlier, the fusion time of filled compounds remained relatively
constant as the filler content increased. This is due to the increase of frictional heat of
203
filled compounds and adhesive property of calcium stearate were probably nullified
by the increase of separation and slipping among PVC resin particles as the filler
content increased. This reason can also be cited to explain the decrease of end torque
and fusion temperature of filled compound (Table 5.1) at 10 phr and remained
relatively constant as the filler content increased from 10 to 40 phr. In general, the
melt viscosity of these compounds decreased with increasing EFB filler content.
5.3.1.2 Effect of Acrylic Impact Modifier
Table 5.2 shows that the fusion time of acrylic-impact modified compounds
(S1-S4) decreased linearly with increasing acrylic impact modifier content. The acrylic
impact modifier, which has PMMA shell, increased the adhesive property of calcium
stearate. The formation of adhesive property in the impact-modified compounds was
more powerful than filled compounds due to the acrylic shell having a greater
compatibility with PVC resin particles. The combined lubrication effect between
acrylic shell and calcium stearate facilitated the PVC resin particles to interact
closely. Consequently, the local friction between the particles, which generated the
frictional heat in the impact modified compounds, was highly enhanced. Therefore,
McGill and Wittstock (1987) reported that a greater degree of interaction between the
PVC primary particles and acrylic promoted the fusion process. The acrylic shell was
also thought to melt first and became a viscous adhesive in the compound. This
viscous adhesive increased the viscosity of the compound, causing a build up in heat
from the shearing process. Besides, it also appeared to perform as a powerful adhesive
that binds the PVC resin particles to fuse together easily. Kosior and Stachurski,
(1986), also reported that the PVC resin particles underwent further shear process as
the acrylic impact modifier content increased which resulted in the increase of resin
particles breakdown and followed by the increase rate of cohesion of primary particles
agglomerates. Based on these reasons, therefore, the fusion time of acrylic-impact
modified compounds in Table 5.2 was decreased approximately 73 % when the
impact modifier content increased from 0 to 12 phr.
204
The end torque values of acrylic-impact modified compounds are interesting
to observe, because the end torque remained relatively constant as the acrylic content
increased. It means that the melt viscosity of these compounds was unaffected with
the increasing acrylic content from 3 to 12 phr. The addition of acrylic in the
compounds was able to promote the PVC resin particles to reach a homogeneous
(equilibrium) melt at the shorter time. In other words, through the process of mixing,
heat transfer from the mixer wall and frictional heat from the inter-particles
interaction, the PVC resin particles increases in temperature at the shorter time, and
eventually the torque increases to a maximum value as the fusion peak since a
coherent melt is observed at this stage. As the mixing continues the temperature
gradually increases due to the fractional heat, causing a faster reduction in torque as
the melt viscosity is decreased (Kosior and Stachurski, 1986). The increase of
frictional heat in the compound at the shorter time resulted in the torque curve capable
to stabilize rapidly and uniformly.
Table 5.2: Fusion characteristics of acrylic-impact modified compounds at 50 rpm
and 180 oC.
Sample
Acrylic content
(phr)
Fusion time
(s)
End torque
(Nm)
So
0
96
31.1
Fusion
temperature
(oC)
177
S1
3
58
30.9
174
S2
6
40
30.3
173
S3
9
30
30.8
171
S4
12
26
31.7
171
Table 5.3 shows the influence of EFB filler contents on the processability of
the filled acrylic-impact modified PVC-U compounds. The result shows that the
fusion time of filled impact-modified compound was not significantly changed at
filler content of 10 phr. It indicates that the filler less inhibited the function of acrylic
as a fusion promoter. This is due to the agglomeration of filler in the filled impact-
205
modified compound were still not predominant. Besides, the frictional heat, which
was generated by the fillers, might also contribute to increase the thermal energy in
the compounds. As a result, the powerful adhesive property of acrylic and calcium
stearate and the generated frictional heat were able to overcome the detrimental effect
of filler and able to bind PVC resin particles together easily and allowed them to fuse
at the shorter time.
Table 5.3 also shows that the fusion time of filled impact-modified compound
was linearly increased as the filler content increased from 10 to 40 phr. The increase
of filler in the compound probably inhibited the ability of acrylic to perform as a
fusion promoter effectively. However, the fusion times of filled impact-modified
compounds in the Table 5.3 were still shorter compared to the fusion times of filled
unmodified compounds as shown in Table 5.1. It indicates that the influence of
acrylic impact modifier in reducing the fusion time of PVC-U compound was more
significant than the oil residue of filler.
Table 5.3: Fusion characteristics of EFB-filled acrylic-impact modified compounds
added with 9 phr of acrylic at 50 rpm and 180 oC
S3
Acrylic
content
(phr)
9
EFB filler
content
(phr)
0
Fusion Time
(s)
End Torque
(Nm)
30
30.8
Fusion
Temperature
(oC)
171
S21
9
10
28
30.7
171
S22
9
20
36
28.4
174
S23
9
30
42
28.6
175
S24
9
40
52
27.9
178
Sample
The acrylic became less effective in increasing the adhesive property of
calcium stearate due to the tendency of EFB fillers to agglomerate among them than
to disperse throughout the compound as the filler content increased. As a result, the
acrylic took a longer time to bind the PVC resin particles together. Furthermore, the
206
increase of filler agglomerations in the compound with increasing filler content was
also increased the separation and slipping among PVC resin particles. As a result, the
transferring of heat to PVC resin particles in the compounds was also delayed. Thus,
PVC resin particles took a longer time to fuse together.
Similar to the fusion time, the fusion temperature of filled impact-modified
compounds in Table 5.3 was increased as the filler content increased. Since the fusion
time of these compounds was increased, it could be explained that more thermal
energy are required to be absorbed by these compounds in order for PVC resin
particles to fuse together. Thus, the fusion temperature was increased and resulted in a
decrease in end torque of these compounds. It shows that the melt viscosity of these
compounds decreased with increasing EFB filler content.
Table 5.4 shows the effect of acrylic impact modifier content on the
processability of the filled acrylic-impact modified PVC-U compounds. The fusion
characteristics of these compounds in Table 5.4 show a similar trend with the results
obtained in Table 5.2 (acrylic-impact modified compounds). The fusion time and
fusion temperature of filled impact-modified compounds decreased and the end torque
remained relatively constant as the acrylic impact modifier content increased from 3
to 12 phr.
Table 5.4: Fusion characteristics of EFB-filled acrylic-impact modified compounds
filled with 20 phr of filler at 50 rpm and 180 oC
27.3
Fusion
Temperature
(oC)
178
60
28.6
177
20
50
28.4
176
9
20
36
28.4
174
12
20
26
29.8
171
S10
Acrylic
content
(phr)
0
EFB filler
content
(phr)
0
Fusion
Time
(s)
68
S14
3
20
S18
6
S22
S26
Sample
End Torque
(Nm)
207
Table 5.4 also shows that the fusion time of filled impact-modified compounds
was progressively decreased to reach the fusion time of the acrylic-impact modified
compounds (Table 5.2) as the impact modifier increased from 0 to 12 phr. The
difference of fusion time between both the filled impact-modified (Table 5.4) and
acrylic-impact modified compounds (Table 5.2) get smaller with increasing impact
modifier content. The fusion time of both compounds was similar at impact modifier
content of 12 phr. It indicates that the presence of 20 phr filler content did not affect
the fusion time of the filled compounds containing 12 phr acrylic impact modifier.
The contribution of acrylic in increasing the particles interaction and frictional heat in
the filled impact-modified compounds allowed the PVC resin particles to fuse at the
shorter fusion time when the impact modifier content increased. The results also
highlight that the influence of acrylic was more predominant than fillers in controlling
the fusion rate.
According to Chen and Lo (1999), the decrease of fusion time resulted in
decreasing the fusion temperature of the PVC compound, due to the less thermal
energy was needed to be absorbed by the compound in order for the PVC resin
particles to fuse together. Because of this, the melt viscosity of PVC compound was
increased. In other words, the melt took a longer time to homogenize and stable when
the torque decreased. Thus, the similar reason can be used to explain a slight increase
in melt viscosity of filled acrylic-impact modified compounds in Table 5.4. Since the
fusion temperature of these compounds was slightly higher, thus these compounds
showed a slight lower in melt viscosity compared to the acrylic-impact modified
compounds (Table 5.2).
Similar to the acrylic-impact modified compounds, the
homogeneous melt of these compounds was achieved rapidly.
5.3.1.3 Effect of CPE Impact Modifier
Table 5.5 shows that the fusion time of CPE-impact modified compounds with
increasing CPE content from 0 to 12 phr. Interestingly, in general, the fusion time of
these compounds decreased as the CPE content increased. The fusion time was
208
significantly decreased when the CPE content reached 12 phr. Similar trend has been
reported by other researchers (Chen and Lo, 1999). Based on the trend of fusion time
shown in Table 5.5, CPE was not very effective to decrease the fusion time at lower
content in range of 0-9 phr. CPE can only perform as a processing aid at 12 phr,
promoting the fusion process of PVC resin particles to occur faster and uniformly.
This also agreed by Chen et al. (2001) in their studies where they found that the CPE
impact modifier did not perform as an effective processing aid at a concentration of
lower than 10 phr.
Table 5.5 also shows that CPE was not effective as the acrylic impact modifier
(Table 5.2) in promoting the fusion time of PVC resin particles. The reduction of
fusion time of CPE-impact modified compound was about only 42 % (compared to
acrylic-impact modified compound which was 73 %) as the impact modifiers content
increased from 0 to 12 phr. The reason is that the CPE is less compatible with the
PVC resin particles, that resulted in less inter-particles interactions to generate the
frictional heat in the compounds. Besides that the combined lubricant effect between
calcium stearate and CPE was probably insufficient to the bind the PVC resin
particles together easily.
Table 5.5: Fusion characteristics of CPE-impact modified compounds at 50 rpm and
180 oC
Sample
CPE content
(phr)
Fusion Time
(s)
End Torque
(Nm)
S0
0
96
31.1
Fusion
Temperature
(oC)
177
S5
3
88
29.4
177
S6
6
90
28.6
178
S7
9
88
28.2
179
S8
12
56
28.4
178
209
As mentioned earlier, the fusion time has a proportional relationship to the
fusion temperature of compound. However, this relationship was found to be not
proportional for the fusion characteristics of the CPE-impact modified compound.
The fusion temperatures remained relatively constant while the fusion time of
compounds decreased as the CPE content increased. This may be that the frictional
heat generated by CPE particles in the compounds did not give enough contribution to
assist PVC resin particles to fuse. A more significant amount of thermal energy was
supplied by the heaters during processing.
Since the fusion temperature was not significantly changed, the end torque of
the compounds decreased marginally as the CPE content increased. This shows that
the homogeneous melt of compounds was also rapidly achieved before seven minutes
of time taken. The end torque values of CPE-impact modified compounds were
slightly lower than acrylic-impact modified compounds (Table 5.2) due to the slightly
longer fusion times and higher fusion temperatures of CPE-impact modified
compounds. In general, the melt viscosity of these compounds decreased with
increasing CPE content.
Table 5.6 shows the fusion time of EFB-filled CPE-impact modified PVC-U
compounds added with 9 phr of CPE. The fusion time of these compounds increased
as the filler content increased from 0 to 40 phr. The fusion times of these compounds
were higher compared to the fusion times of EFB-filled PVC-U compounds shown in
Table 5.1. The decrease in the adhesive property of calcium stearate due to the
addition of CPE caused the fusion time to increase. The ability of CPE in reducing the
adhesive property of calcium stearate has also been reported by Chen et al. (1995).
The predominant effect of EFB filler in increasing the fusion time of the
compounds occurred at 30 and 40 phr filler content. At these filler loadings, EFB
fillers decreased the inter-particles friction among the PVC resin particles in the
compounds by increasing the separation and slipping particles in the compounds. In
this case, EFB filler performed as a fusion delayer for EFB-filled PVC-U compounds
210
with 9 phr of CPE. Since the fusion time was higher, more thermal energy was needed
to be absorbed for PVC resin particles to fuse. This thermal energy resulted in the
fusion temperature becoming higher, since less frictional heat was contributed by the
CPE in the compounds.
Table 5.6: Fusion characteristics of EFB-filled CPE-impact modified compounds
added with 9 phr CPE at 50 rpm and 180 oC
S7
CPE
content
(phr)
9
EFB filler
content
(phr)
0
Fusion Time
(s)
End Torque
(Nm)
88
28.2
Fusion
Temperature
(oC)
179
S37
9
10
80
30.3
180
S38
9
20
82
30.8
180
S39
9
30
150
32.3
186
S40
9
40
160
32.9
189
Sample
In contrast to the previous compounds, the end torque of these compounds
increased as the filler content and fusion temperature increased. It shows that the
homogeneous melt of these compounds could not be achieved within seven minutes.
The delaying of fusion time affected the time taken of PVC resin particles to break
down and stabilize completely in order to achieve the homogeneous melt. Because of
this, the end torque of these compounds increased and was higher than other
compounds. It indicates that the melt viscosity of these compounds increased with
increasing EFB filler content.
Table 5.7 shows the effect of 20 phr of EFB filler on the fusion characteristics of
CPE-impact modified PVC-U. The fusion time increased as the compound added with
3 phr CPE, but remained relatively constant as the CPE content increased from 3 to 12
phr. It shows that the CPE delayed the fusion time of compounds. In this case, it
possible that CPE performed as an external lubricant. Similar trend has been reported
211
by other researchers (Chen and Lo, 1999 and Chen et al.2001). This may be due to
the two factors. The first factor is that the less compatibility between the PVC resin
particles and CPE particles, and secondly the CPE particles decreased the adhesive
property of the calcium stearate.
The fusion temperature of these compounds increased marginally as the CPE
content increased. This shows that CPE did not contribute significantly to the
generation of frictional heat, which can accelerate the fusion process of the PVC resin
particles. The end torque increased as the CPE content increased from 0 to 6 phr and
then remained relatively constant with further increase of CPE content from 6 to 12
phr. The delaying of the fusion process resulted in the end torque of the compounds to
increase slightly. The compounds took slightly longer to completely stabilize and
achieve the homogeneity. The melt viscosity of these compounds also increased with
the addition of CPE.
Table 5.7: Fusion characteristics of EFB-filled CPE-impact modified compounds
filled with 20 phr of EFB at 50 rpm and 180 oC
0
EFB filler
content
(phr)
20
Fusion
Time
(s)
68
End
Torque
(Nm)
27.3
Fusion
Temperature
(oC)
178
S30
3
20
84
28.7
179
S34
6
20
84
30.8
180
S38
9
20
82
30.8
180
S42
12
20
86
30.4
181
Sample
CPE content
(phr)
S10
212
5.3.1.4 Effect of Temperature
Table 5.8 shows the effect of processing temperatures on the fusion time of
compounds. It shows that the fusion time of the compounds decreased as the
temperature increased from 175 0C to 185 0C. The increase of thermal energy due to
the increase of temperatures was attributed to the decrease in fusion time for the
compounds. This thermal energy contributed to the enhancement of PVC chains
mobility that resulted in the rate of primary particles cohesion increased.
Consequently, PVC resin particles fused at a shorter time. Another reason is the
adhesive property of calcium stearate was enhanced significantly as the temperature
increased. The mobile layer, which increased the separation and slipping among PVC
resin particles, caused by the non-polar hydrocarbon chain of calcium stearate and
stearic acid, was also destroyed (Chen et al., 1995; Chen and Lo, 1999; Chen et al.,
2001). Therefore the fusion process of the compounds took place at shorter time at
higher temperature.
Table 5.8: Fusion time of PVC-U compounds at different processing temperatures
and constant rotor speed of 50 rpm
Fusion Time (s)
Sample
S0
S10
S3
S22
S7
S38
EFB filler content (phr)
0
20
0
20
0
20
Acrylic content (phr)
0
0
9
9
0
0
CPE acrylic content (phr)
0
0
0
0
9
9
175
104
88
42
54
94
102
180
96
68
30
36
88
82
185
50
52
18
42
52
78
Temperature (oC)
213
PVC-U compound (S0) took a longest time to fuse at 175 0C compared to other
compounds due to the calcium stearate and stearic acid in the PVC-U compound were
able to develop a mobile layer. This mobile layer resulted in the increase of fusion
time since less mechanical energy during mixing process was converted to thermal
energy (Chen et al.,1995; Chen and Lo,1999). This reason can also be used to explain
the longer fusion time of the EFB-filled CPE-impact modified PVC-U composite
(S38). The fusion time of PVC-U compound at 185 0C was almost similar to the fusion
time of EFB-filled PVC-U composite (S10) and CPE-impact modified PVC-U
compound (S7). In this case, calcium stearate in these compounds performed as a
processing aid due to its adhesive property was increased at this temperature.
Table 5.8 also shows that the fusion time of acrylic-impact modified PVC-U
compounds (S3) at 185 oC was the shortest compared to other compounds. The
synergistic combined lubricant between calcium stearate and acrylic impact modifier
was able to form a powerful viscous material, which appeared to act as an adhesive
that allowed the PVC resin particles to fuse together easily. Since the fusion time of
acrylic-impact modified compounds was the shortest compared to other compounds at
all temperatures, it can be deduced that the acrylic impact modifier is the most
efficient additive in reducing the fusion time of PVC-U compounds and followed by
the EFB filler and then CPE impact modifier.
Table 5.9 shows the end torque of PVC-U compounds with varying processing
temperatures. In general, the end torque decreased as the temperature increased. The
higher temperature did not only reduce the fusion time but also decreased the melt
viscosity of the compounds. The reduction of viscosity was attributed to the greater
molecular mobility due to the higher thermal energy supplied for the PVC particles
resin during mixing process.
Table 5.9 also shows that in general the end torque of EFB-filled CPE-impact
modified compounds was the highest at all processing temperature. It means that the
combination between EFB and CPE increased the melt viscosity of compound. This is
214
may be due to the combined lubricant effect between EFB and CPE had increased the
time taken of the compound to fuse and stabilize completely and formed a
homogeneous melt. The end torque of unfilled CPE-impact modified compound at
185 0C was the lowest. It shows that the CPE was effective in reducing the melt
viscosity of compound at this temperature.
Table 5.9: End torque of PVC–U compounds and composites at different
temperatures and constant rotor speed of 50 rpm
End Torque (Nm)
Sample
S0
S10
S3
S22
S7
S38
EFB filler content (phr)
0
20
0
20
0
20
Acrylic content (phr)
0
0
9
9
0
0
CPE acrylic content (phr)
0
0
0
0
9
9
175
29.7
30.5
31.6
32.3
29.0
32.0
180
31.1
27.3
30.3
28.4
28.2
30.8
185
27.7
26.2
29.5
28.0
25.1
30.0
o
Temperature ( C)
5.3.2 Postulated Lubrication Mechanisms
The concepts of lubricant mechanisms, similar to Robinovitch et al. (1984)
and Chen et al. (1995) as shown in Figure 2.8 (Chapter 2), are proposed based on the
present study. Previous studies have used the paraffin wax or polyethylene oxide and
CPE as an external lubricant and impact modifier, respectively. In this study, the
stearic acid, acrylic, and EFB were used as the internal lubricant, impact modifier, and
filler, respectively. Thus, a slight addition and modification on the previous
lubrication mechanisms was done.
215
PVC is known as a polar thermoplastic polymer due to the presence of C-Cl
groups in its molecular chains. Because of this polarity, the molten PVC is attracted
and stuck to the polar metal surface of processing equipment (Figure 5.5a). As
mentioned in Chapter 2 (Section 2.2.2), the strong polar ends of calcium stearate
molecules adhere to the polar PVC and also the polar metal surface, and leaving the
non-polar tails to perform the lubrication. The non-polar tails of calcium stearate
displace the PVC melt from sticking on the metal surface and providing limited slip
between the metal and PVC melt surfaces (Figure 5.5b). The polar groups in calcium
stearate are also strongly attracted to each other and form a viscous layer structure,
which is similar to a liquid crystal (Figure 5.5b)(Chen et al., 1995).
The stearic acid with HCOOC groups, which was used as an external lubricant
in this study, is also polar material. Therefore, in the presence of stearic acid, the polar
groups of stearic acid will also attach to the metal surface, to the surface of PVC resin
particles, and to each other, while the long-chain aliphatic acid provides the
lubrication effect. The combined interaction between calcium stearate and stearic acid
in the compound is also illustrated in Figure 5.5b. The external lubricants, however,
have a lower polarity than the internal lubricants (Marshall, 1969). Thus, the ability of
calcium stearate to hold PVC resin particles together in the compounds is better than
stearic acid.
The acrylic impact modifier is known to be highly compatible with PVC. The
polarity of PMMA in the acrylic shell is higher, thus a better interfacial adhesion
(compatibility) between PVC particles and acrylic shell is formed. The interaction
between acrylic shell and PVC is also well distributed (Figure 5.5c) due to the ability
of acrylic to disperse in PVC matrix (Lutz, 1993). Therefore, acrylic shell acts evenly
as a bridge and appears to increase the number of ties between the PVC particles. The
acrylic core remains in between PVC particles. It acts as a grit to increase the
frictional heat in the compound (Figure 5.5c). The acrylic shell is also attracted and
stuck to the metal surface. Due to the polarity, the acrylic shell attracted to the
calcium stearate to form a powerful adhesive property to bind the PVC particles
together (Figure 5.5f).
216
In contrast with acrylic, the interaction between CPE and PVC resin particles
is insufficient to hold the PVC particles together due to it less compatible to PVC
(Figure 5.6c). Due to the C-Cl group in the molecular chains, CPE is also attracted
and attached to the polar metal surface. The shorter fusion time and higher melt
viscosity for acrylic-impact modified compounds (Table 5.2) compared to CPEimpact modified compounds (Table 5.5) may be traced to two possible factors: (a)
good compatibility and dispersion and (b) combined lubricant effect with calcium
stearate.
The EFB is a highly polar filler. Although the polarity of EFB filler makes
them capable of forming a physical interaction with polar PVC (Woodham et al.,
1995), it is a relatively weak interaction compared to the strong filler-filler interaction
caused by hydrogen bondings. Therefore, EFB fillers have a greater tendency to
attract among themselves to form the filler bundles and leave in between the PVC
particles (Figure 5.5d). Thus, there is a slight attraction between EFB fillers surface to
the PVC particles. In this case, there are two significant factors that can be contributed
by EFB filler. The first factor is it increases the frictional heat and the second factor
is it increases the separation among PVC resin particles especially at higher filler
loading (Figure 5.6g). Interestingly, the two factors can give opposing effect to the
fusion time of PVC-U compound. Due to the polarity, the EFB fillers are attracted to
calcium stearate, acrylic, and CPE (Figure 5.5g and Figure 5.6g). The ability of EFB
filler to increase the frictional heat and interact (due to the presence of ester
component of oil residue) with calcium stearate to form a fairly good adhesion
between PVC resin particles were the factors responsible for the shorter fusion of
EFB-filled compound (Table 5.1) compared to CPE-impact modified compounds
(Table 5.5). The increase of separation among PVC resin particles contributed by
agglomeration of fillers, resulted in the melt viscosity of EFB-filled compounds to be
lower than acrylic (Table 5.2) and CPE-impact modified compounds (Table 5.5).
217
(a)
METAL
1µm PVC
microparticle
flow unit
PVC
PVC
calcium stearate and stearic acid
(b)
METAL
acrylic core-shell impact modifier
(c)
METAL
EFB filler bundles (agglomerates)
(d)
METAL
(e)
METAL
(f)
METAL
(g)
METAL
Figure 5.5
Postulated lubrication mechanism of among PVC micro-particles flow
units, EFB fillers and acrylic impact modifiers
218
(a)
METAL
1µm PVC
microparticle
flow unit
PVC
PVC
calcium stearate and stearic acid
(b)
METAL
CPE impact modifier
(c)
METAL
EFB filler bundles (agglomerates)
(d)
METAL
(e)
METAL
(f)
METAL
(g)
METAL
Figure 5.6
Postulated lubrication mechanism of among PVC micro-particles flow
units, EFB fillers and CPE impact modifiers
219
5.3.3 Effect of Extracted EFB Filler on the Processability of PVC-U Compound
In this section, the processability of extracted EFB filler-filled compounds
with difference filler content was investigated. The analysis of extracted filler,
concentrated extract and solvents condensate using FTIR and SEM are reported.
5.3.3.1 Extractives Removal
The percentage of extractives removed from the EFB filler was approximately
4.5 %. The effect of extraction on the appearance of solvent mixture was studied by
the visual inspection. The solvents mixture changed in colour from plain to dark
brown, while the extracted fillers were found to be brighter in colour than the
unextracted fillers. This visual inspection indicates that the extraction has effectively
extracted the extractives, which include oil residues of fillers. The analysis on the
extractives and extracted fillers was carried out to verify that the extraction was
successfully achieved.
5.3.3.2 FTIR Spectra
The cellulose molecular structure as shown in Figure 2.11(Chapter 2) is useful
for functional groups identification in the EFB filler. FTIR analysis was done on the
fillers, concentrated extract, and condensate. Figure 5.7 shows the FTIR spectrum of
extracted and unextracted EFB filler. Both spectrums were found to be very similar. It
shows that the functional groups of the extracted and unextracted filler cannot be
distinguished using this analysis.
Both spectrums show a broad peak at 3393 and 3391 cm-1 due to absorption
vibration of the hydroxyl (OH) group (Sarani et al., 2001). The peaks at 2919 and
220
2916 cm-1 are due to the stretching of C-H groups. The presence of cellulose is
obviously seen from the sharp peak appearing at 1730 and 1731 cm-1. This is due to
the stretching vibration of carbonyl group (C=O). Peaks at 1629 cm-1 and 1630 cm-1
are an indicative of the presence of lignin, an aromatic compound, and due to the C=C
vibration of benzene ring.The broad peaks (both spectra) at 1050 and 1050 cm-1 are
assigned to ether linkage (C-O-C) from lignin or hemicelloluse (Matuana et al.,
2001).
Figure 5.7
FTIR spectra: a) EFB filler b) extracted EFB filler
Figure 5.8 shows the FTIR spectrum of concentrated extract and solvent
condensate. By using the palm oil molecular structure as a reference (Figure 5.9), the
existance of ester component in the concentrated extract was clearly detected. The
sharp absorption band appearing at 1712 and 1739 cm-1 are attributed to the stretching
of carbonyl groups (C=O). The sharp absorption band at 1261 cm-1 is due to
221
asymmetric stretching of C-O-C from the oil chemical structure (Conley, 1972). Since
the oil chemical structure contains a long chain of hydrocarbon, thus the sharp and
strong band at 2925 and 1458.87 cm-1 due to the stretching of C-H groups and
bending of CH2 groups, respectively, are clearly observed (Streitwieser and
Heathcook, 1981).
This spectrum confirmed the existence of oil residue in the
concentrated extract.
Figure 5.8
FTIR spectra (a) solvents mixture condensate (b) concentrated extract
222
H
O
C
O
C16H31
Palmitic
H C O
C
O
C17H35
Stearic
H C O
C
C17H35
Stearic
H
C
O
H
Figure 5.9
Palm oil molecular structure
5.3.3.3 Extracted Filler Surface
By visual observation, the extracted EFB fillers were brighter in colour
compared to the EFB fillers. Both fillers were also analyzed using SEM to see the
effects at higher magnification. Figures 5.10 and 5.11 show the SEM micrographs of
unextracted and extracted filler surface, respectively. The surface of the extracted
filler was coarser than the unextracted. It was also observed that the extracted filler
surface contained a lot of pits. The difference is believed due to the removal oil and
other extractives from the extracted filler surface.
223
Smoother Surface
Figure 5.10
SEM Micrograph for EFB filler (Magnification 3000x)
Coarser Surface
Figure 5.11
SEM micrograph for extracted EFB filler (Magnification 1000 x)
5.3.3.4 Fusion Characteristics of Extracted EFB Filled PVC-U Compound
Table 5.10 shows the effect of extracted EFB filler content on the fusion
characteristics of extracted filler-filled PVC-U compound. Similar to the unextracted
fillers, the fusion time of extracted fillers of filled compounds is shortened than the
unfilled compounds.
224
Table 5.10 also shows that the fusion time of extracted filler filled-compound
decreased drastically upon the incorporation at 10 phr and increased linearly with
further increase of filler content from 10 to 40 phr. It shows that the extracted filler
was also able to reduce the fusion time of filled compound. Based on the fusion time
of unextracted filler-filled compounds in Table 5.1, the extracted filler-filled
compound took a shorter time to fuse compared to the unextracted filler as the filler
content increased from 10 to 20 phr. It showed that the coarser surface of fillers
(Figure 5.11) was more effective to enhance the frictional heat of filled compounds
compared to unextracted fillers. As the filler content increased from 30 to 40 phr, the
separation and slipping among the PVC resin were also increased. The lack of oil
residues resulted in the adhesive property of calcium stearate additive became weaker
as filler content increased. Therefore, calcium stearate took a longer time to bind PVC
resin particles together in extracted filler-filled compounds. Consequently, the fusion
time of extracted filler-filled compounds increased and slightly higher than the
unextracted filler-filled compound as filler content increased from 30 to 40 phr.
Since the fusion time increased, the fusion temperature also increased and
resulted in the end torque of the compound to decrease. The slightly higher end torque
of these compounds compared to unextracted filler-filled compounds in Table 5.1 is
due to extracted fillers not being coated with oil residues. It elucidates why the melt
viscosity of the extracted filler-filled compounds was lower than unextracted filler.
Table 5.10: Fusion characteristics of extracted EFB-filled PVC-U compounds at 50
rpm and 180 oC
S0
Extracted
filler content
(phr)
0
Fusion
time
(s)
96
End
torque
(Nm)
31.1
Fusion
temperature
(oC)
177
S45
10
44
30.8
176
S46
20
58
27.5
177
S47
30
66
27.7
178
S48
40
78
27.0
180
Sample
225
5.4
Conclusions
The main objective of this chapter is to investigate the effect of EFB filler,
acrylic and CPE impact modifier, and temperatures on the fusion characteristics of
PVC-U compounds. Based on the results obtained, several conclusions can be drawn:
(a)
The fusion time of PVC decreased as both the EFB filler and extracted EFB
filler were incorporated. However, the fusion time of EFB-filled PVC-U
composite remained relatively constant as the filler content increased from 10
to 40 phr. The frictional heat generated by the filler and followed by the
increase of the adhesive property due to the synergistic combined lubricant
between of calcium stearate and oil residue probably nullified by the increase
of separation among PVC resin particles. The fusion time of extracted EFB
filler-filled compound increased with increasing filler content from 10 to 40
phr. The increase of separation and slipping among the PVC resin particles
and the lack of oil residues weakened the adhesive property of calcium
stearate. The weakened calcium stearate was attributed to the increase of
fusion time.
(b)
The acrylic impact modifier performed as a fusion promoter for all compounds
whereas CPE changed from a fusion promoter to a fusion delayer in the
formulations contents of 9 phr CPE and 30 phr or 40 phr EFB filler. The
fusion time of PVC compound added with 9 phr acrylic at 185 oC is the
shortest while the longest fusion time is produced by the PVC compound
added with 9 phr CPE and 40 phr EFB filler at 180 oC.
(c)
The incorporation of EFB filler decreased the melt viscosity of the
compounds.
The melt viscosity of EFB-filled compound is the lowest and
followed by the extracted filler-filled compound. The PVC-U compound
226
containing 9 phr CPE and 40 phr EFB at 180 oC produced the highest melt
viscosity.
(d)
The increase of processing temperature decreased significantly the fusion time
and melt viscosity of the compounds due to the increasing of thermal energy.
(e)
The lubrication mechanisms of the studied compounds have been postulated.
Due to the polarity of molecules, calcium stearate was able to interact
effectively with PVC. This result in a strong adhesion, which binds the PVC
resin particles together and cause them to fuse at a shorter time. On the other
hand, the increase in fusion time with increasing filler content is due to the
increase of separation and slipping among the PVC resin particles.
CHAPTER 6
EXTRUSION PROCESS AND MECHANICAL PROPERTIES OF
EXTRUDATES
6.1
Introduction
As an amorphous thermoplastic polymer, PVC does not exhibit a distinct
melting point but gradually soften above its glass transition temperature. The
extrusion process consists of softening the PVC by heat, fusing it together and forcing
it through a die of the required dimensions, followed by cooling of the melt in order to
retain the shape.
The mechanical properties of PVC-U extrudates produced by single screw
extruder have been studied by Covas and Gilbert (1992). In their study, the effect of
fusion on the mechanical properties of extrudates has been investigated. Owing to the
significant level of shear present in single screw extrusion, the route to fusion seems
to be different from that observed in twin screw extrusion. Therefore, the hypothesis
for the fusion of PVC-U compounds in single screw extruder has been developed
from that originally derived by Allsopp (1982).
The mechanism of fusion is
illustrated in Figure 2.4 (Chapter 2). The melting of solid materials occurred either by
comminution of grains with internal structure substituting or by ruptures of internally
228
fused grains. In other words, the comminution, compaction and internal fusion of
grains could be observed simultaneously in the extruder machine. Progressive fusion
and gradual increase in melt homogeneity were postulated. Network structures of
entanglements, primary and secondary crystalline were also present upon cooling.
It is well known in the PVC profile extrusion industries that the mechanical
properties of the product are related to the shear and temperature during extrusion.
The fusion process of PVC is strongly influenced by these two factors. Increasing
shear in the extruder can be done by increasing the screw speed. However, the
residence time decreased counteracting the effect of the shear increased. In the
previous study, Summers (1982) found that the morphology and toughness of a PVC
compound in single screw extrusion was only slightly affected by shear rate but
dominated by melt temperature. The toughness of PVC compound went through a
maximum then decreased with further increasing of melt temperature. The decrease of
this toughness was due to the failure of lubrication system, which resulted in the melt
fracture on the extrudates. The similar observation has also been reported by Lacatus
and Rogers (1986). They found that the optimum toughness of extrudate was obtained
at melt temperature of 177 oC (at lower fusion level). At 204 oC, the melt fracture of
the extrudates which was the reason for the toughness decreasing.
Other researchers also studied the effect of fusion on the tensile and impact
properties of extrudates. Covas and Gilbert (1992) reported that the yield parameters
were insensitive to the level of fusion whereas the impact strength increased with
increasing of the level of fusion and exhibited a maximum value. Similar results have
also been extensively reported by other researchers (Benjamin, 1980; Uitenham and
Geil, 1981; Terselius and Jansson, 1981, 1984, 1985). They concluded that in order to
obtain the optimum mechanical properties, an appropriate level of fusion was needed.
It means that although during processing the original PVC grains particles was
progressively changed into a network of entanglements, primary and secondary
crystallinity, but the presence of some remaining primary particle was required in
order to achieve the optimum properties.
229
Despite the known effect of fusion level on the mechanical properties of PVC,
a limited number of studies have been carried out on the influence of screw speed and
processing temperature on the fusion level and mechanical properties of the EFBfilled PVC-U extrudates. With this in mind, the main objective is to study the
mechanical properties of unfilled and filled extrudates after being extruded using a
single screw extruder.
6.2
Experimental
In this section, the materials and blend formulations used are similar to Chapter 3
(Section 3.1). The dry blending, extrusion processing, mechanical testing, and DSC
analysis are described.
6.2.1 Materials
Six blends formulations were prepared for this study. The blend formulations,
namely PVC-U compound (S0), acrylic-impact modified PVC-U (S3), CPE-impact
modified PVC-U (S7), EFB-filled PVC-U (S9 and S10) and impact modified EFBfilled PVC-U composites (S21, S22, S37 and S38) as shown in Table 3.3 (Chapter 3)
were used. 12 kg of each formulation was prepared to meet the requirement of
extrusion process.
230
6.2.2 Dry Blending
The formulations were dry blended using a Lab-Tech 5L high-speed mixer of
the impeller type and water-jacketed. The formulations were dry blended in 4 kg
batches, using the following sequence: 1 min at low speed and followed by another 1
minute at high speed. The temperature was built up during mixing process, due to the
generation of frictional heat, thus the blend was discharged from the mixer chamber
after 2 minutes blending in order to avoid the temperature exceeding 60 oC. Above this
temperature, the blend became sticky and stuck on the mixer chamber wall and
impeller.
6.2.3 Extrusion Process
Each PVC-U dry blend was oven dried at 105 oC for 24 hours before they
were compounded on a single screw extruder at two conditions as shown in Table 6.1.
For the first condition, the extrudates were extruded at constant screw speed with
difference processing temperatures. The extrudates were also extruded at constant
temperature with difference screw speeds as a second condition. The ratio of the
length of the flighted portion of the screw to the outside diameter of the screw flights
(L/D) was 27:1. The slit die with 1.5 mm in aperture and 100 mm in width was
attached to the extruder. The extrudate in the stripe form with approximate dimension
of 2.4 mm in thickness and 100 mm in width was cooled in the ambient temperature
after leaving the die. The extrudates were firstly cut into bars using a band saw
machine before they were shaped according to the test specimens using the templates
and cutting machine. The cutting sides of specimens test were polished with a sand
paper before carrying out the mechanical testing.
231
Table 6.1: The conditions of extrusion processing
Screw Speed
(rpm)
60
Feed Zone
160
Constant Screw Speed
Processing Temperature (oC)
Compression Zone
Metering Zone
170
180
Die
180
60
165
175
185
185
60
170
180
190
190
60
175
185
195
195
Constant Processing Temperature
50
160
170
180
180
60
160
170
180
180
70
160
170
180
180
6.2.4 Izod Impact and Flexural Testing
The dimensions of the test specimens for the impact and flexural testing were
similar to the ones reported in Chapter 3 (Sections 3.2.9-3.2.10) except for the
specimen thickness. The average thickness of the specimen used for both testing was
2.4+0.2 mm. The notched specimens were impact tested in the Izod mode using a
Toyo-Seiki Pendulum Impact Tester with impact velocity of 3.0 m/s and 150o swing
angle using a 31.87 N hammer at room temperature. The machine and method used
for the flexural testing were also similar to Chapter 3 (Section 3.2.10). The reported
values for the testing were average of seven specimens.
232
6.2.5 Tensile Testing
The tensile properties, in accordance with the ASTM D638-91(Type 1)
method, were measured using a Lloyd Instrument model EZ20 (cell load of 20 kN)
with four variations of crosshead speed, namely of 5, 20, 80 and 100 mm/min. The
specimen dimensions used were 2.4+0.2 mm in thickness, while the gauge length
used was 60 mm. The reported values for the test were also average of seven
specimens.
6.2.6 Differential Scanning Calorimetry Study
A Mettler Toledo Differential Scanning Calorimetry (DSC) instrument model
821 as reported in Chapter 4 (Section 4.2.4) was also used in this study. The similar
experimental procedure was also utilized for this study. The extrudates that were
processed at difference processing temperatures were analysed to determine the heat
of fusion.
6.3
Results and Discussion
In this section the influence of extruder screw speeds and processing
temperatures on the impact, flexural and tensile properties of extrudates will be
discussed. This section will also highlight the relationships between the processing
temperatures and heat of fusion. The die temperature as already shown in Table 6.1
will represent the processing temperatures.
233
6.3.1 Extrudates Characteristics
The blend formulations of S0, S3, S7, S9 and S21 were extruded using a single
screw at the processing conditions as shown in Table 6.1. The extrudates with smooth
surfaces were produced in this study are shown in Figure 6.1.
Figure 6.1
Extrudates of S0, S3, S7, S9 and S21 at die temperature of 185 oC, and
extrudate of S37 at die temperature of 190 oC
Although the dimension of slit die used was 1.5 mm x 100 mm, the
dimensions of extrudates produced were slightly larger due to the swelling of
extrudates as it exited the slit die. This phenomenon is called die swell and illustrated
in Figure 6.2. The die swell was caused by the viscoelastic nature of the polymer melt
that dissipates forces slowly. The compressive forces that were needed to push the
polymer melt through the land and small die were not completely relieved by the time
the polymer exits the die. Therefore, the polymer expanded when it exited the die in
response to the residual compressive forces. The die swell resulted in the extrudate
surface being slightly curved at the top and flat at the bottom. The auxiliary
234
equipment attached with 1.85 kg rotating roller was used to haul off the melt from the
extruder in order to minimize the die swell.
Extrudate (top surface)
Slit Die
Figure 6.2
Shape difference between the die and extrudate
Unlike other extrudates (S0,S3,S7,S9,S21), the extrudate of S37 which contained
10 phr EFB and 9 phr CPE were severely distorted shortly after exiting the slit die at
die temperature of 180 0C and 185 0C (Table 6.1). The distorted extrudate is known as
a bambooing defect (a type of melt fracture), which can be seen in Figure 6.3. It might
be that the fusion time of S37 which contains CPE and EFB fillers are relative long
during extrusion and some of the PVC remained in particulate form, resulting in an
increase of melt viscosity. As the melt was flowing, it developed a flow profile with
the centre of the melt flowing faster than the edges, because of the friction of the melt
against the edges of the die. The melt in the centre of the flow slid against itself easier
than it slid against the die walls. Because of the difference in velocity between edges
and centre, as the melt lef the die, it was distorted somewhat like a bamboo. This also
generated tensile stress and if the stress exceeds the melt strength, the edges of
extrudate rupture causing the defect. The bambooing defect and the ruptured edges of
S37 are shown in Figure 6.3. The defects were eliminated as the die temperature
increased to 190 oC (Figure 6.1) and 195 oC, whereby the extrudates with smoother
surface were produced. It indicates that at these temperatures the melt viscosity of S37
was reduced, as a result of the sufficient fusion process taking place (Strong, 2000).
235
Figure 6.3
Filled extrudates of S37 at die temperature of 180 oC and 185 oC and at
constant screw speed of 60 rpm.
Before the extrusion, the dry blends were oven dried and left to cool for a few
minutes in the closed oven before being used for extrusion processing. If the drying
process was insufficient, the air bubbles generated from the moisture of dry blends
were formed during extrusion. Since the vent port was unavailable at the compression
zone of the extruder, the air bubbles was unable to escape during the transition
process of solid phase to melt phase. Shortly after the melt exited from the die, the air
bubbles inside the melt started to move up to the top of the surfaces. Consequently the
extrudates with air bubbles on the surface were produced. The air bubbles randomly
distributed on the extrudates surfaces were observable as shown in Figure 6.4.
236
Figure 6.4
Filled extrudate of S9 with air bubbles on surface
Rough surfaces were observed on the extrudates incorporated with 20 phr EFB
(S10, S22 and S38). The roughness of these filled extrudates was greatly noticeable at
the bottom surface. To eliminate this defect, the screw speed was increased up to 100
rpm at constant die temperature of 195 oC. However, no significant changes were
observed on the quality of extrudates surfaces produced as shown in Figure 6.5. Based
on the visual inspection on the filled extrudates surface, it was found that EFB fillers
were poorly distributed and poorly dispersed throughout the matrix. The fillers
precipitated at the bottom surface due to the EFB being slightly denser than PVC resin
(as reported in Chapter 3). The small L/D ratio of the screw used in this study is also
one of the reasons to explain the occurrence of the surface defect. The L/D is a
measure of the ability of the screw to mix materials with high L/D ratio promoting
good mixing and good melting capabilities (Strong, 2000). Thus, in PVC extrusion,
high L/D ratio is required to ensure the dry blends have sufficient residence time for
homogeneous mixing and melt before leaving the die. The results showed that the
L/D ratio (27:1) of the screw used in this study was not sufficient to produce good
quality filled extrudates containing 20 phr EFB filler.
237
Figure 6.5
Filled extrudates of S10, S22 and S38 at die temperature of 195 oC.
Tables 6.2 and 6.3 show the residence time of extrudates at constant die
temperature of 180 oC and at constant screw speed of 60 rpm, respectively. Table 6.2
shows that the residence time decreased as the screw speed increased from 50 to 70
rpm. On the other hand, the residence time of the extrudates was not significantly
changed as the processing temperature increased at constant screw speed (Table 6.3).
These results show that the residence time was strongly dependent on the screw speed
used during extrusion as the drag force increased.
Table 6.2: Residence time of extrudates at constant die temperature of 180 oC
Residence Time (s)
Speed (rpm)
So
S3
S7
S9
S21
50
60
62
63
61
63
60
55
53
54
53
50
70
41
43
42
43
44
238
Table 6.3: Residence time of extrudates at constant screw speed of 60 rpm
Residence Time (s)
Tdie (0C)
So
S3
S7
S9
S21
S27
180
55
53
54
53
53
-
185
53
57
56
54
50
-
190
54
58
57
55
53
60
195
53
58
58
53
53
55
6.3.2 Differential Scanning Calorimetry
It has been reported that the differential thermal analysis can be used to
evaluate the level of fusion of processed PVC samples (Gilbert and Vyvoda, 1981;
Gilbert, et al. 1983). On reheating a sample of processed materials, melting of the
secondary crystalline, which contributed to network development, might be detected.
The detected endotherm in the DSC thermogram represented the melts of secondary
crystallite.
A typical thermogram for the unfilled PVC-U extrudate at difference
processing temperatures is shown in Figure 6.6. It can be seen that the area of the
endotherm, which represents a secondary crystallite population generated during
cooling, increased with increasing processing temperature. This is in agreement with
the results obtained by other researchers for the processed PVC compound (Gilbert
and Vyvoda, 1981; Gilbert, et al. 1983; Cora et al.1999). The energy (heat of fusion)
of the endotherm increased with processing temperatures, due to the increase of
breakdown of secondary crystallites. The increase of endotherm also indicated the
number of primary particles melts increased. Thus, the heat of fusion obtained from
the endotherm was also related to the level of fusion. Similar results on the increase of
239
endotherm area with increasing processing temperature were shown by other
extrudates.
The other interesting and useful information available in DSC analysis is that
the endotherms end-point temperatures of extrudates were equal to the maximum
processing temperature used in the extrusion processing. This is a valuable internal
measure of processing temperature (Gilbert, 1985). Interestingly, the results in Figure
6.6 confirm that maximum processing temperatures indicated by the DSC analysis
were similar to the real die temperature during extrusion.
End-point
exo
195oC
Heat Flow
End-point
190oC
185oC
End-point
180oC
End-point
Figure 6.6
A typical DSC thermogram of S0 at different processing temperatures
Table 6.4 shows the heat of fusion of extrudates increased with increasing
processing temperature, which indicates the degree of fusion increased with
increasing processing temperature. A similar observation has been reported by other
researchers (Benjamin, 1980; Gilbert et al., 1983; Axtell et al., 1994). It was found
240
that both EFB filler and acrylic acted synergistically in S21 to generate the highest heat
of fusion at all processing temperatures. There are two reasons, namely the frictional
heat generated by fillers and the ability of acrylic to accelerate the fusion process
which were attributed to the increase of heat input of PVC to undergo fusion process.
These reasons were strongly supported by the higher of heat of fusion S3 and S9
compared to S0. Table 6.4 also shows that the addition of CPE into S7 has a similar
effect as acrylic in increasing the PVC heat of fusion, even though it was not as
effective as acrylic. The effectiveness of acrylic to accelerate the fusion process of
PVC compared to CPE has been discussed in previous chapter.
Table 6.4: Heat of fusion of extrudates at screw speed of 60 rpm
Heat of Fusion (J/g)
S7
S9
2.68
1.91
Tdie
(oC)
180
S0
2.23
S3
4.15
185
2.53
5.81
2.93
190
2.82
5.49
195
5.71
5.93
S21
4.52
S37
-
4.49
8.02
-
4.72
4.72
9.05
4.89
4.82
7.73
9.38
6.92
6.3.3 Impact Strength
6.3.3.1 Effect of Processing Temperature
Table 6.5 shows the effect of processing temperatures on the impact strength
of extrudates at screw speed of 60 rpm. The result shows that all extrudates underwent
complete fracture at all temperatures except for S3. At 195 oC, the S3 extrudates which
were added with acrylic impact modifier fractured completely giving a low impact
strength. However, at 190 oC and below, S3 extrudates failed in a mix mode with some
hinge break and some complete fractured. This shows that between 180 oC and 190 oC,
241
the extrudates were in ductile to brittle transition. Therefore, the experimental error
for S3 was higher at these temperatures. The impact strength of S3 as shown in Table
6.6 is the highest compared to other extrudates due to the effectiveness of acrylic to
enhance the impact strength.
Table 6.5: Effect of processing temperatures on the fracture properties of unfilled and
filled extrudates
Tdie
(oC)
180
Complete Fractured Samples (no. of samples)
So
S3
S7
S9
S21
S37
7
3
7
7
7
-
185
7
5
7
7
7
-
190
7
3
7
7
7
7
195
7
7
7
7
7
7
Table 6.6: Effect of processing temperatures on the heat of fusion and impact strength
of unfilled extrudates
Tdie.
(oC)
Heat of
Fusion
(J/g)
Impact
Strength
(kJ/m2)
So
4.7+0.7
Heat of
Fusion
(J/g)
Impact
Strength
(kJ/m2)
Impact
Strength
(kJ/m2)
Heat of
Fusion
(J/g)
S7
4.15
S3
82.2+40.1
2.68
15.5+1.6
180
2.23
185
2.53
5.4+0.4
5.81
48.2+43.5
2.93
7.7+3.9
190
2.82
5.3+0.5
5.49
63.1+37.3
4.72
9.3+1.2
195
5.71
4.8+0.6
5.93
15.8+2.1
4.82
9.7+2.4
Table 6.6 shows the effect of processing temperatures on the impact strength
of extrudates. The impact strength of S0 remained relatively constant as the
temperature increased from 180 oC to 195 oC, even though the heat of fusion at 195
o
C significantly increased to 5.71 J/g. It shows that these processing temperatures did
not affect the impact strength of this extrudate.
242
For S3, there were mixtures in the failure more for the samples at 180 oC, 185
o
C and 190 oC. Therefore, the impact strength of S3 at these temperatures was
fluctuated. Meanwhile, the impact strength of S3 dropped drastically as the
temperature increased from 190 oC to 195 oC. It seems not to be in consistent with
previous report. It was previously reported that the effectiveness of acrylic to enhance
the impact strength of PVC was independent of processing temperatures when
conducted at 175 oC, 180 oC, 185 oC and 190 oC (Robinovic, 1983). This is because
the dispersed rubber particles maintained their particle morphology in the continuous
PVC phase. Therefore, the high heat of fusion is the plausible factor that contributed
to the reduction of impact strength at 195 oC. Summers (1982) reported that as the
fusion level (heat of fusion) increased, the network structure related to the primary
particles dispersed progressively, leading to the reduction of PVC free volume. It
means that even though the crystallites formed from the recrystallization ties of
primary particles to form a stronger network structure, which subsequently improves
the toughness of PVC, the reduction of free volume nullify the contribution from the
formation of crystallites. Therefore, the reduction in free volume probably was the
overriding factor that resulted in the impact strength decreased as the processing
temperature was increased from 190 oC to 195 oC. Similar observations have also
been reported by other researchers (Cora et al., 1999). Based on the impact strength
value, the optimum processing temperature of S3 was 180 oC.
The impact strength of S7 dropped drastically as the processing temperature
increased from 180 oC to 185 oC and remained relatively constant as the processing
temperature increased from 185 oC to 195 oC. This indicates that the highest impact
strength of S7 occurred at 180 oC with heat fusion of 2.68 J/g. CPE morphologies in
the PVC melt was reported to be dependent on processing temperatures (Lutz, 1993).
This was due to its inherent solubility in the PVC, in which CPE tends to act as a
plasticizer rather than impact modifier as the temperature increased. Furthermore, at
higher processing temperature, the rubbery networks of CPE started to collapse. Also,
at higher processing temperature, primary particles of PVC fused completely and
resulted in the toughness of PVC extrudates to decrease.
243
Table 6.7 shows the effect of processing temperatures on the impact strength
and heat of fusion of filled PVC-U extrudates. The impact strength for S9, S21 and S37
was remained relatively constant as the temperature increased. However, the heat of
fusions generated by S9, S21 and S27 were different where S9 has the highest heat
fusion at all processing temperatures followed by S21 and S9. It indicates that the
addition of 9 phr acrylic contributed to the higher heat of fusion which resulted in the
higher impact strength compared to S9 and S37 at all processing temperatures. The
dissimilar observation on the effect of impact modifier on the impact strength and
heat of fusion can be seen at S37 extrudates. Even though heat of fusion of S37 (6.92
J/g) was slightly lower than S9 (7.73 J/g) at 195 oC, the impact strength of S37 was
greater than S9. It shows that the primary particles left in S37 and the presence of CPE
were able to maintain the good impact strength of this extrudate. On the other hand,
the primary particles of S9 underwent more fusion process, which was indicated by its
higher heat of fusion, and without impact modifier were unable to increase the impact
strength of extrudate (S9).
Table 6.7: Effect of processing temperatures on the heat of fusion and impact
strength of filled extrudates
Impact
Strength
(kJ/m2)
Impact
strength
(kJ/m2)
Impact
strength
(kJ/m2)
Tdie.
(oC)
Heat of
Fusion
(J/g)
180
1.91
S9
4.4+0.3
4.52
S21
6.2+0.4
-
-
185
4.49
4.7+0.5
8.02
6.6+1.1
-
-
190
4.72
4.6+0.4
9.05
6.0+1.1
4.89
4.9+0.6
195
7.73
4.4+0.4
9.38
5.8+0.7
6.92
5.5+0.6
Heat of
fusion
(J/g)
Heat of
fusion
(J/g)
S37
Even though S9, S21, and S37 have higher values of heat of fusion compared to
the unfilled PVC-U extrudates (S0 and S3), their impact strength was lower than S0
and S3. This is because of the influence of EFB fillers was significant in decreasing
the impact strength of filled PVC-U extrudates than fusion level.
244
6.3.3.2 Effect of Screw Speed
Table 6.8 shows the influence of screw speeds on the impact-fractured
extrudates. The results show that all extrudates underwent complete fracture at all
screw speeds except for S3. As reported in Chapter 3 (Section 3.3.2.1), the
effectiveness of acrylic impact modifier in enhancing the impact strength of PVC
compared to CPE was also shown in this study. The effect of screw speeds on the
impact strength of extrudates is shown in the Tables 6.9.
Table 6.8: Effect of screw speeds on the fracture properties of unfilled and filled
extrudates
Complete Fractured Samples (no. of sample)
S7
S9
S3
5
7
7
Screw
speed (rpm)
50
So
7
60
7
4
7
7
7
70
7
0
7
7
7
S21
7
Table 6.9: Effect of screw speeds on the impact strength of unfilled and filled
extrudates
S0
4.5+0.9
Impact Strength
(kJ/m2)
S3
S7
S9
80.8+30.3
15.9+1.1
4.9+0.3
S21
5.7+0.5
60
4.7+0.7
82.2+40.1
15.5+1.6
4.4+0.3
6.2+0.4
70
5.4+0.7
93.6+13.9
12.9+1.1
3.6+0.5
6.2+1.0
Screw
speed
(rpm)
50
Table 6.9 shows that the impact strength of all extrudates was relatively
constant as the screw speed increased from 50 to 70 rpm, except for S7 and S9. It
implies that the increase of shear rate (screw speed), which contributed to the increase
245
of fusion level, did not affect the impact strength of extrudates. Table 6.9 also shows
that the impact strength of S3 was the highest compared to the rest of extrudates. It
elucidates that S3 appeared to be more susceptible to fuse due to the presence of
acrylic impact modifier when the rate of shear increased. It may be the fusion level of
S3 progressively increased as the screw speed increased. Previous studies on PVC
have shown that the impact strength increased with increasing fusion level. Marshall
et al. (1983) reported that the increase of fusion level with the influence of screw
speed was able to improve the impact strength of PVC. Covas and Gilbert (1992) also
reported that although the temperature was the main effect, increasing screw speed
also produced a significant jump in the level of fusion.
The decreasing in impact strength of S7 may be due to the network structure of
CPE to enclose primary particles that formed during the fusion process was destroyed
as the screw speed increased from 60 to 70 rpm. CPE became distributed as droplets
within a continuous PVC-U phase at higher shear rate (Mac Gill and Wittstock, 1987).
In this case, CPE was unable to form strong ties between primary particles in order to
improve the PVC toughness.
Table 6.9 also shows that the impact strength of S9 decreased with increasing
screw speeds. This was due to the EFB fillers poorly dispersed in the PVC-U matrix
as the residence time decreased (Table 6.2). It indicates that the increase of shear rate
to impart a good toughness through the increase of fusion level of S9 was inhibited by
the agglomeration of fillers, which contributed to the reduction in impact strength of
S9. It means that impact strength was more influenced by fusion level at lower screw
speed, whereas fillers agglomeration was predominated at higher screw speed in
decreasing the toughness. The addition of the acrylic in S21 was able to compensate
the agglomeration of filler effect and improved the impact strength of filled extrudates.
The impact strength of S21 remained constant as the screw speed increased from 50
to70 rpm.
246
6.3.4 Flexural Properties
6.3.4.1 Effect of Processing Temperature
Tables 6.10 and 6.11 show the effects of processing temperatures and heat of
fusion on the flexural modulus of extrudates. The flexural modulus of S0, S9 and S21
was relatively constant as the processing temperature increased from 180 oC to 195 oC.
It shows that the stiffness of S0, S9 and S21 was insignificantly affected by the increase
of processing temperatures and heat of fusion. Table 6.10 and 6.11 also show that the
flexural modulus of S3, S7 and S37 was only significantly increased at 195 0C. The
primary particles dispersion of these extrudates progressively increased at 195 oC due
to the increase of heat of fusion was probably attributed to the increase of stiffness.
Table 6.10: Effect of processing temperatures on the flexural modulus of unfilled
extrudates
Tdie.
(oC)
Heat of
fusion
(J/g)
Flexural
Modulus
(MPa)
So
Heat of
fusion
(J/g)
Flexural
Modulus
(MPa)
Heat of
fusion
(J/g)
Flexural
Modulus
(MPa)
S7
S3
180
2.23
3486+23
4.15
2824+124
2.68
2792+126
185
2.53
3439+86
5.81
2892+115
2.93
2586+156
190
2.82
3363+160
5.49
2821+147
4.72
2781+164
195
5.71
3568+234
5.93
3088+81
4.82
2896+45
247
Table 6.11: Effect of processing temperatures on the flexural modulus of filled
extrudates
Tdie.
(oC)
Heat of
fusion
(J/g)
Flexural
Modulus
(MPa)
Flexural
Modulus
(MPa)
Heat of
fusion
(J/g)
S21
S9
Flexural
Modulus
(MPa)
Heat of
fusion
(J/g)
S37
180
1.91
3514+147
4.52
3051+63
-
-
185
4.49
3609+133
8.02
2937+89
-
-
190
4.72
3579+79
9.05
2926+121
4.89
2443+219
195
7.73
3613+16
9.38
2980+101
6.92
2797+157
The effect of extrusion processing temperatures on the flexural strength for all
extrudates is shown in Table 6.12.
The flexural strength for all extrudates was
relatively constant as the temperature increased from 180 oC to 195 oC. It shows that
the flexural strength of all extrudates was not affected by the processing temperatures
and the progressive fusion of primary particles of the PVC.
Table 6.12: Effect of processing temperatures on the flexural strength of unfilled and
filled extrudates
Tdie.
(oC)
Flexural Strength (MPa)
S0
S3
S7
S9
S21
S27
180
90+2
69+1
68+2
76+3
61+2
-
185
86+4
67+2
64+4
76+2
60+1
-
190
82+4
66+1
65+2
75+1
60+1
55+4
195
88+4
67+2
65+3
73+2
59+2
57+2
248
As discussed in Chapter 3 (Section 3.3.2.2), Tables 6.10, 6.11 and 6.12 show
that the addition of impact modifier in PVC-U reduced the flexural modulus and
strength of S3 and S7. However, the results show that the modulus and strength of S3
were higher than S7 at all processing temperatures. This is due to CPE has more
softening effect than acrylic in reducing the rigidity of PVC. The similar reason can
also be used to elucidate the higher modulus and strength of filled extrudate, S21
compared to S37.
The incorporation of EFB fillers in the filled extrudates resulted in the
modulus of S21 was higher than unfilled extrudate (S3) at all temperatures, except at
195 oC. On the other hand, the flexural strength of S21 was lower than S3 for all
temperatures. The combination effects such as poor distribution of EFB fillers and
increment of heat of fusion were plausible factors for the slightly lower of modulus (at
195 oC) and strength of S21 (all processing temperatures) compared to S3. These
factors can also be used as reasons to elucidate the lower modulus and strength of S37
compared to S7.
6.3.4.2 Effect of Screw Speed
Tables 6.13 and 6.14 show the effect of screw speeds on the flexural
properties of unfilled and filled extrudates. The flexural modulus and strength of S0
increased as the screw speed was increased from 50 to 60 rpm. As the screw speed
further increased to 70 rpm, the modulus and strength remained relatively constant.
The results indicate that in general the flexural modulus and strength of extrudates
were not significantly affected by the screw speed. Extrudate, S0 was the most
affected by the screw speed with 5 % and 8 % increment in modulus and strength,
respectively, as the screw speed increased from 50 to 60 rpm.
249
Table 6.13: Effect of screw speeds on the flexural modulus of unfilled and filled
extrudates
Screw
Flexural Modulus (MPa)
Speed
S0
S3
50
3309+133
2794+296
2685+93
3344+115
3066+97
60
3486+23
2824+124
2792+126
3514+147
3051+63
70
3426+97
2652+77
2621+191
3242+198
2918+127
(rpm)
S7
S9
S21
Table 6.14: Effect of screw speeds on the flexural strength of unfilled and filled
extrudates
Flexural Strength (MPa)
Screw
Speed
S0
S3
S7
S9
S21
50
83+5
68+4
66+4
74+2
61+2
60
90+2
69+1
68+2
76+3
61+2
70
88+2
65+1
65+3
75+2
59+2
(rpm)
6.3.5 Tensile Properties
Tensile test was done to determine the yield stress and strain at break of
extrudates at difference screw speeds and processing temperatures. The crosshead
speed used was fixed at 20 mm/min.
Tables 6.15 and 6.16 show that the yield stress of extrudates increased as the
temperature increased from 180 to 185 oC and remained relatively constant as the
250
temperature increased to 195 oC. Table 6.17 shows that the yield stress values of the
extrudates were also not significantly affected by the increase of screw speeds. The
tensile test has indicated that yield stress was not sensitive to the variation of screw
speeds whereas slightly influenced by the processing temperature especially below
185 oC. Similar observations have also been reported by Benjamin (1980) and Truss
(1985) for unmodified PVC specimens from the wall of pipes extruded at difference
temperatures. The tensile stress increased gradually with increasing fusion level to
reach a maximum value and thereafter remained constant. Because of the yield stress
was only marginally changed, they concluded that the yield stress was relatively
independent to the processing temperature. Therefore, the yield stress obtained in this
study can also be said to be relatively independent to the fusion level. The research
works done by Terselius and Jasson (1984), and Patel and Gilbert (1985) also showed
the similar results.
The insensitivity of the yield stress on the fusion level is a fact, which is of
considerable relevance to the discussion of molecular deformation mechanism at
yielding. Since the increase of fusion level was associated with the increase of the
strength and coherence of the entanglement network (Terselius and Jansson, 1985),
yielding evidently involved molecular arrangements between entanglement and
network junctions. The fact that the yield stress was independent of the molecular
weight was a further support (Terselius and Jansson, 1984).
Table 6.15: Effect of processing temperatures on the yield stress of unfilled
extrudates at screw speed of 60 rpm
Tdie.
(oC)
Yield
Stress
(MPa)
Heat of
Fusion
(J/g)
Yield
Stress
(MPa)
Heat of
Fusion
(J/g)
So
Yield
Stress
(MPa)
Heat of
Fusion
(J/g)
S7
S3
180
2.23
43.8 + 2.0
4.15
42.1 + 1.4
2.68
41.0 + 1.7
185
2.53
55.4 + 2.1
5.81
44.1 + 0.5
2.93
42.7 + 3.9
190
2.82
57.6 + 1.6
5.49
47.3 + 1.8
4.72
42.2 + 2.7
195
5.71
55.7 + 3.4
5.93
47.3 + 1.5
4.82
44.5 + 1.0
251
Table 6.16 : Effect of processing temperature on the yield stress of filled extrudates at
screw speed of 60 rpm
Tdie.
(oC)
Heat of
Fusion
(J/g)
Yield
Stress
(MPa)
Heat of
Fusion
(J/g)
Yield
Stress
(MPa)
Heat of
Fusion
(J/g)
S21
S9
Yield
Stress
(MPa)
S37
180
1.91
40.9 + 1.0
4.52
34.3 + 1.4
-
-
185
4.49
49.8 + 1.9
8.02
39.8 + 0.7
-
-
190
4.72
48.9 + 1.0
9.05
38.9 + 0.4
4.89
32.9+2.5
195
7.73
47.7 + 1.1
9.38
38.9 + 0.9
6.92
33.5+3.5
Table 6.17: Effect of screw speeds on the yield stress of extrudates at die temperature
of 180 oC
Speed
(rpm)
50
S0
43.0 + 3.7
Yield Stress (MPa)
S9
S3
S7
38.9 + 1.4
43.2 + 1.2 41.6 + 2.5
S21
31.7 + 1.4
60
43.8 + 2.3
40.9 + 1.3
42.1 + 1.4
41.5 + 0.4
34.3 + 1.6
70
43.8 + 2.7
40.4 + 2.9
44.3 + 1.8
43.4 + 2.0
32.9 + 2.6
Tables 6.15-6.17 also show that the yield stress of S3, S7, S9 and S21 were
lower than S0. It shows that the impact modifier and EFB filler were able to reduce
the yield stress of PVC for yielding process to occur. The ability of impact modifier to
reduce the yield stress and facilitate the cold drawing, which resulted in the increase
of energy absorption of PVC, has also been reported by other researchers (Petrich,
1973; Marshall, 1982; Stevenson, 1995). The impact modifier provided sites of stress
concentration that occurred in the PVC matrix around an impact modifier particle
upon application of the tensile stress to the material. Since these localized
concentrations were well dispersed throughout PVC-U matrix, the shear yielding of
impact-modified extrudates was initiated easily upon tensile (Figure 6.7).
252
The reason EFB filler reduced the yield stress of PVC can be explained by the
increase in numbers of voids, which acted as stress concentration sites for yielding to
be initiated more easily (Nakamura et al., 1998; Liang et al., 2000). Unlike impact
modifier (rubbery particles), fillers did not deform as the external stress was applied
to specimen because the modulus of fillers are usually greater than that of the matrix.
When the applied stress exceeded the interfacial adhesion strength between EFB and
PVC, debonding at the interfaces would occur first, leading to the formation of microvoids. In this case, the deformation restraint of the matrix around the filler was
released, resulting in the shear yielding (shear yielding was favored than crazing due
to weak interfacial bonding) and absorbed strain energy of PVC without blocking the
propagation of cracks (Liang et al., 2000). Although the voids were able to provide
stress concentrations to facilitate the shear yielding, they were not as effective as the
impact modifier (Figure 6.7). Besides that, the voids also act as a defect, which can be
seen in the broken specimens. Because of the presence of voids, the reduction of yield
stresses of filled extrudates was slightly higher than unfilled extrudates. The yield
stresses of filled extrudates (S21 and S37) were further reduced when the impact
modifier was added into the filled extrudates.
The strain at break, which indicates ductility of the materials, is shown in
Tables 6.18-6.20. It can be seen that in general the strain at break of extrudates was
not significantly affected by screw speed and processing temperature except for S3.
As mentioned earlier in the impact strength section, the decrease of the strain at break
of S3 was due to the reduction of free volume of PVC. Tables 6.18-6.20 also show that
the trend of the strain at break values was similar to the trend showed by the impact
strength values in Tables 6.6, 6.7 and 6.9. This trend shows that the highest value of
strain at break occurs at the highest value of impact strength. In other words, the
results obtained in Tables 6.18-6.20 were well-correlated to the impact strength
results as shown in Tables 6.6, 6.7 and 6.9. Thus, the fusion level determined the
level of ductility of extrudates in terms of strain break. Therefore, the combination of
new network structures and some remaining primary particles in the extrudates
contributed to the strain at break.
253
S0
S3
S7
S9
S21
50
45
40
Stress (MPa)
35
30
S3 (117%)
25
20
15
10
5
0
0
2
4
6
8
10
12
14
16
18
20
Strain (%)
Figure 6.7 A typical stress-strain graph of tensile for extrudates at 60 rpm and 180 oC
Tables 6.19 and 6.20 show that the strain at break of filled extrudates was
lower than unfilled extrudates. The strain break reduction was attributed to the
detrimental effect of EFB fillers and the presence of voids in S9, S21 and S37. For
unfilled impact-modified extrudates, as expected, the addition of impact modifier in
the S3 ad S7 has promoted the PVC-U matrix to experience cold drawing after
yielding and thus, increasing the energy absorption (Figure 6.7). The ability of the
impact-modified PVC matrix to enhance the energy absorption by cold drawing
(plastic deformation) has also been discussed by other researchers (Bucknall, 1977,
Newman and Stella, 1965). A more applicable discussion to the behaviour of impactmodified PVC has been suggested by Newman and Stella (1965). They suggested that
the cold drawing of the glassy matrix resulted in the increase of free volume of the
matrix around rubbery particles, due to the resistance of the particles to change in
volume. The expansion of matrix surrounding the particle generated heat that increase
22
254
the temperature of the matrix, so that it approached its glass transition temperature
and deformed more easily and absorbed more energy in viscous flow process.
Table 6.18: Effect of processing temperature on the strain at break of unfilled
extrudates at screw speed of 60 rpm
Tdie.
(oC)
Heat of
Fusion
(J/g)
Strain at
Break
(%)
Heat of
Fusion
(J/g)
So
Strain at
Break
(%)
Heat of
Fusion
(J/g)
Strain at
Break
(%)
S7
S3
180
2.23
10.7 +5.1
4.15
132.1 + 65.4
2.68
38.4 + 3.0
185
2.53
19.3 + 5.0
5.81
103.4 + 77.9
2.93
21.1 + 9.6
190
2.82
15.1 + 1.7
5.49
62.5 + 57.3
4.72
19.4 + 5.4
195
5.71
6.9+ 0.7
5.93
29.2+10.5
4.82
20.7+2.0
Table 6.19: Effect of processing temperature on the strain at break of filled extrudates
at screw speed of 60 rpm
Tdie.
(oC)
Heat of
Fusion
(J/g)
Strain at
Break
(%)
Strain at
Break
(%)
Heat of
Fusion
(J/g)
S21
S9
Strain at
Break
(%)
Heat of
Fusion
(J/g)
S37
180
1.91
6.2 + 0.8
4.52
4.9 + 0.6
-
-
185
4.49
7.6 + 0.9
8.02
11.1 + 1.8
-
-
190
4.72
6.0 + 0.6
9.05
9.7 + 2.1
4.89
8.0 + 1.2
195
7.73
6.9+ 0.7
9.38
10.2+2.4
6.92
8.2 + 1.8
255
Table 6.20: Effect of screw speed on the strain at break at die temperature of 180 oC
Speed
(rpm)
50
S0
14.7 + 7.1
Strain at Break (%)
S3
S7
S9
99.7 + 65.4
23.5 + 5.7
6.9 + 1.3
S21
5.0 + 1.0
60
10.7 + 5.2
132.1 + 77.9
38.4 + 3.0
6.2 + 0.8
4.9 + 0.6
70
16.7 + 6.2
172.3 + 57.3
36.9 + 11.3
6.0 + 0.5
4.6 + 0.9
6.3.6 Yield Stress Analysis
In this section, the yield stress analysis was done to predict the yield stress of
the extrudates at an impact velocity of 3 m/s. This impact velocity was used for
pendulum impact testing. Extrudates produced at 180 oC and 190 oC with constant
screw speed of 60 rpm were chosen for this analysis.
A linear regression was
performed on the yield stress data at lower strain rate (Table 6.21) using the Eyring
equation of plastic yielding to obtain the yield stress at 3 m/s.
Table 6.21: Effect of strain rate on the yield stress of unfilled and filled extrudates
Crosshead
Strain
Strain
speed
rate
rate
(mm/min)
-1
(ln)
(s )
Yield stress ( MPa)
S0
180
o
S9
190
o
180
o
S3
190
o
180
o
S7
190
o
180
o
S21
190
o
180
o
190
o
S37
190
( C)
( C)
( C)
( C)
( C)
( C)
( C)
( C)
( C)
( C)
(oC)
5
0.001
-6.571
38.8
53.7
37.6
46.4
40.8
44.1
37.5
40.3
31.7
36.5
26.3
20
0.006
-5.185
43.8
57.6
40.9
48.9
42.1
47.3
41.0
42.2
34.3
38.9
26.9
80
0.022
-3.808
45.1
60.9
43.6
51.8
46.0
50.1
43.3
45.6
35.2
41.3
28.1
100
0.028
-3.583
45.2
61.7
44.1
52.2
46.6
49.3
42.8
46.2
37.2
41.7
29.0
The effect of strain rate on the yield stress of the extrudates is shown in Table
6.21. It shows that the yield stress increased as the strain rate increased. The yield
256
stress of S0 was higher than other extrudates at all strain rate. The increase of yield
stress as the strain rate increased was also found by Wee (2001). It indicates that the
yielding process being suppressed with the increase of strain rate, and thus the
fracture tended to change from ductile to brittle behaviour. It can be explained in
molecular aspect, where during yielding the molecular chains are uncoiled and slip
past each others and gradually align closer in the reaction of the tensile stress. As the
strain rate increased, the rate of extension molecular chains to align and stiff become
faster and then the stress on the molecular chains increased. Eventually, the covalent
bonds of the main chains break and fracture of the material occurred (Smith, 1996).
The Eyring equation has been previously used by other researchers (Calvert et
al.,1991; Azman Hassan,1996; Wee, 2001) in their studies to predict the yield stress
values of impact-modified PVC-U at high strain rate. The Eyring theory has described
that the yield behaviour of polymers to be dependent on the temperature and rate of
deformation. In the high stress region where yield occurs, the Eyring equation gives
the yield stress (σy) in terms of the strain rate at yield (ε) as :
σy
T
=
k ⎡ ln ε ∆H ⎤
+
γν ⎢⎣ A kT ⎥⎦
(6.1)
where, Α is a constant, ν is the activation volume, ∆H is a activation energy for the
low process, k is Boltzmann’s constant, γ is a stress concentration factor and T is an
absolute temperature. The plots of σy for all extrudates at temperature of 180 oC and
190 oC against natural log tensile strain rate were increased linearly as shown in
Figure 6.8. The equation obtained by linear regression and extrapolating was used to
predict the σy at constant testing temperature. The value of slope was represented for
value of k/γνA while the intercept was represented for value of ∆H/k. Thus, to
obtain σy, the strain rate at impact velocity was firstly determined.
257
100
y = 2.6301x + 71.064
2
Yield Stress (MPa)
R = 0.9984
190 oC
80
60
y = 2.2871x + 54.497
2
R = 0.8988
40
180 oC
20
0
-8.000
-6.000
-4.000
-2.000
0.000
2.000
4.000
Strain Rate (ln)
Figure 6.8
Predicted yield stress values at 3 m/s for S0
In order to determine the apparent strain rate of the impact test in three point
bending, both equations from the flexural strength and modulus were used and
rearranged using Hooke’s Law and resulting in the following equation:
ε=
6vd
L2
(6.2)
where v is the impact velocity, d is the mean thickness of the specimens of the
sample and L is the span between the centers of support. By substituting the relevant
data, the strain rate for impact velocity of 3 m/s was found to be 20.76 s-1. It was
substituted into the regression equation, which was obtained from the graph. The
predicted σy of extrudates at 3 m/s are shown in Table 6.22 and Table 6.23. From the
predicted yield stress, the incorporation of EFB filler and impact modifier decreased
the yield stress of the filled and impact-modified extrudates. The ability of EFB filler
and impact modifier in reducing the yield stress has previously discussed.
258
Table 6.22: Predicted yield stress of extrudates at 3 m/s, die temperature of 180 oC
and screw speed of 60 rpm
Extrudate
Equation
Predicted Yield Stress (MPa)
S0
σy =2.2871(ln ε) + 54.497
61.4
S9
σy =2.1534(ln ε) + 51.853
58.4
S3
σy =2.0092(ln ε) + 53.492
59.6
S7
σy =1.8543(ln ε)+ 50.026
55.6
S21
σy =1.5461(ln ε)+ 41.976
46.7
Table 6.23: Predicted yield stress of extrudates at 3 m/s, die temperature of 190 oC
and screw speed of 60 rpm
Exrudate
Equation
Predicted Yield Stress (MPa)
S0
σy =2.6301(ln ε) + 71.064
79.0
S9
σy =1.9601(ln ε) + 59.208
65.1
S3
σy =1.8882(ln ε) + 56.738
62.5
S7
σy =2.0056(ln ε)+ 53.175
59.3
S21
σy =1.7393(ln ε)+ 47.926
53.2
S37
σy =0.8430(ln ε)+ 31.619
34.2
6.3.7 General Discussion
Table 6.24 shows the inter-relationship between impact strength, predicted
yield stress and strain at break of extrudates at die temperature 180 oC and 190 oC.
259
The results show that the yield stress of all extrudates increased as the temperature
increased. It is interesting to note the ability of S0 and S9 extrudates to increase in
strain at break and yield stress with the increase of temperature. This could be
attributed to the increase of fusion level thus increasing the number of effective
entanglement and crystalline junctions favouring orientation hardening.
Table 6.24: Impact strength, yield stress and strain at break at die temperature 180 oC
and 190 oC
180 oC
Sample
190 oC
S0
Impact
Strength
(kJ/m2)
4.7
Yield
Stress
(MPa)
61.4
Strain at
Break
(%)
11
Impact
Strength
(kJ/m2)
5.3
Yield
Stress
(MPa)
79.0
Strain at
Break
(%)
15
S3
82.2
59.6
132
63.1
62.5
63
S7
15.5
55.6
38
9.3
59.3
19
S9
4.4
58.4
6
4.6
65.2
6
S21
6.2
46.7
5
6.0
53.2
10
Table 6.24 also shows the impact strength and strain at break of impactmodified extrudates (S3 and S7) decreased while the yield stress increased as the
temperature increased. The increase of yield stress of S3 and S7 was attributed to the
increase of fusion level of PVC, while the decrease of impact strength and strain at
breaks was attributed to the increase of miscibility of acrylic and CPE in the PVC.
This could be a reason why the strain at break and the impact strength decreased at
higher temperature. Wimolmala et al. (2001) also reported that at higher temperature
(195 oC) the PVC became more miscible with the acrylic rubber and resulted in the
decrease of tensile toughness. Similar to the excessive increases of impact modifier
concentration, the excessive increases of temperature can produce lower impact
strength of PVC.
260
In terms of relationship between fusion level and mechanical properties, as
reported previously, the highest impact strength and strain at break of S0, S3, S9 and
S21 occurred at temperature of 185 oC with heat of fusion of 2.53 J/g, 4.15 J/g, 4.49
J/g, and 8.02 J/g, respectively. For S7 and S37, the highest impact strength and strain at
break occurred at temperature 180 oCand 195 oC. The heat of fusion of S7 and S37
was 2.68 J/g and 6.92 J/g, respectively. The occurrence of the highest impact strength
and strain at break at the moderate fusion level as found in this study was in
agreement with the other researchers (Benjamin, 1980; Uitenham and Geil, 1981;
Terselius and Jansson, 1981, 1984, 1985). The flexural properties and yield stress
were found insensitive to the increase of fusion level, which contributed by the
increase of temperature and screw speed.
6.4
Conclusions
The mechanical properties and fusion analysis of extrudates were studied.
Based on the results obtained several conclusions can be made:
(a)
The filled extrudates incorporated with 10 phr of filler can be extruded with a
smooth surface. The rough surface of extrudates appeared after leaving the die
for the extrudates incorporated with 20 phr filler, due to fillers poor
distribution and dispersion in the matrix.
(b)
The filled compound (S37) containing 10 phr of EFB and 9 phr of CPE can
only be extruded at die temperatures of 190 oC and 195 oC. This extrudate
experienced melt fracture (melt bambooing) when extruded at below these
temperatures. The increase of melt viscosity due to the delaying of PVC fusion
resulted in the melt fracture of extrudates.
261
(c)
The heat of fusion of extrudates increased with increasing processing
temperature due to the increase of thermal energy. Similar to impact modifier,
EFB filler has ability to increase the fusion level of filled extrudates, due to
the increase of frictional heat, particularly when combined with acrylic impact
modifier.
(d)
The impact strength of all extrudates was relatively constant as the screw
speed increased from 50 to 70 rpm, except for S7 and S9. The influence of
screw speed on the flexural properties and yield stress of extrudates is not
significant.
(e)
The impact strength of S9, S21 and S37 relatively constant as the temperature
increased from 180 to 195 oC while the impact strength of S7 relatively
constant from 185 to 195 oC. The impact strength of S3 drastically decreased
as the temperature increased to 195 oC. The increase of temperature from 180
to 185 oC slightly increased the yield stress of extrudates. However, yield
stress remained relatively constant as the temperature increased from 185 to
195 oC. In most cases, the flexural properties and yield stress are independent
of processing temperatures.
(f)
The yield stress of extrudates is directly proportional to the strain rate of
tensile test. Similar to the experimental yield stress, the predicted yield stress
also increased with processing temperatures. Although the incorporation of
EFB reduced the yield stress of the PVC, the plastic deformation or strain
hardening of the extrudates filled with EFB during tensile testing was limited
(the inability of extrudates to elongate at higher value) . As a result, the impact
modified and unmodified filled extrudates (S9 and S21) has lower values of
strain at break and impact strength than the respective unfilled samples.
CHAPTER 7
OVERALL CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK
7.1
Conclusions
In this study, two processing methods were used to produce the PVC-U
composites samples; compression moulding and extrusion. EFB-filled PVC-U
composites with up to 40 phr filler content were produced using the compression
moulding i.e. using a two-roll mill and hot press (Chapter 3). For the extrusion, only
extrudates with 10 phr filler could be successfully produced (Chapter 6). The smooth
surface of extrudates changed to be rough as the filler content increased to 20 phr. It
shows that in single screw extrusion of EFB filled PVC-U composites, high L/D ratio
is required to ensure the dry blends have a sufficient residence time for good melt
homogeneity before leaving the die.
The use of EFB fibre as a reinforcement filler in the compression moulded
composites contributed to the enhancement of stiffness, but decreased the ductility,
flexural strength of the PVC-U composites (Chapter 3). The results have shown that
the addition of acrylic and CPE impact modifier improved the toughness but reduced
marginally the flexural properties of EFB-filled composites. The study revealed that
acrylic is a better impact modifier in improving toughness and cause a lesser decrease
263
in flexural properties of filled impact-modified composites compared to CPE. Besides
that, the impact strength and flexural properties of filled composites added with
acrylic impact modifier were also found to be more stable in the accelerated
weathering than CPE. It was therefore decided to use only acrylic impact modifier for
the studies of filler-surface treatment of EFB-filled acrylic-impact modified
composites. Filler-surface treatment has fairly improved the toughness, stiffness, and
strength of these composites when treated with coupling agents, and Prosil 9234
proved to be more effective compared to NZ 44 coupling agent. FTIR spectra and
SEM micrograph showed that both coupling agents reacted with PVC to form
chemical interactions and simultaneously reduced water absorption of the coupling
agent-treated filled composites.
The effect of EFB filler on the thermal properties is another important area
which was investigated (Chapter 4). It was found that EFB filler marginally increased
the Tg and insignificantly changed the HDT. EFB filler, however, decreased
significantly the thermal stability of PVC. The addition of acrylic impact modifier has
also contributed to the further declining of the thermal stability of PVC. Although the
EFB-filled acrylic-impact modified composites have low thermal stability, these
composites have good processability characteristics compared to other composites
(Chapter 5).
The study in Chapter 6 has shown that it is possible to extrude 10 phr EFB
filled PVC-U composites at moderate temperatures (180-185 0C) and screw speeds
(50-60 rpm) for the unmodified and acrylic impact modified formulations. In the
extrusion, temperatures and screw speed governed the fusion level of PVC as
indicated by DSC analysis. The correlation between mechanical properties and fusion
level showed that the moderate fusion level contributed to the relatively better
mechanical properties. Although the temperature and screw speed are important
parameters governing extrusion process, the role of additives in the PVC-U compound
is also important. Therefore, it is anticipated that filled-impact modified extrudates
with 20 phr and higher can be extruded provided correlations between temperature,
screw speed, and other additives are thoroughly studied. Overall, it can be concluded
264
that EFB, which is agricultural by-product from oil palm trees, has the potential to be
used as filler in PVC composites as it enhanced the stiffness and reduced the cost of
the composites.
7.2
Suggestions for Future Work
From the present study, the following areas of research are needed for future
investigations:
(1)
Microstructure of the interface between EFB fibre and matrix still needs to be
investigated and the interfacial properties should be studied with more rigorous
single fibre pullout tests. The reason for this suggestion is to study in depth the
relationship between interface and untreated or between interface and treated
fibre surface composite properties. This suggestion can also be used to evaluate
the significance of using coupling agents in EFB fibre-filled PVC-U
composites.
(2)
In the study of the fibre-surface treatment of composites, the results have shown
that the improvement in mechanical properties is not encouraging. It would be
interesting to find out a more suitable coupling agent for the studied composites.
(3)
In the FTIR analysis, it is very difficult to distinguish clearly the nature of new
peaks observed for the treated composites. These peaks could be also the results
of the interaction between other additives and fillers or PVC and fillers, since
the formulation of PVC-U used in this study contained many additives. Further
research is needed to identify the role of each additive on the adhesion between
PVC and coupling agent-treated EFB filler.
265
(4)
In extrusion, the amount of processing aid content in the blend formulations was
kept constant at 1.5 phr. Thus, in order to overcome the difficulty to extrude the
extrudates filled containing 20 phr and higher, a possible method can be
investigated to increase the processing aid content in the blend formulations.
This should be investigated. Besides that, the L/D of screw and type of extruder
also play an important role in determining the efficiency of mixing of the
blends, thus influencing the quality of filled extrudates. Therefore, the other
possible methods need for further investigations, which can be used to
overcome the problem of extrudate filled with 20 phr and higher, are to use a
higher L/D ratio or twin screw extruder in order to increase the efficiency of
mixing and avoid the thermal degradation.
(5)
New application should be found for EFB-fibre-based composites. Hybrid fibre
composites with EFB fibre and other fibres rather than glass may open up new
applications. For example, from the economics point of view, EFB fibres may
be hybridised with carbon or aramid fibres to reduce the costs of these
expensive fibres reinforced composites whilst maintaining their good
mechanical performance.
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