Document 14602910

BAHAGIAN A – Pengesahan Kerjasama*

Adalah disahkan bahawa projek penyelidikan tesis ini telah dilaksanakan melalui kerjasama antara ________________________ dengan ______________________

Disahkan oleh:

Tandatangan : ………………………………………………..

Nama

Jawatan

(Cop rasmi)

: ………………………………………………..

: ………………………………………………..

Tarikh : ………….

* Jika penyediaan tesis/projek melibatkan kerjasama.

BAHAGIAN B – Untuk Kegunaan Pejabat Sekolah Pengajian Siswazah

Tesis ini telah diperiksa dan diakui oleh:

Nama dan Alamat : Prof. Dr. Rozman Bin Hj. Din

Pemeriksa Luar Pusat Pengajian Teknologi Industri

Universiti Sains Malaysia

11800 MINDEN

Pulau Pinang

Nama dan Alamat : Prof. Madya Dr. Wan Aizan Binti Wan Abd Rahman

Pemeriksa Dalam I Fakulti Kejuruteraan Kimia & Kejuruteraan Sumber Asli

UTM, Skudai

Pemeriksa Dalam II :

Nama Penyelia Lain :

(jika ada)

Disahkan oleh Penolong Pendaftar di Sekolah Pengajian Siswazah:

:

Tandatangan : ………………………………………… Tarikh : ……….……….

Nama : GANESAN A/L ANDIMUTHU

MECHANICAL PROPERTIES OF RICE HUSK FILLED IMPACT MODIFIED

UNPLASTICISED POLY(VINYL CHLORIDE) COMPOSITE

MAZATUSZIHA BINTI AHMAD

A thesis submitted in fulfilment of the requirements for the award of the degree of

Master of Engineering (Polymer)

Faculty of Chemical and Natural Resources Engineering

Universiti Teknologi Malaysia

JANUARY 2006

‘Specially for my beloved parents’ iii

iv

ACKNOWLEDGEMENT

First and foremost I would like to offer my unreserved gratitude and praises to

Almighty Allah for His generous blessing and the undying strength bestowed upon me during the course of this research.

The constant encouragement and guidance offered by Dr. Abdul Razak Rahmat,

Associates Prof. Dr. Azman Hassan and Dr. Kairul Zaman under whose supervision the work described here was carried out are gratefully acknowledged.

My special appreciation goes to En. Aznizam Abu Bakar who willingly spared his time in helping me on the thesis writing and sample preparations works. I also wish to thank all my friends Su, Kak Nun, Yani, Lim, Fara, Suhaimi, Chen and En Mat Uzir for their continuous support and help especially in periods of uncertainties and difficulties. Also my gratitude to all the technicians and lab assistant of Polymer

Engineering Laboratory, for their help in performing the tests.

I am gratefully acknowledged to IRPA, Malaysia Vote 74126 for the generous financial and providing me scholarship to carry out the study.

Last but not least I wish my appreciation and thanks to my beloved parents and sister for their endless patience, love and encouragement shown throughout the entire research period. Thank you.

v

ABSTRACT

Rice husk (RH) is one of the natural fillers that offer a number of advantages over inorganic fillers since they are biodegradable, low cost, recyclable and renewable.

This study investigates the performance of RH as filler for unplasticised poly(vinyl chloride) (PVC-U) composites. In the sample preparation, composites with different RH loadings varied from 10 to 40 phr were prepared using two-roll mill at temperature 165 o C before being hot pressed at temperature 185 o C. Tensile, flexural and izod impact test were conducted in order to investigate the mechanical properties of the composites.

Incorporation of RH fillers from 10 to 40 phr has resulted in the increased of flexural modulus indicating an improvement in stiffness. The effects of acrylic impact modifier and LICA 12 coupling agent on the mechanical properties of PVC-U composites were investigated. The acrylic impact modifiers were found to be effective in enhancing the impact strength at all levels of RH content. Effectiveness of the impact modifier in enhancing the impact strength decreased with increasing RH content. LICA 12 was found to be the most effective in increasing impact strength at 20 phr RH loading. The processability of RH filled PVC-U composites was studied by using Brabender

Plasticorder. It was found that incorporation of RH has resulted in decreasing the fusion time of the PVC compounds while the heat distortion temperature (HDT) increased at all RH loadings. The degradation temperature (T

10%

) decreased with increasing RH content. The percentage of water absorption increased slightly with increasing RH content and treated samples exhibited lower percentage of water absorption compared to the untreated samples. The optimum composition which gives balance of properties based on stiffness and toughness of PVC-U composites is PVC-U at 8 phr of acrylic impact modifier and 20 phr of RH treated with LICA 12.

vi

ABSTRAK

Sekam padi merupakan pengisi semulajadi yang mempunyai banyak kelebihan berbanding pengisi tidak organik kerana ia boleh terbiodegradasi, mempunyai kos yang rendah, boleh dikitar semula dan merupakan bahan semulajadi. Penyelidikan ini mengkaji kebolehan sekam padi sebagai pengisi alternatif terhadap komposit pol(ivinil klorida) tidak terplastik (PVC-U). Dalam penyediaan sampel, komposit dengan kandungan sekam padi dari 10 hingga 40 phr disediakan menggunakan penggiling dua pada suhu 165 o C sebelum pengacuan mampatan dilakukan pada suhu 185 o C. Ujian regangan, lenturan dan hentaman Izod dilakukan untuk mengkaji sifat-sifat mekanikal komposit. Kajian menunjukkan, penambahan sekam padi dari 10 hingga 40 phr meningkatkan modulus lenturan disebabkan kekakuan bahan meningkat. Kesan pengubahsuai hentaman akrilik dan agen perekatan LICA 12 terhadap sifat-sifat mekanikal komposit PVC-U dikaji. Pengubahsuai hentaman akrilik didapati berkesan meningkatkan kekuatan hentaman pada setiap kandungan sekam padi. Keberkesanan pengubahsuai hentaman dalam meningkatkan kekuatan hentaman menurun dengan peningkatan kandungan sekam padi. LICA 12 amat berkesan meningkatkan kekuatan hentaman pada kandungan sekam padi 20 phr. Kebolehprosesan komposit berpengisi sekam padi dikaji menggunakan Brabender Plasticorder. Penambahan sekam padi didapati menyebabkan penurunan masa peleburan manakala suhu pembengkokkan haba

(HDT) meningkat pada setiap kandungan sekam padi. Suhu degradasi komposit menurun dengan peningkatan kandungan sekam padi. Peratus penyerapan air meningkat sedikit dengan peningkatan kandungan sekam padi dan sampel terawat LICA 12 menunjukkan peratusan yang rendah berbanding sample tidak terawat. Formulasi optimum yang memberikan kombinasi kekuatan hentaman dan kekakuan yang seimbang adalah komposit yang mengandungi 8 phr pengubahsuai hentaman akrilik dan

20 phr sekam padi yang dirawat dengan LICA 12.

vii

TABLE OF CONTENT

DEDICATION iii

ABSTRAK vi

LIST OF FIGURES

LIST OF ABREVIATIONS AND SYMBOLS

xiv xix

1 INTRODUCTION 1

Objectives Study 5

Significance 6

Scopes 7

REVIEW 8 viii

2.2.6

Thermal Stability of PVC

2.3 The Influence of Additives on PVC-U

17

20

2.3.3.1 Mechanism of Impact

Modification

26

2.4.1 Mechanism of Coupling Agent

2.5.1 Natural Fibers and Fillers:

Compositions and Properties

2.6 Rice Husk Filled Thermoplastic

Composites

2.7 Environmental Effects on Polymeric

Materials

2.8 Effect of Weathering on the PVC-U Composites

34

38

42

45

46

3 METHODOLOGY 50 ix

3.1.4 54

3.2 Testing Techniques

3.2.1 Impact

56

Flexural 57

3.2.4 Scanning Electron Microscopy

(SEM)

60

3.2.8 Heat Deflection Temperature

Testing

3.2.10 Fourier Transform Infra-Red (FTIR)

Spectroscopy

62

63

4 RESULTS AND DISCUSSION

4.1 Mechanical Properties of Rice Husk

Filled Impact Modified PVC-U Composites

63

63

4.1.1 The Effect of RH Content on Flexural

Properties of RH Filled Unmodified PVC-U

4.1.2 Effect of Acrylic Impact Modifier

Content on Impact Strength of Unfilled and RH Filled PVC-U


Content on Flexural Properties and of Unfilled and RH Filled PVC-U

4.1.4 Effect of RH Content on Impact

Strength of Unmodified and Impact

Modified PVC-U

4.1.5 Effect of RH Content on

Flexural Properties of Unmodified and Impact Modified PVC-U


Content on Tensile Properties of Unfilled and RH Filled PVC-U

4.1.7 Effect of RH Content on Tensile

Properties of Unmodified and Impact

Modified PVC-U

4.2 Effect of Weathering on Mechanical Properties of

Rice Husk Filled Impact Modified PVC-U Composites

4.2.1 Effect of Weathering on

Flexural Properties of RH Filled

Impact Modified PVC-U


Impact Strength of RH Filled



Tensile Properties of RH Filled


64

66

69

72

74

79

81

84

84

87

89 x

4.3

4.2.4 Fourier Transform Infrared Spectroscopy

(FTIR) Analysis

Effect of Coupling Agent on

Mechanical Properties of RH Filled

Impact Modified PVC-U Samples

4.3.1 Effect of Coupling

Agent on Impact Strength of RH Filled

Impact Modified PVC-U Composites


Agent on Flexural Modulus and

Flexural Strength of RH Filled



Agent on Tensile Strength and

Young Modulus of RH Filled


4.4 Comparison on Mechanical Properties

Between Rice Husk and Rice Husk Ash

Filled Impact Modified PVC-U Composites

4.5 Scanning Electron Microscopy Analysis

4.6.1 Thermogravimetry (TGA) Analysis

4.6.2 Heat Deflection Temperature (HDT)

4.6.2.1 Effect of RH Content on

HDT of Impact Modified PVC-U

Composites

4.7.1 Effect of RH Content Upon Fusion

Characteristics of Unmodified PVC-U


Content Upon Fusion Characteristics of

95

97

99

101

106

111

116

116

118

119

91 xi

95

xii

Unfilled PVC-U

4.8 Water Absorption

4.8.1 Percentage of Water Absorption Upon

Impact Modified PVC-U with

Varying RH Content

4.8.2 Percentage of Water Absorption Upon

Treated RH Filled Impact Modified PVC-U

Samples with varying RH Content.

122

122

124

5 CONCLUSIONS 126

REFERENCES 129

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Typical

2.2 Typical

2.3 List

2.4 Typical

2.5

2.6

3.1

Chemical Constituents of Rice Husk Fillers

Lignin in Miscellaneous Plant Materials

Chemical Properties of Polyvinyl chloride Resin K-66

39

40

50

3.2

3.3

Additives

Blend Formulation 1

3.4 Blend

3.5 Blend 3

50

4.1 Relative Flexural Modulus Value of Composite to Polymer

4.2 Degradation Temperature of Components Obtained from

52

78

113

4.4

TG and DTG Curves

4.3 Fusion Characteristics of Unmodified PVC

Fusion Characteristics of Modified PVC Blends

120

121 xiii

xiv

LIST OF FIGURES

FIGURE NO. TITLE

2.1 Repeating Unit Structure of Vinyl Chloride

Monomer

2.2

2.3

Schematic Diagram of PVC Powder Morphology

The Microdomain Structure of PVC

2.4 Schematic Model for PVC Degradation

2.5 Core/shell Impact Modifiers

2.6 Stress-distribution in Polymer Matrix Surrounding a Rubbery Impact Modifier Particle

2.7 Bonding Mechanism of Titanate Coupling

Agent to RH Filler’s Surface

2.8 Mechanism of Filler Dispersion in Polymer

Matrix

PAGE

11

34

36

14

15

18

24

25

3.1

3.2

Chemical Structure of LICA 12 Coupling Agent

Specimen Dimension for Izod Testing

[ASTM D 256(A)]

3.3 Support Span Arrangement for Flexural Testing

[ASTM D 790]

3.4

4.1

Specimen Dimension for Tensile Test of RH Filled PVC-U

The Effect of RH Content on Flexural Modulus

54

56

57

58

64

4.2

4.3

The Effect of RH Content on Flexural Strength of RH Filled PVC-U

The Effect of RH Content on Flexural Modulus and Flexural Strength of RH Filled

PVC-U

4.4 The Effect of Acrylic Impact Modifier Content on

Impact Strength of Unfilled PVC-U

4.5 The Effect of Acrylic Impact Modifier Content on

4.6

Impact Strength of RH Filled PVC-U (20 phr)

The Effect of Acrylic Impact Modifier Content on

Flexural Modulus of Unfilled And RH Filled

4.7

4.8

PVC-U


Flexural Strength of Unfilled and RH Filled PVC-U

The Effect of RH Content on Impact Strength of

Unmodified and Impact Modified PVC-U

4.9

4.10

4.11

The Effect of RH Content on Flexural Modulus of


The Effect of RH Content on Flexural Strength of



Tensile Strength of Unfilled and RH Filled

4.12

4.13

PVC-U


Young Modulus of Unfilled and RH Filled

PVC-U

The Effect of RH Content on Tensile Strength of


4.14 The Effect of RH Content on Young Modulus of


4.15 The Effect of Accelerated Weathering on

68

68

70

80

81

83

85

71

73

75

78

80

65 xv

66

xvi

Flexural Modulus of RH Filled Impact Modified PVC-U


Flexural Strength of RH Filled Impact Modified PVC-U


Impact Strength of RH Filled Impact Modified PVC-U


Tensile Strength of RH Filled Impact Modified PVC-U


Young Modulus of RH Filled Impact Modified PVC-U

4.20 FTIR Spectra for PVC-U Composites Under

Accelerated Weathering Conditions

4.21 The Effect of Coupling Agent on Impact Strength of RH Filled Impact Modified PVC-U

4.22 The Effect of Coupling Agent on Flexural Modulus of RH Filled Impact Modified PVC-U

4.23 The Effect of Coupling Agent on Flexural Strength of RH Filled Impact Modified PVC-U

4.24 The Effect of Coupling Agent on the Tensile Strength of RH Filled Impact Modified PVC-U

4.25 The Effect of Coupling Agent on the Young Modulus of RH Filled Impact Modified PVC-U

4.26 Comparison on Impact Strength between

Rice Husk and Rice Husk Ash Filled


4.27 Comparison on Flexural Modulus between



4.28 Comparison on Flexural Strength between



4.29 Comparison on Tensile Strength between

103

104

105

99

101

102

96

97

98

86

88

90

91

94

xvii

4.32(c)

4.32(d)

4.33(a)

Rice Husk And Rice Husk Ash Filled


4.30 Comparison on Young Modulus between


4.31


SEM Micrograph of Impact Fracture Surfaces

4.32(a)

4.32(b) of Unfilled Unmodified PVC-U

SEM Micrograph of Impact Fracture Surfaces of RH Filled Impact Modified PVC-U Composites at 10 phr Filler Content




SEM Micrograph of Impact Fracture Surface of Unfilled Impact Modified PVC-U Composites at 8 phr Impact Modifier Loading

4.33(b) SEM Micrograph of Impact Fracture Surface of Unfilled Impact Modified PVC-U Composites at 12 phr Impact Modifier Loading

4.34 TG Curves for PVC Powder, PVC-U Compound and RH Filler

4.35 DTG Curves for PVC Powder, PVC-U Compound and RH Filler

4.36 TG Curves for RH Filled PVC-U Composites

4.37 DTG Curves for RH Filled PVC-U Composites

105

106

107

108

108

109

110

110

112

112

115

116

4.38

4.39

Effect of RH Content on Heat Deflection

Temperature of Impact Modified

PVC-U Composites

Typical Temperature Torque Curves of RH Filled

PVC Compounds Blended in a Haake

Torque Rheometer

(starting temperature = 185 o C, rotor speed = 60 rpm)

4.40 Effect of Water Absorption Upon Impact Modified

PVC-U with Varying RH Content

4.41 Effect of Coupling Agent on Water Absorption Upon


PVC-U with Coupling Agent xviii

117

118

122

124

A

ABS

APE

ASTM d

DSC

DTG

EFB

EVA b

B

BRHA

CaCO

3

CO

2

CPE

FTIR

G f

G p

HCl

HDPE

HDT

H

2

O

KBr

L

LIST OF ABBREVIATIONS AND SYMBOLS

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Constant related to the Einstein coefficient

Acrylonitrile butadiene styrene

Aminopropyl triethoxysilane

American Standard of Testing Materials

Mean width of the specimens (m)

Related to the relative modulus of filler and polymer,

Black rice husk ash

Calcium carbonate

Carbon dioxide

Chlorinated polyethylene

Mean thickness of the specimens (m)

Diffrential scanning calorimetry

Differential thermogravimetric

Empty fruit bunch

Ethylene/vinyl acetate

Fourier Transform Infra Red Spectroscopy

Moduli of filler

Moduli of polymer matrix

Hydrogen chloride

High density polyethylene

Heat Deflection Temperature

Water

Potassium bromide

Span between the centers of support (m) xix

TiO

2

UV

VC

VCM

W

WRHA

W d

W o wt

M

MACR

MBS

M t

NPDE

OH

OPE

PDE

PP phr

PVC

PVC-U

R

RH

RHA rpm

S

SEM

TG

TGA

Tg

Tm -

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Tetravelant base metal (Ti, Zr and Si)

Butadiene-modified acrylic

Methacrylate butadiene styrene

Water content at any time t

Non predefined elastomers

Hydroxyl

Oxidised polyethylene

Predefined elastomers

Polypropylene

Per hundred resin

Poly(vinyl chloride)

Unplasticised poly(vinyl chloride)

Organofunctional group

Rice husk

Rice husk ash

Rotational per minute

Increment in deflection

Scanning Electron Microscopy

Thermogravimetric

Thermogravimetry analysis

Glass transition temperature

Melting point

Titanium dioxide

Ultraviolet

Vinyl chloride

Vinyl chloride monomer

Ultimate failure load (N)

White rice husk ash

Weight after drying

Original weight

Weight percent xx

I

\

W

X

E

R

I m v p

P m

-

-

-

-

-

-

-

-

Increment in load (N)

Hydrolysable group

Relative modulus (of composite to polymer)

Volume fraction of filler

Reduced concentration term

Maximum packing fraction

Poisson’s ratio.

Micrometer xxi

CHAPTER 1

INTRODUCTION

1.1 Introduction

Fillers are defined as materials that are added to the formulation to lower the compound cost. This concept of cost reduction by use of fillers has been known throughout the ages. Very significant advances have been made in this area in terms of fine-particle size technology, tailoring particle morphology, beneficiation of natural materials to attain high purity, surface treatments for improved matrix compatibility, and the development of coupling agents to achieve polymer-to-filler bonding for improved mechanical properties. By the appropriate selection and optimization of such materials, not only the economics but other properties such as processing and mechanical behaviour can be improved. The growing interest in environmental friendly materials has produced re-evaluation of organic materials as fillers in plastics.

Biodegradable and compostable products, especially those made of renewable materials from the disposable agrowastes, are essential for the applications of environmental materials. The organic materials which are abundantly available in quantity are generally less expensive than the resins with which they are compounded, and this is a

2 most important reasons for their use. As the field of plastics developed and expanded, a variety of naturally occurring materials were explored such as wood flour, shell fibres, and empty fruit bunch (EFB).This natural fillers consisting mostly of cellulose, lignin and also hemicellulose.

Utilization of EFB as fillers has been reported by Aznizam and Azman Hassan

(2002). They investigated on the impact properties of empty fruit bunch (EFB) impact modified unplasticised polyvinyl chloride (PVC-U) composites. The results showed that by incorporation of EFB into unmodified PVC-U and modified PVC-U has resulted in the reduction in the impact strength with increasing EFB content. The effectiveness of impact modifier decreased with increasing filler loadings. They also observed that the unfilled PVC-U samples changed from brittle to ductile mode with increasing impact modifier concentration.

Besides that, other natural filler which has attracted many researchers is rice husk (RH). Interest in the use of entire rice husk for the manufacture of composite products is growing up through the year. Rice husk is a by-product of the rice milling process, and there is abundance of rice husk in Malaysia. However, the applications of this material are limited. These include as fuel in heat generation for drying rice, used in making cement, and used as a fertilizer in agriculture. The rest is burned or used for landfilling. Therefore, more efficient utilization of rice husk is urgently needed. One of the efforts is to produce value-added products such as composite materials from this important bio-resources. Utilization of rice husk offers some economical and environmental advantages too. There has been considerable effort and interest in the addition of rice husk to thermoplastic. Many papers have been published on the study of rice husk ash (RHA) and RH as fillers in thermoplastic composites (Ahmad Fuad et al.

1995, Hattotuwa, et al.

2002, Costa et al.

2000 and 2002, Hanafi Ismail, et al.

1999,

Siriwardena, et al.

2002, Visconte et al.

2003; Sae-Oui et al.

2002; and Hanafi Ismail et al.

2002). Most of these study focused on the mechanical properties of the composites.

3

They revealed that the flexural modulus increased with filler content while tensile strength, elongation at break and izod impact strength showed a decrease.

Sivaneswaran (2002) investigated the effect of RHA fillers on mechanical properties of ABS impact modified PVC-U. In this study, ABS was used as impact modifier. He found that the flexural modulus increased as the filler content increased from 0 to 40 phr. However, the impact strength decreased around 40% with the similar filler content.The ABS impact modifier and coupling agents used has improved the impact strength. The formulation containing 8 phr ABS and 40 phr RHA treated with

LICA 12, as coupling agent was found to be the most effective formulation in terms of flexural modulus, impact strength and cost. This study has provided valuable background information on the use of rice husk for making lignocellulosic fillers-PVC-

U composites and prompt us to investigate the performance of rice husk as new filler in thermoplastic composites, especially for polyvinyl chloride (PVC).

In this study, PVC was used as a base polymer as it offers certain advantages.

As the second largest volume plastic used worldwide, PVC plays an important role in the plastic industry (Ma Wenguang et al.

1996). PVC-U is a tough and durable material with many applications where its basic properties effectively meet the demands of service and use (Calvert et al. 1991). Major application for PVC-U is successfully in extrusion products such as pipe, gutters, conduit, sheet and a wide range of complicated profiles such as window frames.

The usefulness of PVC-U can be increased by physically blending various modifiers with the polymer prior to use for plastics objects. These additives such as lubricants, impact modifier, processing aids, pigments and stabilizer are incorporated to modify the service properties of the material and these will in turn influence the processing behaviour (Vinyls Group ICI Petrochemicals, 1981). PVC-U window profile

4 compositions contain a number of components, and the formulations evolve as new materials are developed. Such modifiers, in the context of weatherable compositions suitable for window profiles, include chlorinated polyethylene (CPE), ethylene/vinyl acetate (EVA) copolymers, and polyacrylate rubbers. It is usual to incorporate a rubbery impact modifier into the PVC to improve its robustness in order to use over a wide temperature range .The addition of impact modifiers extends the limits of ductility usually associated with conventional, rigid PVC compounds (Calvert et al.

1991). Thus, it gives more impact efficient and better properties to meet the requirements of extruded profiles.

On this account, the research was focused on the effect of filler loading, impact modifier content, and coupling agent on the mechanical properties of RH filled PVC-U composites, besides investigating the effect of accelerated weathering condition on the mechanical properties of PVC-U composites.

One of the most important aspects in the materials development of engineering thermoplastics 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.

So far, not much study has been reported on RH filled impact modified PVC-U composites. Therefore, in this research where RH was used as a filler in PVC-U to achieve good combination of mechanical properties and processability, several factors

5 that influence and affects the properties of the composites need to be considered. Thus the optimum formulation of the composite was investigated. The questions that need to be answered in this area of research are: i. What is the effect of RH content on the mechanical, weathering, thermal stability and water absorption properties of unmodified and impact modified

PVC-U composites? ii. What is the effect of acrylic impact modifier content on the mechanical, weathering and water absorption properties of RH filled PVC-U composites? iii. What is the effect of coupling agent on the mechanical and water absorption properties of RH filled -acrylic impact modified PVC-U composites? iv. What is the effect of RH and acrylic impact modifier content on the fusion behaviour (torque and fusion time) of the PVC-U composites?

1.3 Objectives of the Study

The objective of this study is to investigate the mechanical, water absorption and weathering properties of RH filled-impact modified PVC-U composites. The objective can be further divided as follows: i. To study the effect of RH content on the mechanical, weathering and water absorption properties of acrylic modified PVC-U composites

6 ii. To study the effect of acrylic impact modifier on the mechanical, weathering and water absorption properties of RH filled-acrylic modified PVC-U composites. iii. To study the effect of coupling agent on the mechanical and water absorption properties of RH filled acrylic impact modified PVC-U composites. iv. To study the effect of RH content and acrylic impact modifier on fusion behaviour (torque and fusion time), and thermal stability of the RH filled

PVC-U composites.

1.4 Significance of the Study

This research developed a PVC-U composite formulation which has a good mechanical properties based on stiffness and toughness, water absorption and weathering properties. Therefore, the use of thermoplastic composite for the development of exterior building applications such as window profile, siding and cladding structure from PVC-U composites at a premium cost, high impact strength and good weathering performance can be achieved.

7

1.5 Scopes of the Study i. The samples preparation involved the following stages:

(a) Dry blending

(b) Two roll milling

(c) Compression moulding. ii. The sizes of fillers of d 75 P m, PVC-U and acrylic impact modifier were used in this research to study the effect on mechanical properties of RH filled acrylic impact modified PVC-U composites. The filler loading was at

10, 20, 30 and 40 phr. iii. Flexural test, tensile test and izod impact test were carried out to determine the mechanical properties of the composites. iv. Water absorption and accelerated weathering test were carried out to study the effect of RH content on the mechanical properties of PVC-U composites. v. SEM (Scanning Electron Microscopy) was used to analyze microstructure and morphology of the composites. vi. Brabender plasticorder was used to study the fusion torque and time of unfilled impact modified PVC-U and RH filled unmodified PVC-U composites. vii. Fourier Transform Infra Red Spectroscopy (FTIR) analysis was used to study the effect of weathering on the degradation of PVC-U composites. viii. Thermogravimetry analysis (TGA) was used to study the thermal stability of the PVC-U composites.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Advances in science and technology have required a variety of new polymers with good performance and low cost. As industrial competition becomes more sophisticated, and end uses more demanding in performance and cost, it will be essential to continue the rapidly expanding use of natural fillers for plastics. Development of organic material as fillers in thermoplastic composites has been a subject of interest for the past few years. The use of natural filler can lead to superior materials, in some cases, at a premium cost, or they can be a means for achieving improved properties while maintaining low costs and stretching the resin supply. The low cost and the good performance of PVC products have increased the utilization of this polymer in exterior of building applications such as window profiles, siding and cladding structure. In the development of window profile from RH filled PVC-U composites via extrusion, good weathering performance and high impact strength are the important requirements.

Therefore, by appropriate formulation in which additives are mixed with the PVC resin

9 and processing, the requirements can be achieved. This chapter reviews the PVC-U properties and the additives that will be used in this research.

2.2 Poly(vinylchloride)

2.2.1 Introduction

PVC is now one of the world’s major polymers and a large amount of PVC is produced worldwide for its superior mechanical and physical properties. PVC can be considered as the versatile plastic. Through proper formulation, PVC has been used in such diverse applications as electrical insulation, medical tubing, including the building industry. PVC as sold in resinous form is unusable. Only by incorporating with suitable additives it can be processed into a useful end product. PVC-U also known as rigid PVC.

Rigid PVC is a material that provides an excellent cost/performance balance with inherent flame retardancy. This material is consequently used in numerous markets and particularly in building and construction applications such as windows, doors, fencing, plumbing, and corrugated sheets (transparent). The versatility of PVC-U can be gauged by the very broad summary of typical end uses given in Table 2.1 (Allsopp, 2003).

Table 2.1 : Typical end uses for PVC-U (Allsopp, 2003)

Application PVC-U

Construction

Domestic

Window frames, gutters, pipes, house siding, ports, roofing

Curtain rails, drawer sides, laminates, audio and video tape cases, records

Packaging

Transport

Clothing

Others

Bottles, blister packs, transparent packs and punnets

Car seat backs

Safety equipment

Floppy-disk covers, credit cards

10

However, unmodified PVC-U has the disadvantage of being prone to occasional brittleness and is notch sensitive. It is always mixed with additives to make processing possible, all of which can influence its physical and mechanical properties. The uniqueness of PVC can be considered under three heading, morphology, versatility and molecular structure.

2.2.2 Structure and Properties

PVC is a polymer which is prepared from vinyl chloride monomer (VCM). The repeating unit structure is represented in Figure 2.1, where ‘n’ denotes the number of repeating unit.

11

Figure 2.1 : Repeating Unit Structure of Vinyl Chloride Monomer

Amongst the range of polymeric materials produced today PVC is unique because the bulky chlorine atom imparts a strongly polar nature to the PVC polymer chain and the essentially syndiotactic conformation of the repeating unit in the chain leads to a limited level of crystallinity. This result in good mechanical properties, particularly stiffness at low wall thickness, high melt viscosity at relatively low molecular mass and the ability to maintain good mechanical properties even when highly plasticized. This enables a wide range of softness and flexibility to be achieved and hence to an even wider variety of end uses.

Most estimates for commercial PVC polymers are of 7–20 % crystallinity.

Since most of the PVC is in the amorphous state, the glass transition temperature (Tg) depends on the molecular structure. The glass transition temperature ,Tg of PVC is usually at 70–80 o C (Kiyoshi Endo, 2002). PVC is never used alone. By adding additives such as heat stabilizers, lubricants, plasticizers, fillers and other additives to make processing possible, the physical and mechanical properties of PVC will be influenced. PVC is not stable when heated and to overcome this problem heat stabilizer must be added. PVC is thermally unstable. Upon exposure to temperature as low as 100 to 120 °C, or upon exposure to ultraviolet radiation, PVC undergoes a degradation reaction.

12

PVC-U is a ductile polymer-vinyls. However it is extremely sensitive to stress rate, temperature and notching. Increasing impact rate, (using a high speed saw), reducing temperature (e.g. installation in a northern winter) or providing a notch as a stress concentrator (as from deep embossing on the surface), can dramatically reduce

PVC’s ductility.

Much work on improvement of the inferior properties of PVC has been carried out besides the addition of additives such as plasticizers, heat stabilizers, lubricants, fillers and other polymers (Anthony, 1999 ) . Examples include blends with acrylic impact modifiers, methacrylate butadiene styrene (MBS) and acrylonitrile butadiene styrene (ABS) has been examined to improve the impact strength. Table 2.2 lists down the properties of rigid (unplasticized) PVC (Mathews, 1996).

Table 2.2 : Typical properties of PVC-U (Mathews, 1996)

Mechanical properties

Elongation at break

Elongation at yield

Stiffness (Flexural Modulus)

25 – 80 %

5 6 %

2.1

3.5 GPa

Strength at break (tensile)

Strength at yield (tensile)

Toughness (Notched izod impact at room temperature) 20 110 J/m

Young modulus 2.4

4 GPa

Physical properties

Density 1.35

1.5 g/cm 3

Radiation resistance

35 60 MPa

35 50 MPa

UV light resistance Fair

13

There are three main processes used for the commercial production of PVC, which is suspension, mass and emulsion polymerization. About 80% of all PVC is produced by the suspension process, 12% by the emulsion process and mass 8%

(Allsopp, 2001). Suspension polymerization is used preferentially in industry to avoid the risk of explosive associated with the bulk process (Kiyoshi Endo, 2002). Majority of material used for extrusion is manufactured by the suspension process. Suspension polymerization is the process that is normally employed in industrial production of PVC.

The polymerization reaction proceeds heterogeneously. In suspension polymerization of

VC (vinyl chloride), both stirring and the state of the system plays an important role determining the morphology of the resulting polymers.

PVC grains are built up from a series of particulate structures of different sizes which determines the grain morphology that influences the processing characteristic and property behaviour. After polymerization, PVC posseses various levels of morphology.

Schematic diagram of PVC powder morphology is shown in Figure 2.2 (Gilbert, 1985).

Powder particles, visible to the naked eye, are known as grains. These are irregular in shape and about 65-150 P m in diameter. Each grain is an assembly of primary particles about 1 P m in diameter. The primary particles are loosely packed together so that the grain is porous. The amount of porosity varying with polymer grade. Each primary particle appear to be made up of still smaller structures (approximately 10-30 nm in diameter), called domains. It is known that PVC contains about 7-20 % crystallinity. The

14 most ordered structures are believed to exist at the center of these domains (Gilbert,

1985). The morphology terminology for PVC to understand the morphological units, is listed in Table 2.3 (Geil, 1977).

Figure 2.2 : Schematic Diagram of PVC Powder Morphology (Gilbert, 1985)

Grain

Term

Table 2.3 : List of Terms for PVC (Geil, 1977)

Approximate size in Origin or description typical PVC

100 P m Free flowing at room temperature

Agglomerates 10 P m Formed during polymerization by merging of primary particles

Primary Particle

P m Formed from single polymerization site at conversions of 10-50%

Domain

Microdomain

P

P m m

Presence not clearly proven, possibly formed by mechanical working within or from primary particles

Crystallite or nodule

15

Summers (1981) examine the nature of PVC crystallinity-the microdomain structure. Figure 2.3 illustrates the microdomain structure of PVC. These crystallites are connected together by tie molecules and have a 0.01 micron spacing. This model explains the reason for the poor interaction of the primary particle flow units in the low temperature melt. Because the material within a primary particle is held together by a three-dimensional network structure, it cannot interact with other primary particles. The ability of PVC to form a wide range of compositions with plasticizers is very important for practical applications. The crystallites act as physical crosslinks in the practical materials (Kiyoshi Endo, 2002).

Figure 2.3 : The Microdomain Structure of PVC

16

2.2.5 Fusion of PVC

Processability of a rigid PVC dry blend is controlled to a large extent by the fusion properties of the compound. There are three major hypothesis that have been proposed to account for the fusions of PVC compounds. The crystallinity theory, the entanglement theory and the PVC particle breakdown theory have been used to explain the fusion process and are commonly employed to explain different parts of the total phenomenon of fusion. The most common idea used in literature to explain the properties of plasticized PVC is that PVC crystallites of a wide melting range and at a separation of about 0.01

P m. The separation act as crosslinks in a 3-dimensional network. The entanglement theory postulates that the molecular entanglements provide the tie points for network formation. In the PVC particle breakdown theory both the crystallinity and entanglement theory have been used in conjunction with the way in which the PVC grains break down to explain the process of fusion (Gilbert et al . 1985).

To obtain good mechanical properties, grain boundaries must be eliminated, and the microparticles must be altered and compacted together. After significant interdiffusion, the boundaries of submicroparticles disappear, and a melt of the polymer is formed. This is called the fusion or gelation, of PVC (Krzewki et al.

1981). The gelation of PVC is related to the crystallinity (Kiyoshi Endo, 2002).

Normally the fusion mechanism of PVC particles, processed in either an extruder or a batch mixer, is a combination of these three patterns. Optimum values of impact ductility and modulus occur prior to 100 % fusion. Although the strength of material increases with an increase in the degree of fusion, the material reaches optimum ductility and then becomes increasingly brittle because of the higher entanglement of the threedimensional network (Chen et al . 2001). Lubrication is the most important factor in influencing the fusion of PVC during processing which in turn may determine the physical properties of final products.

17

2.2.6 Thermal Stability of PVC

Despite of PVC advantageous, PVC exhibits relatively low thermal stability.

Therefore, the resin cannot be used without efficient stabilization. The instability of

PVC is related to its structure. Radical polymerization of VC results in the formation of macromolecule containing a number of different isomeric forms and structural defects.

These factors are of practical importance, since they affect the colour, thermal stability, crystallinity, processing, and mechanical properties of the finished materials (Kiyoshi

Endo, 2002).

PVC thermal degradation studies are very important because they make it possible to develop processing methods for PVC. The thermal degradation of PVC is a two stage process occurring in a wide range of temperature. The degradation of PVC is well studied and known to be a multi-step mechanism involving sequential and competing processes. During the first stage, below 400 o C the evolution of hydrogen chloride (HCl) together with formation of conjugated polyene sequence. Whereas during the second stage, at higher temperatures, the breakage and pyrolysis of the residue of the first stage is produced. Looking at the chemistry of the model reported by Anthony

(1999), as shown in Figure 2.4 that the first step involves loss of HCl to produce a polyolefin (B). This then undergoes two competing degradation reactions to produce either volatiles or a cross-linked intermediate (C). The intermediate then degrades at a higher temperature to produce more volatile materials and a stable char (D). The volatiles evolved from the transition B to C have been reported to be mainly benzene.

18

Figure 2.4: Schematic Model for PVC Degradation (Anthony, 1999)

The degradation of C, which still has the empirical formula (CH) n

involves the evolution of methylated aromatics including toluene and xylenes. These volatile components require proton abstraction from the condensed phase which must lead to carbon enrichment and further cross-linking which may account for the transition C to

D.

The first stage of degradation occurring between 200 o C and 360 o C, while the second stage of degradation, between 360 o C and 500 o C (McNeill et al.

1995). The formation of aromatic compounds such as benzene and toluene, affecting polymer properties. This results in coloring, the solubility of the polymer decreases and the electrical and mechanical properties deteriorate (Kiyoshi Endo, 2002).

Several studies can be found in literatures where the degradation of PVC is studied by thermogravimetric analysis. Radu Bacaloglu et al.

(1994) and Jimenez et al.

(1993) studied on the kinetics of the thermal degradation of PVC. Other authors have

19 studied the behaviour of mixtures of PVC with different components. For example,

Okieimen and Eromonsele (2000), studied the thermal degradation of PVC stabilized with khaya seed oil, and they concluded that khaya seed oil have a potential as a costabilizer for PVC.

Meanwhile, PVC formulations which are designed for outdoor applications, when exposed to the environmental agents such as ultraviolet (UV), rain and humidity play an important part in the evolution of degradation in PVC compounded polymers.

One of the problem for the outdoor application of PVC/ natural fibre or natural filler composites is that terrestrial sunlight can cause photodegradation. Photodegradation process due to ultraviolet (UV) light exposure is of primary importance for products intended for outdoor application (Falk et al.

2000). This degradation is mainly due to the high susceptibility of both PVC matrix and natural fillers or fibres to photodegradation when exposed to such factors as rain, pollutants and UV radiation. Photodegradation results in serious deterioration in mechanical properties and colour change of the material during service life.

Matuana et al.

(2001), investigated the photodegradation and stabilization of rigid

PVC/wood fibre composites exposed to accelerated UV weathering tests using FTIR.

They concluded that the incorporation of wood fibers into a PVC matrix accelerates the photodegradation of the PVC matrix when exposed to UV irradiation. In general, photodegradation of PVC primarily occurs by a radical-type mechanism. When PVC sample is exposed to sunlight or artificial UV radiation, discoloration occurs rapidly due to the formation of alkene or polyene linkages. At the same time, large amounts of hydrogen chloride evolves (dehydrochlorination process) while the polymer chains undergo chain scission and crosslinking, with the expected deleterious effect on the mechanical properties (Matuana et al . 2001).

20

2.3 The Influences of Additives on PVC-U

One of the important way to improve the properties of plastics is to employ additives. Compounding PVC essentially involves adding to the base PVC resin, the components that will allow to be processed into a finished product with desired properties at minimum cost. The common additives added in the PVC-U formulations are lubricant, impact modifier, processing aid, heat stabilizer, pigment and filler.

2.3.1 Lubricant

Lubrication is the most important factor in influencing the fusion of PVC during processing, which in turn may determine the physical properties of final products (Chen et al.

1995). A lubricant, in the present context, can be defined as a chemical compound necessary for minimization of shearing forces during processing (Marshall, 1969).

Lubricants, slip, antiblocking and mold-release agent control the frictional and adhesive properties of plastics during processing and in service. Lubricants also improve the dispersion of pigments and fillers in plastic (Wolf et al.

2002). The result will give a greater ease of fabrication without detriment to the physical properties of the polymer. It can effect heat build up and surface appearance during processing, physical properties, impact strength and also weather resistance. There are usually classified into two categories, which are based on their functions:

21

Internal lubricant can act as plasticizer and thus reduce the heat distortion temperature. Internal lubricants reduce friction between polymer particles and molecules during the melting (plastification) of plastics and transport of the melt. They thus reduce energy consumption on plastication, lower melt viscosity, improve flow properties, increase output of processing machinery, and allow processing under less stringent conditions (Wolf et al.

2002). One of the popular lubricant is stearic acid..

External lubricants reduce the friction and adhesion of polymer melts on hot metal surfaces of processing machinery such as extruder. This reduces abrasion between the polymer melt and the metal, and improves melt flow. Besides that, the gloss, smoothness and regularity of the surface of the plastic will be improved. It can also reduce transparency and impair the printability, cementability and welldability of plastics. Calcium stearate is very common for such formulations.

Generally speaking, external lubricants delay the fusion time of PVC compound and internal lubricants speed the fusion time or have very little effect on it (Chen et al.

1995).The lubricant combination of calcium stearate-stearic acid is very common for such formulations. The effect of calcium stearate and paraffin wax on the progression of fusion of PVC compounds was investigated by a rheological method based on the capillary entrance pressure loss. It was found that calcium stearate could increase or delay fusion. The way in which fusion is affected changes with temperature and the presence or absence of paraffinic wax. Increased calcium stearate levels in compounds with wax enhance the fusion process. Increased calcium stearate levels in compounds

22 without wax decrease fusion at relatively low temperatures but accelerate fusion at higher temperatures. Paraffin wax delays the resin particle breakdown and the fusion process (Krzewki et al.

1981).

Chen et al.

(1995) in their research on the fusion characteristics of PVC, PVC/ chlorinated polyethylene (CPE), PVC/oxidixed polyethylene (OPE), and PVC/CPE/OPE compounds reported that longer fusion time results in higher fusion temperature. Higher fusion temperature results in lower fusion torque. OPE and calcium stearate can be used to speed the fusion time of PVC significantly. With increasing of CPE content in PVC compounds decreased the fusion time. CPE which is an impact modifier, acts as a processing aid that promoted the fusion process, increased the transfer of heat and shear throughout the PVC grains, thus decreased the fusion time (Chen et al.

2001).

Impact modifiers are additives ranging from polymers to inorganic compounds, which are incorporated into plastic compounds to improve impact resistance. Impact resistance is an important attribute required in a plastic for its successful use in many applications. Impact resistance is defined as the ability of a material or a structure thereform to withstand the application of a sudden load without failure (Stevenson,

1995). The function of an impact modifier is to increase the toughness of a brittle, glassy polymer so that it will not break when subjected to impact.

23

All impact modifiers are elastomeric or rubbery in nature, with a lower modulus than the host polymer. The dispersed rubber phase acts to absorb or dissipate the energy of impact in order to stop craze or crack propagation. In order to stop craze propagation and achieve good impact modification, the rubbery phase must be very well dispersed and the impact modifier must be compatible with the host polymer.

Good adhesion is necessary to prevent the cracks from propagating around the elastomeric particle. Impact modifier is a thermoplastic or cross-linked flexible material that is partly compatible with PVC. It forms discrete phase in the PVC matrix which absorbs and dissipates impact energy. PVC is a typical example of brittle thermoplastic at ambient temperatures. In the case of PVC, core/shell modifier can be used to boost the impact performance. For example, three major types of core shell impact modifiers are available, all acrylic impact modifiers, methacrylate/butadiene/styrene (MBS), acrylonitrile/butadiene/styrene (ABS). Wu et al.

(2004) reported on the influence of core-shell structured modifiers on the toughness of PVC. They found that a sharp brittleductile transition occurred at modifier content of 8 g, meanwhile, the notched impact strength was 20 times as high as that of unmodified PVC with the addition of modifier

15 g in 100g PVC resin.

Core shell modifiers are a class of impact modifiers based on a rubbery core surrounded by a shell of higher glass transition temperature, as shown in Figure 2.5.

While the rubber is responsible for much of the impact-modifying performance of the additive the shell also has several important functions, it enables the additive to be isolated and handled conveniently, it facilitates dispersion of the additive into the polymer matrix and it interacts with the matrix to couple the additive to the matrix.

24

Figure 2.5 : Core/shell Impact Modifiers (Stevenson, 1995)

One of the major functions of core/shell impact modifiers in improving the impact resistance of a plastic is to act as stress concentrators located throughout the polymer matrix. The stress concentrations are produced by the large difference that exists between the modulus of the rubbery impact modifier particles and the polymer matrix. Figure 2.6 depicts the stress concentrations that 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 of the modifier particle. The amplified stress decays relatively 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 the equator toward the poles of the modifier of the particle and is greatly reduced from the applied stress near the poles (Stevenson, 1995). While providing sites of stress concentration in the polymer matrix is an important function of impact modifiers, it is probably not the only purpose they serve in improving the impact resistance of polymer. The ability of the rubbery modifier itself to deform, by elongation and/or by cavitation, is likely to be involved and differentiates its effectiveness in many polymer systems from that of rigid filler in improving impact resistance (Stevenson,

1995).

25

Modifier

Particle

Amplified Tensile

Stress at Particle Equator

Tensile Stress

Applied to Material

Reduced Stress at Particle Poles

Stress Level Decays

Rapidly to Applied Tensile

Stress as Distance from

Modifier Increases

Figure 2.6: Stress Distribution in Polymer Matrix Surrounding a Rubbery Impact

Modifier Particle (Stevenson, 1995)

The organic modifiers can be divided into three classifications (Lutz, 1993): x Type I is known as predefined elastomers (PDE). It has a constant ultimate particle size and shape modifiers, are sometimes called discrete particle modifiers. PDE polymers are complex, consisting of a ‘soft’ or ‘hard’ core coated with a complementing shell usually based on monomers such as methyl methacrylate and styrene. Both the core and shell may be polymerized in several stages with varying degrees of cross-linking and/or grafting as appropriate to build the proper structure to give the desired combination of performance properties. Because they retain their emulsion particle size and shape during processing, impact improvement is obtained over a wide range of processing conditions. The major modifiers of this type are MBS, butadiene-modified acrylic (MACR), methacrylate acrylonitrile butadiene styrene copolymers.

26 x Type II known as non predefined (NPDE) particle size and shape modifiers may also be classified as network polymers (NP). CPE and EVA are the major members in this group. Each can be made to be so compatible with PVC, that they act as plasticizers rather than impact modifiers by increasing the chlorine content of CPE and EVA. These modifiers must form a network enclosing PVC primary particles in order to develop the desired impact strength. Type II modifiers assume varying morphologies in the PVC melt depending on the conditions of temperature, time and shear rates encountered in processing.

x Type III known as transitional modifiers due to their crosslinked rubber/elastomer moiety (compound) and sensitivity to processing conditions. ABS is in this type modifier. By varying the ratios of the components, a wide variety of impact, modulus properties in PVC may be obtained.

2.3.2.1 Mechanism of Impact Modification

The function of an impact modifier is to increase the toughness of a brittle, glassy polymer so that it will not break when subjected to impact. Two mechanisms of impact modification which is interrelated are crack stopping and yield promoting.

(i) Crack stopping, whereby the impact modifier stops the propagation cracks initiated by a sudden blow. This function of energy absorption requires the impact modifier to have a degree of adhesion to the PVC continuum, while at the same time maintaining its integrity as a dispersed phase. Proper particle size (ultimate particle size) and efficient distribution of the impact modifier are essential so that the concentration of

27 impact modifier particles is adequate to be at the right place when needed (Lutz and

Szamborski, 1993).

(ii) Yield promoting, whereby the impact modifier lowers the yield point (stress) of the PVC, allowing it to yield or deform rather than fracture when subjected to a sudden blow. This mechanism makes it possible to suppress brittle or catastrophic failures. A contributing mechanism is the generation of heat when the elastomeric-type impact modifier is deformed in a viscoelastic manner. The instantaneous heating of the surronding PVC matrix results in raising the glass transition point to allow yield rather than brittle fracture (Lutz and Szamborski, 1993).

For an impact modifier to be effective in rigid PVC, it must form a disperse phase and maintain this phase under normal processing conditions. Two factors influence the impact strength and brittle ductile transition in rubber toughened plastics blends is the modifier content and the second factor is core-shell ratio (Wu et al.

2004).

Advantages for PVC modified with an acrylic impact modifier including excellent impact strength efficiency at 23 o C and –10 o C, high vicat point and tensile properties. It also gives excellent dimensional stability, excellent weathering performance, low shrinkage and high wells-strength in window frames (Robinovic, 1983).

Impact modifiers with a core/shell structure have an advantage over rubber particles without a shell in that they can be designed and structured to meet the requirements of the new trends in extrusion technology. A core/shell structure is designed to improve the rheology of a PVC melt significantly. This acrylic impact modifier results in more impact efficient and effective elastomers, with rheological characteristics and weathering properties better suited to meet the requirements of extruded profiles (Robin Madgwick and Bernard Cora, 2002).

28

For some applications, weatherability, which is the ability to retain impact and colour when exposed to ultraviolet light, is also important. Some of the major impact modifiers for PVC, such as acrylic modifiers are weatherable, while MBS and ABS are not. Use of weatherable impact modifiers for PVC is growing significantly, driven by its use in construction applications such as siding and door and window profiles.

Processing aids are effective in accelerating the rate of fusion and alter the melt rheology of PVC compounds (formulations). Processing aids appear to play a major role when the breakdown of the particulate structure and the transition from particle flow to molecular flow. The melt rheology statement can be further divided into four group, that promotes homogenous melt, increases melt strength, increases melt elasticity and controls die swell (Dunkelberger, 1986). A homogenous melt is one where there is minimum of primary particles present to minimize melt fracture and shark skin effects.

Copolymers of methyl methacrylate, styrene-acrylic, methacrylate-PVC grafts, and alpha-methyl styrene processing aids are highly compatible with PVC.

Early researchers proposed that the processing aid was involved with the crystalline portion of the PVC structure. However, the hypothesis has changed, and

Bohme (1975) proposed that the processing aid promotes friction between hot processing surfaces and the PVC compound during the fusion process. Menges and

Berndtsen (1976) proposed that the processing aid becomes part of the interstitial putty that initially binds the particles together and thus promotes the fusion process. Gould and Player (1979) suggested that the processing aid increases particle-particle friction and heat transfer thus promoting fusion. Collins and Krzewki (1967) proposed a

29 combination of particle-particle and particle-metal friction processes as the role of the processing aid. As rigid PVC expanded, clear applications were developed where good dispersion of the processing aid was an important property to minimize gel type defects

(Kosior et al .1986). Rigid PVC formulations with processing aids provide more uniform relaxation of the melt thus giving greater melt strength elasticity and better control of die swell. Besides that, more homogeneos melts resulting in more uniform flow over a wider range of shear rates. Long flexible processing aid chain ties together the particle grains.

Processing aids also promotes transition from the primary particles to a stage where crystallite structures occur at lower temperatures and reduce overall heat history of the formulations (Seymour et al.

1986).

The low thermal stability of PVC is very well known. Despite that, processing at elevated temperatures is possible without damage by the addition of specific heat stabilizers. At elevated temperatures, which necessary for thermoplastics processing,

PVC is damaged by dehydrochlorination (release of hydrogen chloride), autoxidation and mechanochemical chain scission. This degradation is caused by the simultaneous sequence of these reactions and must be minimized as far as possible by the addition of stabilizers (Andreas, 1993). Because the changes accompanying degradation are associated with deterioration in the properties of the polymer, it has become practice to process PVC in the presence of heat stabilizers. A general requirement of heat stabilizer listed as follows:

(i) A heat stabilizer must be capable of preventing the dehydrochlorination reaction or at least must be able to retard this reaction (preventive function).

(ii) Additionally the stabilizer should shorten polyene sequences.

30

2.3.5 Pigment

One of the major problems associated with PVC is its sensitivity to weathering and UV irradiation. Pigments are used to impart colour to the PVC product. The most commonly used pigment for outdoors weatherable is titanium dioxide (TiO

2

). TiO

2 together with UV stabilizers are usually incorporated with PVC to protect the polymer from weathering actions (Raghi et al.

2000). The effect of TiO

2

on physical properties of

PVC is determined more by the phr level than by the specific grade. Impact strength is the most important property affected by titanium dioxide. This pigment is readily dispersable and has good chemical stability and hiding power. Almost all grades of titanium dioxide used in PVC formulating have an inorganic coating, which masks the reactive sites on the TiO

2

and improves dispersion and weatherability (Mathew, 1993).

PVC formulations stabilized with tin (Tinuvin P) type of benzotriazole was found are more ductile than the formulations containing a calcium/zinc-epoxidized soybean oil based thermal stabilizer, which presenting higher strain at break and higher impact strength (Real et al.

2003).

The light stability of the PVC composites can be improved quite efficiently with

TiO

2.

This was found by Matuana et al.

(2001) in their research on photoaging and stabilization of rigid PVC/ wood fibre. This photoactive pigment afforded some protection to the samples against photodegradation by retarding the formation of polyene linkages. The significant decrease in the discoloration of pigmented samples treatments showed that the rutile TiO

2 provided stabilization during weathering of the samples.

31

2.3.6 Filler

Incorporation of various types of fillers into a polymer matrix can be used to developed polymer composites with different properties. Fillers can improve the performance of plastics. At first fillers were viewed primarily as extenders for the resin.

Today’s fillers aid processing, reduce shrinkage, provide colour, increase production rates, modify surface finish, improve physical properties and reduce costs. Also, the use of thermoplastics polymers with particulate fillers or short-fibre reinforcements has grown rapidly because of their good processibility and ability to be recycled.

Fillers can be categorized as inorganic and organic. Inorganic fillers such as carbon black, silica, calcium carbonate and talc. Inorganic fillers are not only used as extnders but they also play an important role in improving the electrical and mechanical properties of plastics. However, the attentions of using organic fillers in polymer composites have become a strong competitor to inorganic fillers. Advantages of organic fillers are low cost, low density, biodegradability, non-abrasiveness, recyclability and renewable nature (Rana et al.

2003). Due to these advantages, the utilization of organic fillers derived from agricultural sources such as pineapple, jute, rubberwood, oil palm fruit bunch and rice husk ash in polymer composites has become rapidly expanded.

Organic fillers also provide positive environmental benefits with respect to raw material utilization where pollution causing by large amount of agricultural wastes can be reduce.

The typical properties of filler are listed in Table 2.4 (George Wypych, 1999).

32

Table 2.4: Typical Filler Properties (George Wypych, (1999)

Particle sizes Range from a few nanometers to tens of millimeters

(nanocomposites to pavements or textured coatings)

Particle Shape

Particles Size

Distribution

Spherical, cubical, irregular, block, plate, flake, fibre, mixtures of different shapes.

Monodisperse, designed mixture of sizes, Gaussian distribution, irregular distribution.

Chemical

Compositions

Physical State

Colour

May be inorganic and of an established chemical composition.

May also be a single element, natural products, mixtures of different materials in unknown proportions (waste and recycled materials), or materials of a proprietary composition.

All materials discussed are solids but they might be available in a pre-dispersed state.

Full range of colours from colourless and transparent, with increasing opacity through white to black.

One of the major reasons for using fillers in PVC is to reduce costs. In addition to their savings cost, fillers are required in PVC applications to confer surface finish properties ranging from gloss to matt, to improve resistance to scratching, and to reduce tack. Good filler for PVC should have low oil absorption and therefore reduced plasticiser demand, should be relatively pure, should have no effect on the stability of the polymer, and should be readily dispersible in the system.

33

2.4 Coupling Agents

Coupling agents are commonly applied to improve properties in fibre or particulate-filled composites. Compounding of cellulosic fillers with thermoplastic increases the stiffness of the composites but tends to reduce strength and toughness. The poor strength properties result from a lack of adhesion between the hydrophobic polymer and hydrophilic filler. Therefore, the applications of coupling agents in particulate filled polymer are used to improve dispersion, adhesion and compatibility systems containing a hydrophilic cellulose and hydrophobic polymer and also to enhance the mechanical strength of composites. These agents modified the interface by interacting with both the fibre or filler and the polymer, thus forming a link between the components (Hanafi Ismail et al . 2001).

The most common type of coupling agents presently used are organofunctionasilanes and organotitanates. The other coupling agent that is less readily available due to a higher production cost is the organozirconate group. These coupling agents can be simplified to the general formula of R-M-X

3 where R is the organofunctional group, M is the tetravelant base metal (Ti, Zr and Si) and X is hydrolysable group (Ahmad Fuad et al.

1995). The potential advantage of using the coupling agent method is their natural attraction with both the natural fibre and the resin matrix during curing. Chuah, et al.

(2000) in their research on influence of titanate coupling agent on mechanical properties of talc filled PP composites found that the impact and elongation were improved with the incorporation of LICA 12 in the filled system. Therefore, in this research, LICA 12 was chosen as a coupling agent. The use of coupling agent in RH will be discussed in section 2.6.

34

2.4.1 Mechanism of Coupling Agent

The reaction mechanism of the tetrafunctional organo-metallic compounds based on titanium is believed to occur in three steps. The reaction mechanism is illustrated in

Figure 2.7 (Ahmad Fuad et al.

1997).

Figure 2.7: Bonding Mechanism of Titanate Coupling Agent to RH Filler’s Surface

(Fuad et al.

1997)

35

First the alkoxy group in the coupling agent undergoes pyrolysis process. Water for the hydrolysis may come from the surface or in the PVC-U resin. Next the group reacts with the hydroxyl of the filler surface by hydrogen bond formation. Then, Ti-O cross links are formed between the filler surface and the adjacent functional groups in a condensation reaction with the elimination of water.

Titanate coupling agent reacts with hydroxyl groups resulting in increasing compatibility of filler and matrix interface. Chuah, et al.

(2000), proposed that filler which is irregular in shape, and the agglomeration of fillers due to interparticle force causes the formation of air voids as illustrated in Figure 2.8(a). However, in the presence of titanate coupling agent, the dispersion of filler particles in polymer phase is enhanced by the replacement of water of hydration at the surface filler, with organofunctional titanate causing organic/filler interface compatible. Thus, eliminating air voids in the system. Therefore, it results in deagglomeration and more uniform dispersion in melt blending as showed in Figure 2.8(b). Titanate coupling agent improves the compatibility of filler with polymer, by enhancing their interfacial adhesion. A major problem due to poor dispersion of filler in the matrix could be overcome with the application of coupling agents, therefore enhance the mechanical strength of the composites.

36

Figure 2.8: Mechanism of Filler Dispersion in Polymer Matrix (Chuah et al.

2000)

2.5

Natural Fibre Thermoplastic Composites

Many studies were carried out on the utilization of natural fibre in thermoplastic composites. Oil palm empty fruit bunch (EFB), oil palm frond (OPF), wood fibre, jute, flax, and rice husk ash (RHA) are some of the fibre that received increased attention as a reinforcing component in polymer composites. Most of these studies focused on the effect of filler loadings and filler particle size distribution on the mechanical properties of the composites. Several researchers reported a number of studies on the effect of oil palm fibre in polypropylene (PP), polyester and high density polyethylene (HDPE) composites on the mechanical properties. Rozman et al.

(1998), investigated the mechanical properties of OPF/HDPE composites. They found that the incorporation of

OPF reduced the tensile and impact properties of the composites. Mohd Ishak et al.

(1998) was also reported a similar finding for the EFB filled HDPE composites.

Another study by Rozman et al.

(1998) reported that the incorporation of EFB into PP

37 matrix resulted in the improvement of tensile modulus. However, the impact strength of short jute fibre reinforced PP composites increased with increasing fibre loading (Rana et al.

2003). Many studies have indicated that some property enhancements could be achieved with incorporation of coupling agents. The coupling agent used in EFB-HDPE showed an improvement of tensile and impact strength of the composites by enhancing the filler matrix interaction (Mohd Ishak et al.

1998).

The studies carried out on thermoplastic composites using natural fillers have attracted many researchers. Stiffness, hardness and dimensional stability of plastics could be improved by incorporation of natural fillers. Meanwhile, some adverse effects such as toughness and ultimate elongation suffer by polymers because of the addition of fillers. The addition of filler to polyolefins seeks to reduce production costs with the subsequent change in tensile and impact properties. Researchers as Rozman et al.

(1998),

Hanafi Ismail, (2001) , Mohd Ishak et al.

(1998) have reported that the addition of filler to polymer system resulted in deterioration of tensile and impact resistance. This behaviour was attributed to the poor filler dispersion and poor filler-matrix interfacial bonding thus giving rise to the formation of large filler agglomerates in the polymer matrix, which influence the mechanical properties of the material. The interfacial adhesion between filler and polymer has a determining influence on the mechanical properties of composites. Poor dispersion of fillers give rise to certain detrimental effects such as reduced product life, performance in service, poor product appearance and poor processing characteristics (Hanafi Ismail, 2001). However, to improve mechanical properties through the use of filler is by treating it with coupling agents besides by changing its particle size (Gonzalez et al.

2002).

The size of fillers plays an important role in determining the mechanical properties of filled-thermoplastic composites. As highlighted by Rozman et al. (1998), the size of filler influence the mechanical properties perfectly true even for lignocellulosic fillers. They studied three different sizes of oil palm frond (OPF)

38 particles, 270-500, 180-270 and 75-180 P m. The results showed that samples with smaller fillers size had the highest flexural modulus of rupture, tensile strength, tensile modulus and impact strength as compared to other samples with larger size. This may be attributed to the greater interaction and/or better dispersion of the finer particles in the

PE matrix and also gave relatively higher absorption energy during the fracture process

(Rozman et al.

(1998). A similar observation was reported by Rozman et al.

(2003).

They found that the size of RH played a significant role in the tensile, impact and flexural properties, where smaller size RH produced composites with higher strength.

The size of RH used was 150-180, 180-250 and 250-500 P m. Gonzalez et al.

(2002) in their research on blend of PP/HDPE with two sizes of calcium carbonate (CaCO

3

), also concluded that smaller particle size showed higher Young modulus, elongation at break and impact resistance, and tend to form smaller agglomerates.

To achieve consistency performance in the product properties of thermoplastic composites, properties of the fibres, the aspect ratio, and the fibre-matrix interface in the composites is an important parameters. Thus, it is necessary to concentrate more on the three major aspects, which is fibre modification, resin matrix and coupling agents.

2.5.1 Natural Fibres and Fillers: Compositions and Properties

Climatic condition, age and digestion process influences not only the structure of natural fillers but also the chemical composition. Primarily, natural filler contain cellulose, hemicellulose, pectin and lignin. The properties of each constituent contribute to the overall properties of the natural filler. Rice husk is one of such major agro-waste products and natural filler which contain cellulose, hemicellulose lignin and ash. These chemical constituents of rice husk filler is shown in Table 2.5 (Hattotuwa et al.

2002).

39

The values are percentage by weight. Cellulose is the essential component of all plantfibres. The carbohydrate fraction of plant tissues composed of cellulose and hemicelluloses which are moderate to high molecular weight polymers based on simple sugars. The cellulose polymer is shown in Figure 2.9 (Han and Rowell, 1997).

Table 2.5: Chemical Constituents of Rice Husk Fillers (Hattotuwa et al.

2002)

Cellulose

Hemicellulose

Lignin

Ash

Others

35

25

20

17

3

Figure 2.9 : The Cellulose Molecule (Han and Rowell, 1997)

Hemicellulose is responsible for the biodegradation, moisture absorption and thermal degradation of the fibre as it shows least resistance whereas lignin is thermally stable but is responsible for the UV degradation. The percentage composition for each of these components varies for different fibres. Generally, the fibres contain 60-80 %

40 cellulose, 5-20 % lignin, and up to 20 % moisture (Saheb and Jog, 1999). Table 2.6 gives data for a variety of other biomass materials (Graboski and Bain, 1979).

Table 2.6 : Lignin in Miscellaneous Plant Material (Graboski and Bain, 1979)

Material Wt% of Lignin / Dry Unextracted Material

Rice hulls

Bagasse

40.0

20.3

Peanut shells

Pine needles

Wheat straw

Corncorbs

28.0

23.9

13.9

13.4

Since most thermoplastic are processed at high temperatures, thermal stability of the fibres or fillers is an important aspect in development of natural fibre reinforced composites or natural filler composites. These fibres are lignocellulosic and consist of mainly lignin, hemicellulose and cellulose. The cell walls of the fibres undergo pyrolysis with increasing processing temperature and contribute to char formation. These charred layers help to insulate the lignocellulosic from further thermal degradation. As the first degradation of these fibres occurs at temperature above 180 o C, the typically used thermoplastics as matrix are (polyvinyl chloride), polypropylene and polyethylene with melting temperatures below or equal to the degradation temperature (Gassan and

Bledzki, 2001). Since most thermoplastics are processed at high temperatures, the thermal stability of the fibers at processing temperatures is important. The degradation of natural fibres is related to a curing temperature in the case of thermosets and extrusion temperature in thermoplastic composites. The degradation leads to poor properties such as odor, colour and also deterioration of their mechanical properties. The effects also result in production of volatiles at processing temperatures higher than 200 o C, and cause a porous polymer product with lower densities and inferior mechanical properties

(Saheb and Jog, 1999).

41

Cellulosic fibres are hydrophilic nature and absorb moisture. The moisture content of the fibre can vary between 5 and 10 %. This is a major problem for all cellulose-fibres if used as reinforcement in plastic. The hydrophilic nature of both natural fibres influences the overall mechanical properties, and dimensional variations of the composites. During processing of composites based on thermoplastics, the moisture content results to poor processability and porous products (Saheb and Jog, 1999). Due to these problems, modification and treatment method of the fibre with various chemical agent, was used in order to achieve desired mechanical properties of the composite.

However, natural fibres offer several advantages compared to conventional fibre such as glass-fibres (Bledzki and Gassan, 1999): x x x x

Plant fibres are a renewable raw material and their availability is more or less unlimited.

Natural fibres that used in plastics, at the end of their cycle, to a combustion process or landfill, the released amount of carbon dioxide (CO

2

) of the fibres is neutral with respect to the assimilated amount during the growth.

The abrasive nature of natural fibres is much lower compared to that of glassfibres, which lead to advantages with regards to technical, material recycling or process of composite materials in general.

Natural fibre reinforced plastics are the most environmental friendly materials which can be composted at the end of their life cycle.

42

2.6 Rice Husk Filled Thermoplastic Composites

Many researchers have investigated on the use of rice husk ash (RHA) and rice husk (RH) as filler in thermoplastic composites. Study on the application of RHA in polypropylene (PP) composites and the effect of titanate, zirconate and silane coupling agents was reported by Ahmad Fuad et al. (1995 and 1997). Incorporation of two types of RHA, which is white rice husk ash (WRHA) and black rice husk ash (BRHA) in PP matrix were also investigated by Ahmad Fuad et al.

(1994). These study focused on the influence of coupling agents on the mechanical properties of PP composites. For most of the composites they found that the flexural modulus increased with filler content while tensile strength, elongation at break and izod impact strength showed a decrease. The study by Ahmad Fuad et al. (1995), showed that adding PROSIL 2020 coupling agent into the PP/RHA composites gave the highest enhancement tensile strength, while the impact properties were improved though marginally by LICA 38 and the PROSIL 9234 coupling agents. Similar observation was reported by Hanafi Ismail et al.

(2001) that the incorporation of a silane coupling agent, 3-aminopropyl triethoxysilane (3-APE), improved tensile modulus, tensile strength and stress at yield of the white rice husk ash

(WRHA)/PP/natural rubber composites. Water absorption test resulted in increment with increasing WRHA loading, while the 3-APE coupling agent improved water resistance of the composites.

RHA is produced by thermal degradation (burning process) of rice husk accompanied by removing of the organic fraction. Thus, the growing environmental awareness programs also discourage the utilization of RHA. These factors prompted several researchers to investigate the performance of RH as filler in thermoplastic composites.

43

Hattotuwa et al.

(2002) studied the effect of RH loading in the PP matrix. In terms of mechanical properties, Young modulus and flexural modulus increased, whereas yield strength and elongation at break decreased with increasing in filler loading. Another study was reported by Han et al.

(2004) on the incorporation of RH as filler in PP. They revealed that tensile strength, notched and unnotched izod impact strengths were lowered by the addition of RH. However, tensile modulus increased with increasing RH loading. Rozman et al.

(2003), studied the mechanical and physical properties of polyurethane composites produced with RH and polyethylene glycol. It was found that flexural, impact and tensile properties increased as the percentage of RH or RH hydroxyl groups was increased but started to decrease after exceeding a threshold value. Smaller size of RH was found to produce composites with higher strength. They also reported that water absorption and thickness of swelling increased with increasing percentage of RH.

It has been observed the presence of silica distributies in rice husk. In order to improve the compatibility between the silica of husk and thermoplastic, different coupling agents were suggested to be used for different state of rice husk. A coupling agent that contain silicon in its chemical structure like silane compounds have to be used where silica is exposed on the surface of husk (Park et al.

2003). The methods of processing rice husk as filler for thermoplastics are also important because different processing methods produce surfaces of rice husk which vary in their characteristics, and thus interaction with thermoplastic matrix. Although these materials are known to be advantageous over the neat polymers in term of the material cost and stiffness, their performance in terms of strength is generally lower due to the natural incompatibility of phases of the hydrophilic fibre with the hydrophobic polymer matrix (Park et al. 1997).

The incompatibility of the fibres with the hydrophobic polymer matrix, the tendency to form aggregates during processing, and poor resistance to moisture, influence the performance of the composites. Therefore, special treatment of fibres and fibre-matrix interface is commonly suggested prior to processing leads to good dispersion and significantly improved mechanical properties of the composites.

44

Previous research showed that less study were done in utilization of RHA or RH in PVC matrix. Earlier work on RHA filled PVC composites were reported by

Sivaneswaran (2002). He investigated the effect of RHA fillers on the mechanical properties of ABS impact modified PVC-U. In his study, ABS was used as an impact modifier. The result showed that the flexural modulus increased as the RHA content increased from 0 to 40 phr. However, the impact strength decreased around 40 % with the similar filler content. The ABS impact modifier and coupling agents have improved the impact strength. He reported that the LICA 12 gave the best enhancement in terms of impact strength for rice husk ash (RHA) filled modified PVC-U compared to LICA 38, silane and zirconate coupling agent. LICA 12 were found to be effective compared to

LICA 38 due to the bulky structure. The formulation containing 8 phr ABS and 40 phr

RHA treated with LICA 12, as coupling agent was found to be the most effective formulation in terms of flexural modulus, impact strength and cost.

Most of the studies on natural fibre composites involve the study of mechanical properties as a function of fibre content, effect of various treatments, and the use of external coupling agents. By adding natural fibres, most of the studies have reported that the modulus of the composites were increased, while the elongation, strength and water absorption were decreased. Both the matrix and fibre properties are important in improving mechanical properties of the composites. The tensile strength is more sensitive to the matrix properties, whereas the modulus is dependent on the fibre properties. To improve the tensile strength, a strong interface, low stress concentration, fibre orientation are required. While the tensile modulus is determined by fibre concentration, fibre wetting in the matrix phase and high fibre aspect ratio. The aspect ratio is very important in determining the fracture properties. An optimum bonding level is necessary to achieve good impact strength. The degree of adhesion, fibre pullout, and mechanism to absorb energy are some of the parameters that can influence the impact strength of a short fibre-filled composites (Saheb and Jog, 1999).

45

2.7 Environmental Effects on Polymeric Materials

The environmental effect on polymeric materials, referred to as weathering.

Exposure to the outdoor environment affects not only the polymeric material itself but also other components within the matrix, such as dyes, pigments, processing additives and stabilizers. Most polymeric materials when exposed to the environment are subject to deterioration caused by the combination of all weather factors, including solar radiation, heat, cold, moisture, oxygen and atmospheric contaminants. This will result in low mechanical properties. Complex interactions of the combination of weather factors with the polymer and its components result in irreversible changes in the chemical structures and physical properties and reduces the useful life of the material (Searle,

2003).

Test on weatherability are an essential aspect of the development of new and improved products as well as for quality control and certification of stability specifications. Tests on the weatherability of materials, under natural weather conditions as well as laboratory-accelerated tests have been developed to have relatively good weather resistance. Weather factors such as UV radiation, temperature, moisture, oxygen, humidity and atmospheric pollutants resulted in the deterioration of mechanical properties of the polymeric materials. Prolonged outdoor exposure of all organic polymeric materials leads to appearance changes, such as loss of gloss, formation of surfaces crazes and cracks, chalking, yellowing and fading as well as to breakdown of mechanical properties, including impact strength, tensile strength and elongation properties that are particularly important in some applications (Searle, 2003).

In order to study the durability of composites containing natural fibres, several researchers investigated the degradation and weathering characteristics of the composites. Abu Sharkh and Hamid, (2004) studied the degradation of date palm

46 fibre/PP composites in natural and artificial weathering on mechanical and thermal analysis. They found that, by comparing the stability of PP and the uncompatibilized composite from the diffrential scanning calorimetry (DSC) melting temperatures of naturally weathered samples indicates that the presence of lignocellulosic fibres imparts stability to the composite material. Saheb and Jog, (1999) reported that the thermal degradation of natural fibres is in two stages process. One is in the temperature range of

220-280 o C and the other is in the range of 280-300 o C. They reported that the low temperature degradation process is associated with degradation of hemicellulose whereas the high-temperature process is due to lignin. Matuana et al. (2001) studied the photoaging and stabilization of rigid PVC/wood fibre composites. The results indicated that wood fibres are effective sensitizers and their incorporation into a rigid PVC matrix has a deleterious effect on the ability of the matrix to resist degradation caused by ultraviolet irradiation.

2.8 Effect of Weathering on the PVC-U Composites

The ultimate user acceptance of PVC products for outdoor building applications will depend on their ability to resist the deterioration of their mechanical and aesthetic properties over long periods of exposure. However, one of the major problems associated with PVC is its sensitivity to weathering and UV irradiation. A considerable problem for the outdoor applications of PVC-U composites is that terrestrial sunlight can cause photodegradation. This degradation is mainly due to the high susceptibility of both the PVC-U matrix and fillers to photodegradation when exposed to such factors as longterm solar ultraviolet (UV) radiation, rain, snow and pollutants. Photodegradation results in a serious deterioration in mechanical properties and colour change of the material during services life (Matuana et al.

2001).

47

Titanium dioxide (TiO

2

) together with UV stabilizers are usually incorporated into PVC to protect the polymer from weathering actions. The photo-activity of TiO

2 pigments should result in the formation of oxidation products containing carbonyl groups, originating from radical attack on any unsaturation in the polymer, responsible for the yellowing in PVC (Real et al.

2005).

Photodegradation of PVC proceeds primarily by a radical-type mechanism.

When a PVC sample is exposed to sunlight or artificial UV radiation, discoloration occurs rapidly due to the formation of alkene or polyene linkages. Simultaneously, large amounts of hydrogen chloride evolve (dehydrochlorination) while the polymer chains undergo scission and crosslinking, with the expected deleterious effects on the mechanical properties. This degradation is substantially accelerated by the presence of chromophore materials (impurities) such as carbonyl and hydroperoxide groups within the polymer chain or on side groups. This chropmohoric groups contaminate commercial

PVC and are able to initiate the dehydrochlorination reaction because they effectively absorb the incident light (Matuana et al.

2001). In the presence of oxygen and moisture,

PVC undergoes a very fast dehydrochlorination and peroxidation process with the formation of polyenes and subsequent scission of the chains (Raghi et al.

2000).

Weathering exposure cause polymer degradation can be proven by infrared-spectra and thermal analysis, as well as the changes observed in mechanical properties.

Matuana et al.

(2001) suggested from Fourier Transform Infra-red (FTIR) results that the mechanism of photodegradation of PVC/wood–fibre composite may be similar to that of neat PVC. Leong et al.

(2004) reported that the significance of exposure on the properties of the composites may vary depending on the composite composition or even filler treatment. They also reported that the tensile strength, flexural strength, elongation at break of talc/calcium carbonate filled PP decreased while flexural modulus increased during initial periods of weathering and deteriorate after a long exposure. An interesting finding was also found where the impact strength retained after being exposed for 6

48 months. Raghi et al.

(2000), who studied effect of weathering on PVC/lignin blend found that, a reduction in tensile strength of PVC/lignin blend after it has been exposed to accelerated weathering is due to the chain scission and the elimination of HCl. They conclude that during weathering two competent processes take place simultaneously, chain scission and cross-linking. The effect of weathering on the appearance of all specimen surfaces was also studied by visual inspection of the exposed sides of the samples. PVC composites showed discolouration after it has been exposed to accelerated and natural weathering. It was found that at the end of the weathering, a slight colour

(from white to yellowish) was observed for unfilled PVC-U. They proposed that, it was due to the presence of chromophoric groups, which were formed on PVC under the effect of the UV light.

For RH filled PVC-U composites, the initial colour was brown and this colour changed gradually to dark brown under the effect of UV. However, samples that have been exposed to the natural weathering, changed to light brown colour. No cracks have been observed after this period of weathering for all PVC-U composites. According to

Falk et al.

(2000) who studied the effect of accelerated aging on fading of HDPE and PP based composites, the specimens with higher wood flour content faded somewhat more than the specimens with lower wood flour content. This was due to the tendency of the wood particles to bleach with UV exposure.

CHAPTER 3

METHODOLOGY

3.1.1 Materials

The PVC used in this research was supplied by Industrial Resins Malaysia, Sdn.

Bhd (IRM), is a homopolymer PVC powder with solution viscosity K-66. It is medium molecular weight resins designed for general purpose, rigid and flexible applications.

The chemical properties of PVC-U used and the additives used in the PVC-U formulations are shown in Tables 3.1 and 3.2, respectively.

Table 3.1 : Chemical Properties of Polyvinyl Chloride Resin K-66.

Appearance

K-Value

White Powder

66

Specific Gravity

Degree of Polymerization

1.4

Volatile Matter, Max.(%)

Foreign Matter, Max. (Grain/100g)

Bulk Density (g/cc)

Particle Size %

1000 r 50

0.5

1.5

0.5

r 0.05

0.3

-

Trade Name

Durastrength 200

(D-200)

Thermolite T890

Sak-Cs

PA 20

TR 92

LICA 12

Additives

Table 3.2 : Additives

Types

Impact Modifier Core-shell type acrylic modifier

Manufacturers

Elf Atochem

Reinforcing filler Rice Husk

Stabilizer Tin

Internal Lubricant Calcium Stearate

Bernas Perdana

Sdn. Bhd.

Elf Atochem

Sun Ace Koh

External Lubricant Acid Stearic

Processing Aids Acrylic Polymers Kaneka (M) Sdn.

Bhd.

Pigment

Coupling Agent

Titanium Oxide

Titanate Kenrich

50

51

Rice husk (RH) samples were delivered in a form of powder. The filler size used in this study was less than and equal to 75 P m. A Restsch Shaker was used to separate the RH into the desired size. In order to achieve less than 5 % moisture content, the RH fillers was oven dried for 24 hours at 105 o C. The percentage of moisture content was calculated by using the following formula: where W o

and W d are the original weight and the weight after drying for a specified period, respectively.

The formulations were based upon typical commercial PVC window frames formulations with some modifications. The contents of filler and impact modifier were varied. Tables 3.3, 3.4, and 3.5 show the PVC blend formulations.

Ingredients

PVC powder K=66

Tin Stabilizer

Calcium Stearate

Processing Aid

Titanium Oxide (TiO

2

)

Stearic Acid

Acrylic Impact Modifier

Rice Husk

Table 3.3 : Blend Formulation 1

B1 B2 phr phr phr phr phr phr phr phr

S1 S2 S3 S4 S5 S6 S7 S8

100 100 100 100 100 100 100 100

2 2 2 2 2 2 2 2

0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5

4 4 4 4 4 4 4 4

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

4 8 12

10 20 30 40

52


Ingredients

B3 B5 phr phr phr phr phr phr phr

S9 S10 S11 S12 S13 S14 S15

100 100 100 100 100 100 100 PVC powder K=66

Tin Stabilizer

Calcium Stearate

Processing Aid

Titanium Oxide (TiO

Stearic Acid

2

)

2 2 2 2 2 2 2

0.5 0.5 0.5 0.5 0.5 0.5 0.5

1.5 1.5 1.5 1.5 1.5 1.5 1.5

4 4 4 4 4 4 4

0.6 0.6 0.6 0.6 0.6 0.6 0.6

Acrylic Impact Modifier 4 8 12 8 8 8 8

Rice Husk 20 20 20 10 20 30 40


Ingredients

PVC powder K=66

Tin Stabilizer

Calcium Stearate

Processing Aid

B8 phr phr phr phr

S16 S17 S18 S19

100 100 100 100

2 2 2 2

0.5 0.5 0.5 0.5

1.5 1.5 1.5 1.5

Titanium Oxide (TiO

2

) 4 4 4 4

Stearic Acid 0.6 0.6 0.6 0.6

Acrylic Impact Modifier 8 8 8 8

Rice Husk 10 20 30 40

LICA 12 Coupling Agent 0.5 0.5 0.5 0.5

53

The powdered ingredients (PVC and additives) were subjected to high-shear forces which disaggregate clusters of particles and disperse them uniformly in the mixture. A heavy-duty laboratory mixer was used to blend PVC-U with additives, in order to homogenize the formulation. Each of PVC formulation was mixed for 10 minutes at low speed mixing before being collected. Before the dry blending took place the correct proportions of resin and additives were weighed and mixed appropriately.

The dosages of coupling agent were applied as advised by the manufactures of the respective coupling agents. A commercial grade of LICA 12 supplied by Kenrich

Petrochemicals was used as a coupling agent in this compounding. The recommended dosage of LICA 12 was 0.2 % by weight of PVC plus 0.5 % by weight of RH. The coupling agent was diluted in n-pentane to make up a 5 % solution that was then sprayed onto the PVC. Chemical structure of LICA 12 (neopentyl(diallyl)oxy, tri(dioctyl)phosphatotitanate) coupling agent is shown in Figure 3.1.

54

Figure 3.1 : Chemical structure of LICA 12 coupling agent (Chuah et al.

2000)

3.1.5 Two Roll Milling

Two roll mill was used to mix and sheeted the dry blends of PVC-U compound.

The milling temperature was set at 165 o C, for both rollers. The milling time was about

5 minutes to obtain a good physical appearance of sheet.

For compression moulding, a mould with 5 cavities with dimension 125 (length)

X 13(width) X 3(thickness) mm was used to prepare the test specimens for flexural test while dimension for impact test specimens 63.5(length) X 12.7(width) X 3(thickness) mm. The mill sheets was placed into each mould cavity. A flat sheet mould with dimension of 160mm and 1mm thickness was also used to prepare the test specimens for tensile test. The temperature for compression moulding was set at 185 o C and the pressure applied of 120 kg/m 2 , followed by cooling for 5 minutes. All the molded specimens were than conditioned at room temperature before being tested.

55

3.2 Testing Techniques

3.2.1 Izod Impact Test – Izod [ ASTM D256-88 ]

Impact testing is performed for two reasons. First, impact testing is used to compare the dynamic response of several materials or batches. The results of impact test are used to compare products manufactured by different processing routes or as qualitycontrol parameter for a given process. Second, impact testing is performed to simulate the end-use conditions of a material or product so it can be manufactured to survive impact associated with its intended use. Notched Izod Impact is a single point test that measure materials resistance to impact from a swinging pendulum. Izod impact is defined as the kinetic energy needed to initiate fracture and continue the fracture until the specimen is broken.

In this research, the izod impact test was conducted using IMPats 15 machine manufactured by ATS FAAR, Italy. The specimens of the testing followed the Type II of the ASTM standard as shown in Figure 3.2. The specimens were molded and pressed by using a hot press. Notching was carried out using the notching tool. The notch depth was fixed at 2.6 r 0.02 mm. The test conditions used were as follows:

Velocity = 3.0 m/s

Angle = 90 o

Hammer energy = 7.5 J

56 l (length) x (Dimension) y (Dimension) y k

(Depth behind Notch)

63.5mm

r 2 mm

3.2mm

r 0.2 mm

12.7mm

r 0.2 mm

10.2mm

r 0.1 mm

Figure 3.2 : Specimen Dimension for Izod Testing [ASTM D256 (A)]

3.2.2 Flexural Test [ ASTM D 790-Type 1]

Flexural testing determines the strength of material when a force is applied perpendicular to the longitudinal axis sample. Flexural test was carried out using the

Llyod machine according to the ASTM D790 standard, three point bending system.

Figure 3.3, is a three-point bending system using a simple support beam. A cross-head speed of 3 mm/min was used and the test performed at a temperature of 25 0 C. To retain consistency, a jig that allowed a span of 50 mm was used.

The calculation for flexural modulus and strength are as follows:

Flexural Modulus =

L 3

' W

4 bd 3

' S

Flexural Strength =

3 WL

2 bd 2 where,

W = Ultimate failure load (N)

L = Span between the centers of support (m) b = Mean width of the specimens (m) d = Mean thickness of the specimens (m)

W = Increment in load (N)

S = Increment in deflection

57

Figure 3.3 : Support Span Arrangement for Flexural Testing (ASTM D790).

58

3.2.3 Tensile Test [ASTM D638]

Filler dispersion, degree of filler adhesion and degree of degradation of polymer are the main factors which determine the tensile properties of composites during the processing period. In this research the tensile test was carried out according to ASTM

D638 on a Lyold machine. Dumb-bell specimens 1mm thick was cut from the molded sheets. A crosshead speed of 20 mm/min was used and the test was performed at room temperature. Figure 3.4 shows the specimen dimension for tensile test. Six specimens were being tested for each test.

W-width of narrow section

L-length of narrow section

WO-width of overall, min

LO-length overall, min

G-gauge length

D-distance between grips

R-radius of fillet

RO-outer radius

T-thickness

6 mm

33 mm

25 mm

115 mm

25 mm

80 mm

14 mm

25 mm

1 mm

Figure 3.4: Specimens Dimension for Tensile Test

59

3.2.4 Scanning Electron Microscopy (SEM)

The SEM was used to obtain some information regarding filler dispersion and bonding quality between filler and matrix, and to correlate between fracture surface and energy absorbed. The specimens were chosen after the impact test. The fracture ends of the specimens was mounted on an aluminium stubs and sputter coating with a thin layer of gold to avoid electrostatic charging during examination. Philip XL 40 was used to examine the coated surface.

3.2.5 Water Absorption Test

Water absorption test was used to determine the amount of water absorbed under specified conditions. Factors affecting water absorption include type of plastic, additives used, filler contents, temperature and length of exposure. The specimens were immersed in distilled water at room temperature. The effect of water absorption follows the ASTM D570 standard. The water absorption was determined by weighing the samples at regular intervals. The percentage of water content at any time t (M t

) was calculated as follows:

M t

W w

W d

W d x 100 % where W d

and W w

are the original dry weight and the weight after exposure, respectively.

60

Accelerated weathering test was done according to ASTM G53. An accelerated aging device was used to evaluate the effect of ultraviolet light exposure on various composites as well as the effect of weathering on the degradation of composites properties. Specimens for accelerated weathering were exposed to fluorescent UV lamps and condensation using ATLAS UV Condensation. The parameters that were set are as follows:

UV Test temperature

Condensation Test Temperature

Time Cycle

: 70 O C

: 50 O C

: 4 h UV/4 h Condensation

The duration for accelerated weathering was 4, 7, 21 and 42 days. Moisture at the surface of the samples was removed and left at room temperature before mechanical test was conducted. The mechanical properties of weathered specimens were compared to unweathered specimens.

3.2.7 Processability study (Brabender Plasticorder)

The processability (fusion characteristics) of filled impact modified PVC-U dry blends was studied by using a Brabender Plasticorder. The PVC-U compound was placed into a mixing chamber as a dry powder blend. The RH filled PVC-U samples was mixed and weighed proportionally to prepare samples equivalent to 10, 20, 30, and

40 phr RH loadings. For impact modified PVC-U compound, the acrylic impact modifier were mixed and weighed proportionally equivalent to 4, 8, 10 and 12 phr. All the dry blends were run at temperature of 185 o C for a period of 15 minutes. The rotor

61 speed of 60 rpm was used. The samples in the mixing chamber passed through all stages of fusion. This fusion behaviour was studied by observing the changes of curve torque.

The torque and polymer temperature as a function of time for constant chamber temperature was measured.

3.2.8 Heat Deflection Temperature (HDT)

The heat deflection temperature test was conducted using a Toyo Seiki HDT S-3 tester, following ASTM D 648, with a flexural load of 1.2 kg and heating rate of 2 ± 0.2

O C/ min. The samples standard dimensions of 125(length) X 13(width) X 3(thickness) mm were immersed under flexural load into 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 the deflection temperature under flexural load of the test sample.

3.2.9 Thermogravimetric Analysis (TGA)

Thermogravimetric analysis is one of the techniques most frequently used to study the primary decomposition reactions involving solids, and has been widely used to study the thermal decomposition of polymers. The information provided by this technique is very useful for elucidating the number of different processes which take place (Marcilla and Beltarn, 1996). The thermogravimetric analyzer used for the thermal degradation study was a Perkin Elmer-TGA 7. A uniform heating rate of 10

O C/min was used within the temperature of 30– 950 O C . The amount of sample used for

62 the experiment was approximately 5 to 22 mg. Each sample was placed in an open platinum sample pan. The purge gas was nitrogen at a flow rate of 20 cm 3 /min. The oven was continuously purged with nitrogen during the experiment to remove the release moisture and maintain dry conditions. The onset temperature of a 10 % weight loss deviation from the baseline of thermogravimetric (TG) curve was used as an indicator of the composite’s thermal stability. The differential thermogravimetric (DTG) curve for weight loss was also recorded.

3.2.10 Fourier Transform Infra-red Spectroscopy (FTIR)

Fourier Transform Infra-red spectroscopy (FTIR) analyses were carried out for weathered samples to measure the extent of chemical degradation. The ratio between the sample and potassium bromide (KBr) was at about 1:100 prior to compacting into thin pellet using a 8 tonnes force hydraulic press for 5 minutes. Infrared spectrum were obtained in transmission and was set to operate in the range of 370-2000 cm -1 .

CHAPTER 4

RESULT AND DISCUSSION

This section is divided into three parts. The first parts focus on the mechanical properties of PVC-U composites, followed by the effect of weathering and finally the effect of LICA 12 coupling agents on the mechanical properties of rice husk filled impact modified PVC-U composites.

4.1 Mechanical Properties of Rice Husk Filled Impact Modified PVC-U

Composites

This section will be divided into six sections. Three sections discuss on the effect of acrylic impact modifier content on impact strength, tensile and flexural properties of unfilled and rice husk filled PVC-U samples. While the other three sections discuss on the effect of rice husk content on impact strength, tensile and flexural properties of unmodified and impact modified PVC-U samples.

64

4.1.1 The Effect of RH Content on Flexural Properties of RH Filled Unmodified

PVC-U

Figure 4.1 shows the effect of RH loadings on flexural modulus of unmodified

PVC-U composites. The results showed that the flexural modulus of RH filled unmodified PVC composites at 40 phr RH, was 46 % higher than the unfilled unmodified PVC. The increase of modulus with increasing filler loading showed that the movement of PVC molecules was more difficult with increasing filler content. This trend is consistent with the study conducted by Azman Hassan and Sivaneswaran

(2001) who investigated the effect of rice husk ash (RHA) on the modulus of PVC-U composites. Figure 4.2 shows that flexural strength was constant with RH loading up to

20 phr within the limit of experimental error and slightly decreased at 30 to 40 phr RH.

6

5

4

3

2

1

0

0 10 20

RH (phr)

30 40

Figure 4.1: The Effect of RH Content on Flexural Modulus of RH Filled PVC-U

120

100

80

60

40

20

0

0 10 20

RH (phr)

30 40

Figure 4.2: The Effect of RH Content on Flexural Strength of RH Filled PVC-U

65

The fact that the modulus increased while the strength decreased with increasing filler content is in agreement with the trend observed by Rozman et al. ( 1998a). The agglomerations of the fillers in the matrix, moisture pick-up in the fillers and the weak interfacial bonding could be the main reasons for the reduction in the flexural strength.

All these factors have restricted the stress transfer from PVC-U matrix to the RH filler from taking place during flexural testing. All these factors resulted in filler inability to support stresses transferred from the PVC-U matrix.

Based on the flexural modulus and flexural strength result, it was found that the

RH filler that results in good modulus and strength (at the cross point), was closed to 20 phr rather than at 30 phr RH content as shown in Figure 4.3. Thus, 20 phr RH filler content was chosen as an optimum filler content. Therefore, in further discussion incorporation of 20 phr RH filler was chosen in unmodified and impact modified

66

PVC-U formulation in order to study the effect of impact modifier content with the presence of RH in PVC-U composites.

130

120

110

100

90

80

70

60

50

40

30

20

10

0

0 10

6

5

4

3

2

20

Flexural Strength (MPa)

Flexural Modulus (GPa)

30

1

40

0

RH content (phr)

Figure 4.3: The Effect of RH Content on Flexural Modulus and Flexural Strength of RH Filled PVC-U

4.1.2 Effect of Acrylic Impact Modifier Content on Impact Strength of Unfilled and RH Filled PVC-U

Figure 4.4 shows that for the unfilled samples, the impact strength increased with increasing impact modifiers content from 0 phr (unmodified) to 12 phr. A sharp increase (88%) in impact strength values, which indicates ductile to brittle transition, was observed as the impact modifier loading was increased from 8 to 12 phr. The

67 acrylic impact modifier is a rubbery core structure surrounded by a shell of higher glass transition temperature. The major function of core shell impact modifier besides improving the impact resistance of a plastic is to act as stress concentrators throughout the polymer matrix. The stress concentrations are produced by the large difference that exists between the modulus of the rubbery impact modifier particles and the polymer matrix.

A similar trend of increasing impact strength with increasing impact modifier was reported by Sivaneswaran (2002) in his study on acrylonitrile butadiene styrene

(ABS) impact modified PVC. However his study showed that the ductile-brittle transition occurred between 0 to 8 phr impact modifier content. He concluded that 8 phr acrylonitrile butadiene styrene (ABS) content in unfilled PVC-U was the optimum content in terms of impact strength enhancement. However, the addition of 20 phr of

RH has lowered the impact strength of RH filled impact modified PVC-U. As shown in

Figure 4.5 it can be observed that the impact strength of RH filled impact modified

PVC-U decreased at all levels of impact modifier compared to the unfilled modified

PVC-U (Figure 4.4).

As the impact modifier content increased from 0 to 8 phr, the impact strength increased by 42 %. Unlike the unfilled samples, no significant change was observed as the impact modifier increased from 8 to 12 phr for the filled samples. The results showed that the acrylic impact modifier had a capability to compensate for the detrimental effect caused by the filler by lowering the yield stress of PVC-U matrix and allowing shear yielding rather than fracture when the samples were subjected to the sudden load.

68

120

100

80

60

40

20

0

0 8 12

Figure 4.4: The Effect of Acrylic Impact Modifier Content on Impact Strength of

Unfilled PVC-U

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0.0

0 4

Impact Modifier (phr)

8 12

Figure 4.5: The Effect of Acrylic Impact Modifier Content on Impact Strength of

RH Filled PVC-U (20 phr)

69

A similar trend was also observed by Aznizam Abu Bakar and Azman Hassan

(2002) who investigated the effect of acrylic impact modifier on EFB filled PVC composites. They found that at 20 phr EFB, the impact strength increased from 6.79 to

7.22 kJ/m 2 as the impact modifier increased from 0 to 9 phr. However, this increase in impact strength (about 6 %) was lower as compared to the present finding (42 %).

Therefore, to achieve a good combination of mechanical properties, 8 phr of acrylic impact modifier content was chosen to be used in the RH filled modified PVC-U composites in further formulation. So that, its concentration in the PVC compound will be as low as possible, consistent with toughness requirements and minimize altering the otherwise desirable properties of PVC.

4.1.3 Effect of Acrylic Impact Modifier Content on Flexural Properties of

Unfilled PVC-U and RH Filled PVC-U.

Stiffness as indicated by modulus is one of the basic properties of composites.

One of the reasons of filler incorporation is to increase the stiffness of the resultant material (Zaini et al.

1996). The effects of impact modifier content on flexural properties are shown in Figure 4.6. It was found that the flexural modulus of both unfilled and RH filled PVC-U composites (20 phr) decreased with increasing impact modifier content.

The results also showed that at all impact modifier loadings, the flexural modulus for the unfilled was lower than the RH filled PVC-U composites. The drop of flexural modulus as the impact modifier increases from 0 to 12 phr, are 32 % and 10 % for the unfilled and RH filled PVC-U composites respectively. The decrease in flexural modulus indicates that the composite has become less stiff.

70

5

4

3

2

1

0

0

Unfilled

4 8

Impact Modifier content (phr)

RH filled (20 phr)

12

Figure 4.6: The Effect of Acrylic Impact Modifier Content on Flexural Modulus of

Unfilled and RH Filled PVC-U

Impact modifiers, due to the rubbery nature, is expected to reduce the stiffness of the polymer. The improvement of impact strength but adversely affecting the flexural properties with increasing impact modifier content is agreed by other researchers (Lutz and Szamborski, 1993). By adding impact modifier, the samples showed a rubbery behaviour, which result in excellent improved in elasticity and toughness. Due to that, less stress was used during deformation and therefore flexural modulus decreased. The flexural modulus of the unfilled impact modified PVC-U blends at 8 phr were almost similar to the values obtained on the ABS modified unfilled PVC-U samples at 8 phr

(Sivaneswaran 2002). The addition of 20 phr RH increased the flexural modulus of

PVC-U at all levels of impact modifier content. It is interesting to note that the degree of stiffness enhancement due to the RH filler increased with increasing impact modifier content.

71

Similar trend was found in flexural strength with the addition of acrylic impact modifier as shown in Figure 4.7. Flexural strength decreased with increasing impact modifier loading from 0 to 12 phr. The reduction was about 28 % and 19 % for the unfilled and RH filled PVC-U composites, respectively. With the incorporation of 20 phr RH filler, the flexural strength of 12 phr impact modified PVC-U samples was higher compared to the unfilled samples at about 16 %.

100

95

90

85

80

75

70

65

60

55

50

0

RH Filled (20 phr)

4 8

Impact Modifier (phr)

Unfilled

12

Figure 4.7: The Effect of Acrylic Impact Modifier Content on Flexural Strength of

Unfilled and RH Filled PVC-U Samples

4.1.4 Effect of RH Content on Impact Strength of Unmodified and Impact

Modified PVC-U

72

The optimum impact modifier concentration in the PVC compound will be based on formulation with a good balance of mechanical properties. Although impact modifiers are effective in enhancing toughness, it is expensive and therefore excessive use should be avoided. Furthermore impact modifier decreases the stiffness which is undesirable for composites for structural applications.

Figure 4.8 shows the effect of RH content on impact strength of both unmodified and impact modified of PVC-U composites. It was found that the impact strength decreased with increasing RH fillers content for both blends. There was a relatively sharp decrease in impact strength for unmodified and modified PVC-U upon the addition of 10 phr RH followed by a gradual decrease upon increasing filler loading.

In the filled composites as the filler loading increased the tendency for agglomeration was also increased. As filler agglomeration increased, interfacial adhesion became weaker leading to weaker interfacial regions (Azman Hassan and Sivaneswaran, 2001).

Therefore, a reduction in impact strength was observed. This result is expected for the filled systems and has been reported by Sivaneswaran (2002) and Aznizam Abu Bakar and Azman Hassan. (2002), in their study on PVC-U composites. With addition of 10 phr of RH for unmodified PVC-U, the impact strength decreased by 25 %, which is 19

% higher compared to RHA filled unmodified PVC-U at similar filler content as reported by Sivaneswaran (2002). However, with increasing filler content from 10 to 40 phr, RH fillers resulted in smaller reduction of 16 % compared to RHA fillers, 31 %.

It is also interesting to observe that the addition of impact modifier has enhanced the impact strength of PVC-U samples at all levels of RH content. The effectiveness of the impact modifier however, decreased with increasing RH content. This result is in

73 agreement with other researchers (Sivaneswaran, 2002, Lutz, 1993 and Yee Joon Wee,

2000). Poor adhesion of the filler and matrix becomes dominant and weakens the stress transfer from the polymer matrix to the filler and deteriorated the impact strength at higher filler loading (Sriwardena et al.

2002). As the filler content increased from 10 to

40 phr, it was observed that the impact strength reduce to about 45 % for the modified

PVC-U. It was found that the difference in impact strength between unmodified and impact modified PVC-U composites becames smaller as the RH content increased. This was due to the predominant of fillers in the PVC-U matrix, therefore resulted in a smaller difference of 2 % at 40 phr RH content in impact strength of both composites.

14

12

10

8

6

4

2

0

0 10

Modified

20

RH (phr)

30

Unmodified

40

Figure 4.8: The Effect of RH Content on Impact Strength of Unmodified and

Impact Modified PVC-U

The reduction of impact strength could be due to two factors. The first factor could be due to the detrimental effect of filler because the volume they take up, thus affect on the impact performance. RH filler unlike the matrix was incapable to dissipate stress through the mechanisms known as a shear yielding prior to fracture. It might also

74 hinder the local chain motions of the PVC molecules that enable the matrix to shear yield (Stevenson, 1995). As a result, the ability of filled composites to absorb energy during fracture propagation was decreased.

Secondly, it is known that the composite materials with satisfactory mechanical properties could only be achieved if there is a good dispersion and wetting of filler in the matrix that will give rise to a strong interfacial adhesion. However, this is not the case when RH fillers are used in PVC. Although the polarity of RH fillers capable to form a physical interaction with the polar PVC but it is a relatively weak interaction compared to the filler-filler interaction caused by hydrogen bondings. Therefore, RH fillers have a greater tendency to agglomerate among themselves which consequently, lowers the area of contact with the matrix. Meanwhile, the moisture absorbed may also interfere the physical bonding between RH fillers and PVC, and potentially acting as a lubricant to the filler-matrix interphase (Sombatsompop and Chaochanchaikul, 2004).

These factors increase the weakness of interfacial adhesion between fillers and matrix, and become the potential sites crack growth as inability of fillers to support the stress transfer to the polymer matrix (Rozman et al. 1998a). All these reasons are likely to be responsible for the decrease in impact strength of composites.

4.1.5 Effect of RH Content on Flexural Properties of Unmodified and Impact

Modified PVC-U.

Figure 4.9 shows the effect of RH loadings on flexural modulus of unmodified and impact modified PVC-U composites (8 phr impact modifier). It was found that the flexural modulus of the unmodified was higher than the impact modified PVC-U samples at all filler loadings. There was a considerable increase in flexural modulus

75 with increasing RH content from 0 to 40 phr. The addition of 40 phr RH increased the flexural modulus of RH filled impact modified PVC composites by 59 % higher compared to the unfilled impact modified PVC. While flexural modulus of RH filled unmodified PVC composites at 40 phr RH, was 46 % higher than the unfilled unmodified PVC. As mention before, RH are able to impart a significant improvement in stiffness by hindering the movement of PVC molecules. The movement of PVC molecules was more difficult with increasing filler content. However, the addition of

RHA in impact modified PVC-U gave lower result in flexural modulus compared to the

RH filled impact modified PVC-U composites at all RHA loadings. As reported by

Azman Hassan and Sivaneswaran (2001), the addition of 40 phr RHA increased the flexural modulus of RHA filled PVC-U composites by 44 %, compared to the unfilled impact modified PVC-U.

6

5

4

3

2

1

Modified Unmodified

0

0 10 20

RH (phr)

30 4 0

Figure 4.9: The Effect of RH Content on Flexural Modulus of Unmodified and


76

A study conducted by Ahmad Fuad et al.

(1997) on white rice husk ash (WRHA) filled PP composites also revealed that the flexural modulus at all WRHA loading was lower compared to RH filled unmodified PVC-U composites as discussed earlier in this study. Compared to the study by Premalal et al . (2002) on the effect of RH filled PP composites, at similar RH content (30 phr), the flexural modulus of RH filled PP composites was lower than RH filled unmodified PVC-U composites. Incorporation of

RH fillers in PVC-U matrix, was found to give the best enhancement in flexural modulus compared to RH fillers in other polymer and RHA in PVC-U composites

(Azman Hassan and Sivaneswaran, 2001). In a two-phase composite made up of a continuous matrix and particle fillers, the type, concentration, size, shape and orientation of the filler particles are important factors in determining the mechanical and physical properties. Among several other factors that can greatly affect the mechanical behaviour of filled systems are the strength of the adhesive bond between different phases, the type of dispersion and the amount of particle agglomeration (Tavman,

1997).

Modulus of composites has been represented by a number of models. The simplest theoretical equation is Einstein’s equation [Eq. (1)], which is valid only at low concentrations of filler when there is perfect adhesion between the phases:

E

R

= (1 + 2.5 I ) (1) where E

R

is the relative modulus (of composite to polymer) and I is the volume fraction of filler (Nielsen, 1974). Einstein’s equation implies that the stiffening or reinforcing action of a filler is independent of the size of the filler particles. This equation also shows that it is the volume occupied by the filler, not its weight, that is the important variable. The equation also assumes that the filler to be very much more rigid than the matrix.

77

For low aspect ratio fillers, the most frequently used model is the Lewis-Nielsen equation [Eq. (2)] (Lewis and Nielsen, 1970):

E

R

= (1 + AB I f

)/ (1 B \I f

(2) where

A = (7 5 v p

) / (8 10 v p

B = [(G f

/G p

) – 1] / [(G f

/G p

) + A]

\ > I m

) I

2 m

] I f

(2b)

(2c)

A is a constant related to the Einstein coefficient and is a function of the filler’s geometry, B is related to the relative moduli of filler and polymer, I f

is a volume fraction of filler and \ is a reduced concentration term dependent on the maximum packing fraction I m

of the filler in the polymer. G f

and G p

are the moduli of filler and polymer matrix respectively, and v p

represents Poisson’s ratio. Table 4.1, presents the comparison of the modulus data for RH filled unmodified PVC-U composites with some of the predictive models of two-phase composites which take into account the shape, packing fraction and adhesion between the filler and the matrix of polymer.

Poisson’s ratio v p

of PVC was assumed to be 0.39 (Fried, 2003). It was assumed that the rice husk particles were spherical in shape, well dispersed and experience random packing. As such the value of the maximum packing fraction I m

was 0.64 as used by

Lewis and Nielsen while deducing the above series of equations. The modulus of rice husk (G f

) was assumed to be 72 GPa equivalent to the value reported by Sivaneswaran

(2002) for the modulus of rice husk ash. Using the above values and substituting into equations (1, 2 and 2a-c) the theoretical modulus for various filler loading was calculated. The comparison values between relative flexural modulus of RH filled impact modified PVC-U composites from experimental value, Einstein and Lewis-

Nielsen or modified Kerner equations are given in Table 4.1. It can be concluded that the results give a better agreement with the Einstein equation. These results are in agreement with the study conducted by Sivaneswaran (2002).

78

Table 4.1 : Relative Flexural Modulus Value of Composite to Polymer

RH

Content (phr)

Experimental

Value

Einstein

Equation

Lewis and Nielsen

Equation

10

20

30

40

1.12

1.18

1.33

1.46

1.08

1.16

1.23

1.29

1.07

1.13

1.19

1.25

Figure 4.10 shows the result of flexural strength for both types of composites.

Flexural strength increased with RH loading up to 20 phr and slightly decreased at 30 to

40 phr RH for unmodified PVC-U composites. However, flexural strength for impact modified PVC-U composites increased at 30 phr and decreased at 40 phr. The difference between both composites became smaller at 30 and 40 phr RH contents.

120

100

80

60

40

20

Unmodified Impact Modified

0

0 10 20

RH (phr)

30 4 0

Figure 4.10: The Effect of RH Content on Flexural Strength of Unmodified and

Impact Modified PVC-U , 8 phr impact modifier

79

The trend is similar with the study reported by Rozman et al.

(2003) on the mechanical and physical properties of polyurethane composites based on rice husk and polyethylene glycol where flexural strength increased up to a certain extent of RH content, after which it decreased. The increased in the amount of RH has subsequently reduced the ability of stress transfer. Therefore, decreased the flexural strength of the composites.

4.1.6 Effect of Acrylic Impact Modifier Content on Tensile Properties of Unfilled and RH Filled PVC-U

The effect of impact modifier on tensile strength and Young modulus are shown in Figures 4.11 and 4.12, respectively. In the presence of acrylic impact modifier in RH filled PVC composites (20 phr RH), it decreased the tensile properties (tensile strength and Young modulus). Tensile strength of the samples decreased up to 18 % for the RH filled and 28 % for the unfilled impact modified PVC-U samples with the addition of 4 to 12 phr loading of acrylic impact modifier (Figure 4.11). The impact modifier acted as a yield promoting whereby it lowered the yield point (stress), allowing the PVC to yield or deform rather than fracture. Incorporation of RH filler decreased the tensile strength of RH filled PVC-U composites at all impact modifier contents.

80

80

60

40

20

RH Filled Unfilled

0

0 2 4 6 8

Impact Modifier Content (phr)

10 12

Figure 4.11: The Effect of Acrylic Impact Modifier Content on Tensile Strength of

Unfilled and RH Filled PVC-U , 20 phr

3

2.5

2

1.5

1

0.5

RH Filled Unfilled

0

0 2 4 6 8

Impact Modifier Content (phr)

10 12

Figure 4.12: The Effect of Acrylic Impact Modifier Content on Young Modulus of

Unfilled and RH Filled PVC-U , 20 phr

81

4.1.7 Effect of RH Content on Tensile Properties of Unmodified and Impact

Modified PVC-U

Figure 4.13 shows the effect of RH loading on tensile strength of PVC-U composites. In general, tensile strength decreased with RH loadings. This is not surprising since other studies have also indicated that the incorporation of filler into thermoplastic matrix may not necessarily increase the tensile strength of the composites

(Han et al.

2004 and Mohd Ishak et al.

1998). Tensile strength for the unmodified PVC-

U was higher compared to the impact modified PVC-U at all RH loadings. With the addition of 10 to 40 phr RH, tensile strength decreased to about 17 and 10 % for the unmodified and impact modified PVC-U samples respectively. The tensile strength decreased as the filler loading increased may be attributed to the reduction in deformability of a rigid interface between filler and the matrix component (Hanafi et al.

1999).

80

70

60

50

40

30

20

10 Unmodified Impact Modified

0

0 10 20

RH fillers content (phr)

30 4 0

Figure 4.13: The Effect of RH Content on Tensile Strength of Unmodified and


82

As the filler loading increased, thereby increasing the interfacial area, the worsening interfacial bonding between filler (hydrophilic) and matrix polymer

(hydrophobic) decreased the tensile strength (Han et al.

2004). The deterioration of tensile properties indicates the incapability of filler particles to support the transfer of stress from the matrix to the filler (Siriwardena et al.

2002). RH fillers, which exist as an irregular-shaped, have poor capability to support stress transmitted from the thermoplastic matrix. Therefore, lowering the stiffness and strength improvement of the composites.

However, incorporation of RH into a PVC-U matrix has resulted in the improvement of Young modulus for both RH filled unmodified and modified PVC-U composites. The effect of different loadings of RH on Young modulus is illustrated in

Figure 4.14. At 40 phr RH content, Young modulus improved by 31 % for impact modified PVC-U, while unmodified PVC-U improved about 27 %. Similar effects were observed by other researcher who studied the incorporation of particulate fillers including RHA into plastics (Siriwardena et al . 2002). Fillers are known to increase modulus provided the modulus of the filler is higher than that of the polymer matrix

(Siriwardena et al . 2002). Similar trend to flexural modulus was observed which indicates the ability of RH fillers to impart greater stiffness to the PVC-U composites.

83

2.5

2

1.5

1

0.5

Modified Unmodified

0

0 10 20

RH (phr)

30 40

Figure 4.14: The Effect of RH Content on Young Modulus of Unmodified and


84

4.2 Effect of Weathering on Mechanical Properties of Rice Husk Filled Impact

Modified PVC-U Composites

This section discuss the effect of weathering on flexural properties, impact strength and tensile properties of RH filled impact modified PVC-U composites.

4.2.1 Effect of Weathering on Flexural Properties of RH Filled Impact Modified

PVC-U

The effect of accelerated weathering on flexural modulus of RH filled impact modified PVC-U is shown in Figure 4.15. A similar trend of result was observed for all the composites. There was an increment in flexural modulus after 4 days of exposure followed by a gradual decrement in flexural modulus when samples were exposed for more than 4 days. During weathering, two competent processes take place simultaneously, that are chain scission and cross-linking. This explains the variation of the mechanical properties with the weathering period. The increment can be attributed to the enhanced stiffness of the composite caused by photo-oxidation. A similar trend was reported by Leong et al. (2004), who studied on the characterization of talc/calcium carbonate filled polypropylene hybrid composites weathered in a natural environment.

They reported that, influence of crosslink chains in the sample resulted in the increase of the flexural modulus. The photo-oxidation degradation process which took place mainly in the amorphous region of PVC-U because of the higher permeability of oxygen led to intermolecular crosslink, while others to the chains scission. The enhancement in the properties of weathered samples was similar with the finding of other researchers (Raghi et al.

2003).

85

After 42 days, flexural modulus decreased by 4 % for sample at 20 and 40phr

RH, while sample at 30 phr decreased by 8 %. Only sample at 10phr RH loadings showed an increment in flexural modulus, about 11 % after it has been exposed for 42 days. With the presence of moisture, a large number of hydrogen bonds between the macromolecules of the RH filler and polymer are broken and new hydrogen bonds with water molecules are then formed and these could cause decrement in the mechanical properties of the composites (Sombatsompop and Chaochanchaikul, 2004). The reduction could also be attributed to the reduction of PVC molecular weight, due to the chain scission taking place as the predominantly when exposure time increases.

6

5

4

3

2

1

PVC/RH10/IM8

PVC/RH20/IM8

PVC/RH30/IM8

PVC/RH40/IM8

0

0 7 14 21 28 35 42 49

Days

Figure 4.15: The Effect of Accelerated Weathering on Flexural Modulus of RH

Filled Impact Modified PVC-U

It was found that flexural modulus increases with increasing RH content for all exposure time. As would be expected, composites with higher RH content showed the highest flexural modulus. Overall, there was no any significant changes in flexural

86 modulus. This is due to the photo-oxidation degradation mainly occurred on the surface of sample, thus the contribution of RH in enhancing the flexural modulus of the weathered sample composites relatively similar as the unweathered ones.

Figure 4.16 shows that there was an increase in flexural strength at 4 days of exposure for all composites. However, a gradual decrement in flexural strength were observed after being exposed for more than 4 days. At the end of weathering period, samples at 30 and 40 phr RH contents, decreased by 7 % and 5 %, respectively.

However, composites at 10 and 20 phr RH filler, flexural strength decreased about 9 and 4 %, respectively. Leong et al.

(2004) reported that flexural properties are usually more sensitive to the surface of the specimens. Therefore, the explanation for the changes in flexural strength is similar to those results for flexural modulus. The significant changes may probably occur after longer of time of exposure, more than 42 days.

120

100

80

60

40

20

PVC/RH10/IM8

PVC/RH20/IM8

PVC/RH30/IM8

PVC/RH40/IM8

0

0 7 14 21

Days

28 35 42 49

Figure 4.16: The Effect of Accelerated Weathering on Flexural Strength of RH


87

4.2.2 Effect of Weathering on Impact Strength of RH Filled Impact Modified

PVC-U

Figure 4.17 shows the effect of accelerated weathering on impact strength of RH filled impact modified PVC-U composites. It shows that impact strength decreases as the filler loading increased at each duration of exposure. At the beginning of exposure at 4 days, impact strength showed a slight increment for composites at 10 and 30 phr , while composites at 20 and 40 phr showed a reduction compared to unweathered samples. Similar trend was found by Real et al.

(2003) in their research on accelerated weathering of PVC where compounds which stabilized with tin stabilizer, resulted an increment of impact strength at the beginning of weathering exposure and decreased after an extended period. At 42 days of exposure, impact strength decreased for composites at 10 phr RH content compared to unweathered composites. 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 composites. However, composites at

20, 30 and 40 phr RH exhibited a slight increment at 42 days exposure. Leong et al.

(2004) suggest that only the surface of the specimen is subjected to embrittlement.

Therefore, only a slight increment in impact strength were observed. As reported by

Leong et al.

(2004), build up of aromatic compounds causes by pollution on the surface of samples, combined with hydroperoxides as well as carbonyl groups might form during photo-oxidation. This could be the main reason that causes the embrittlement of the composites.

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 causes material embrittlement (Gardiner et al.

1997). The photodegradation process substantially accelerated by the presence of chromophore materials (impurities) such as carbonyl and hydroperoxide groups occurs within the polymer chain or on side groups. These chromophoric groups contaminate commercial

88

PVC and are able to initiate the dehydrochlorination reaction, while the polymer chains undergo scission (Matuana et al.

2001). Extensive chain scission in the samples, causing the breakdown of tie chain molecules and entanglement, which are especially detrimental to the ductility of the polymer. Most researchers agreed that crosslinking and chain scission contribute to the deterioration of the impact strength and other mechanical properties (Matuana et al.

2001).

1

0

4

3

2

0

9

8

7

6

5

PVC/RH10/IM8

PVC/RH20/IM8

7 14 21

Days

28 35 42

Figure 4.17: The Effect of Accelerated Weathering on Impact Strength of RH

Filled Impact Modified PVC-U Samples

49

A slight decrement in impact strength for composites at 10 phr RH content compared to unweathered composites at 42 days of exposure might be due to the acrylic modifiers which are in “weatherable” category. Meanwhile, RH fillers which tends to agglomerate created stress concentration points that causes weakness and consequently decreased the impact strength of the composites.

4.2.3 Effect of Weathering on Tensile Properties of RH Filled Impact Modified

PVC-U

89

The effect of accelerated weathering on tensile strength of RH filled impact modified PVC-U samples are shown in Figure 4.18. Various trends of result are observed with increasing exposure period. After 4 days, tensile strength exhibit a decrement for all composites except for sample at 20 phr RH loadings. Tensile strength decreases after exceeding 21 days of exposure for all composites except sample at 10 phr RH content which increases until at the end of the period. In general, tensile strength for all composites decreases after samples have been exposed for 42 days compared to unweathered sample. After 42 days, tensile strength decreased by 4 and 14

% for sample at 10 and 20 phr RH content respectively. While sample at 30 phr and 40 phr decreased by 19 and 14 % respectively.

of polyvinyl chloride/lignin blends proposed that, after weathering the changes in tensile strength indicate that whether cross-linking or chain scission (breaking) of the polymer has occurred. They proposed that a decrease in the tensile strength is due to the chain scission and the elimination of hydrogen chloride (HCl). While an increase in tensile strength is caused by the predominant process of cross-linking occurring under the effect of weathering action. Tensile strength is known to involve the ability of polymer molecular chains to slip past each other, the more difficult the slippage of the molecular chains the greater the tensile strength (Sombatsompop and Chaochanchaikul,

2004).

90

70

60

50

40

30

20

10

PVC/RH10/IM8

PVC/RH20/IM8

PVC/RH30/IM8

PVC/RH40/IM8

0

0 7 14 21

Days

28 35 42 49

Figure 4.18: The Effect of Accelerated Weathering on Tensile Strength of RH


The Young modulus for samples exposed under accelerated weathering is shown in Figure 4.19. The Young modulus decreases for all samples at the end of the exposure period. The Young modulus increases up to 4 days of weathering exposure and decreases with increasing time of exposure except for 40 phr RH. At the end of weathering exposure, the reduction of Young modulus was about 15 to 35 % for all composites compared to unweathered samples. The increase in the properties at 4 days of weathered samples indicated that the influence of crosslinking and chain scission of

PVC molecular chains in the composites might cause a slight increase in the Young modulus. Other factors such as filler agglomerations and filler interaction might influence the Young modulus result for composite at 40 phr RH at 4 days exposure. As mentioned earlier, crosslinking and chain scission contribute to the deterioration of the mechanical properties of the composites (Matuana et al.

2001).

91

2.5

2

1.5

1

0.5

PVC/RH10/IM8

PVC/RH20/IM8

PVC/RH30/IM8

PVC/RH40/IM8

0

0 7 14 21

Days

28 35 42 49

Figure 4.19: The Effect of Accelerated Weathering on Young Modulus of RH


4.2.4 Fourier Transform Infrared Spectroscopy (FTIR) Analysis

In order to study the effect of UV-irradiation on the mechanical properties, FTIR analysis was done to asses the extent of degradation and the structural changes of the composite under accelerated weathering conditions. Figure 4.20 shows the spectra of the PVC-U composites before and after weathering with respect to the time of exposure.

The accelerated weathering duration was 4 days, 1 week, 3 weeks and 6 weeks. In this study, PVC-U composites at 30 phr RH content was chosen as it give the same results with samples at others RH content. The spectra of the composites is between 2000 and

350 cm -1 . When PVC samples was exposed to sunlight or artificial UV radiation, discoloration occurs rapidly due to the formation of alkene or polyene linkages.

92

Simultaneously, HCl evolve (dehydrochlorination) while the polymer chains undergo scission and crosslinking, with expected deleterious effects on the mechanical properties

It can be observed that, after samples were exposed under accelerated weathering conditions, it is clearly showed that a band appeared at 1431 cm -1 ,1433 cm -1 and 1639 cm -1 1653 cm -1 compared to the unweathered samples. According to Beltran et al. (1997), bands between 1650 and 1550 cm -1 correspond to the C=C bonds. Bonds of C=C indicate that dehydrochlorination of PVC molecules took place with the formation of conjugated double bonds. The presence of alkene and polyene linkages was considered responsible for the photodegradation of the composites. While bands at

1400-1500 cm -1 were due to the wagging of the methylene groups. Therefore, bands that appeared at 1639 cm -1 provide a good evident for the presence of C=C bonds, which is formation of unsaturated vinyl groups (RCH=CH

2

) by photo-oxidation degradation process.

Sharp bands at 1431cm -1 and 1433 cm -1 due to the =C-H out of plane bending were detected and very intense with increasing times of exposure from 4 days to 6 weeks. The increase of intensity were also indicative of photo-degradation samples upon exposure to UV light. It has been confirmed that the bands was attributed by the process of decomposition of the PVC (Matuana et al.

(2001).

Band at 1729 cm -1 as shown in Figure 4.20 was due to the presence of carbonyl groups of C=O in the cellulose with addition of RH. Matuana et al.

(2001) found that the band at 1731 cm -1 was corresponded to the carbonyl groups, with incorporation of wood fiber. However, it was found that the intensity of the absorption band at1729 cm -1 for sample under accelerated weathering increased with increasing time of exposure.

The significant increase of this absorption band (intensity) may be due to the increased

93 of functional groups containing carbon-carbon double bonds (R

2

-C=C) conjugated to carbonyl groups (Matuana et al.

(2001). These groups were able to absorb the incident light effectively and initiate the dehydrochlorination reaction of the PVC occurred substantially. The conjugated double bonds and carbonyl groups leads to the degradation or cross-linking of PVC.

4.3 Effect of Coupling Agent on Mechanical Properties of RH Filled Impact


95

This section discuss on the effect of LICA 12 coupling agent on flexural properties, impact strength and tensile properties of RH filled impact modified PVC-U composites.

4.3.1 Effect of Coupling Agent on the Impact Strength of RH Filled Impact


Figure 4.21 shows the impact strength of rice husk filled impact modified PVC-

U composites as a function of coupling agent and filler content in composites. The effects of LICA 12 coupling agent can be assessed by comparing the results of treated and untreated composites. It showed that LICA 12 was effective in increasing impact strength. These results are in agreement with the results reported on impact strength of

RHA filled PVC-U composites (Azman Hassan and Sivaneswaran, 2001). As both rice husk and PVC-U are polar, it is expected that interfacial region is good enough and from this result it is discovered that the usage of LICA 12 improved the impact strength.

LICA 12 improved the impact strength by 26 % at 20 phr RH, followed by 18 % at 30 phr RH and 6 % for composites at 40 phr RH content.

The impact strength clearly decreased as the filler content increased, in both composites. The decrease in untreated composites from 0 to 40 phr of filler content was about 39 %, which is greater compared to reduction for samples treated with LICA 12, about 30 %. The use of coupling agent, certainly enhanced the adhesion capacity at the

96 interface and improved the compatibility between filler and polymer matrix. Toughness is the major factor that controls the impact strength. During impact test, a crack travels through the polymer and interfacial region. High filler-matrix interfacial adhesion provides effective resistance to crack propagation during impact test. Thus, improved the impact strength of the composites (Chuah, et al.

2000).

4

3

2

1

0

10

8

7

6

5

Sample with coupling agent

Sample without coupling agent

20

RH Content (phr)

30 40

Figure 4.21: The Effect of Coupling Agent on The Impact Strength of RH Filled


Coupling agent which led to a significant improvement in the filler–matrix interfacial bonding, was still not capable to overcome the main problem of the filler geometry which consequently decreased the impact strength. This situation is normal for particulate fillers and was also reported by Ismail, et al.

(2000) and Mohd Ishak et al.

(1998). The coupling agent probably improved the filler-matrix adhesion by assisting wetting of the fillers surface but did not create chemicals bond. This claim is supported by the evidence from the morphological study later.

4.3.2 Effect of Coupling Agent on Flexural Modulus and Flexural Strength of

RH Filled Impact Modified PVC-U Composites.

97

Figure 4.22 shows the comparison of flexural modulus between composites filled treated and untreated fillers. Incorporation of coupling agent did not show significant improvement in flexural modulus. Flexural modulus improved at 10 phr RH loading by 3% while at 40 phr RH loading increased by 10%. However, flexural modulus decreased at 20 and 30 phr RH by 2 and 4% respectively. As expected, the flexural modulus which indicates material stiffness increased steadily with increasing filler content for all the PVC-U composites. Generally, coupling agents decrease the flexural modulus of the composites especially at higher filler content. However, at 40 phr RH, flexural modulus for composites with coupling agent was higher compared to composites without coupling agent. Incorporation of coupling agents did not allow easier movement of the RH particles within the PVC-U matrix resulting in more flexible composites.

4.5

4

3.5

3

2.5

2

1.5

1

0.5

Sample with Coupling Agent

Sample without Coupling Agent

0

10 20 30 40

RH (phr)

Figure 4.22: The Effect of Coupling Agent on Flexural Modulus of RH Filled


RH filler restricted the polymer chains, thus causes to the higher flexural modules.

98

Applications of LICA 12 did not show any improvement in flexural strength compared to the untreated composites as shown in Figure 4.23. It was found that the flexural strength increased slightly at lower RH content, and decreased gradually at 30 and 40 phr RH content for treated composites. Higher filler content would tend to reduce the plasticising effect of the coupling agent and promotes properties to those hard and brittle materials.

100

80

60

40

20



0

10 20 30 40

RH (phr)

Figure 4.23: The Effect of Coupling Agent on Flexural Strength of RH Filled


4.3.3 Effect of Coupling Agent on the Tensile Strength and Young Modulus of

RH Filled Impact Modified PVC-U Composites.

99

Figure 4.24 shows the relationship between filler loading and tensile strength of

RH filled impact modified PVC-U composites with and without the LICA 12 coupling agent. The importance of the treatment with a coupling agent can be assessed by comparing the results of treated and untreated composites. It is apparent that LICA 12 treatment of rice husk filler has resulted in a decrease in the tensile strength compared to samples without coupling agent. Tensile strength decreases steadily as the loading of

RH increases in the composites. However, the decrement was greater in untreated composites 9 %, than it was in LICA 12 treated composites 8%. The tensile strength for the composites treated with LICA 12 was 23 to 27 % lower compared to the composites without coupling agent.

60

50

40

30

20

10

0

10 20



30

RH (phr)

40

Figure 4.24: The Effect of Coupling Agent on the Tensile Strength of RH Filled


100

A similar effect was reported by Hill and Abdul Khalil (2000), where they found that titanate treatment on coir and oil palm empty fruit bunch (OP-EFB) has resulted in a small decrease in tensile strength. Mohd Ishak et al.

(1998) also reported that the incorporation of coupling agents did not produce any significant effect on the tensile strength. RH that were used in this study was in a particulate form which had an irregular-shaped and had a strong tendency to bundles together. Thus, their capability to support stresses transmitted by the PVC matrix was rather poor, even in the presence of coupling agent. Agglomeration of the filler particles and dewetting of the polymer at the interphase would create stress concentration points. Therefore, decrease the tensile strength of the composites.

Figure 4.25 shows the Young modulus of RH filled impact modified PVC-U composites with and without coupling agent. It is observed that the Young modulus decreases with increasing RH content for composites treated with coupling agents.

Young modulus of composites treated with LICA 12 is generally lower than that of the untreated composites. Colom et al.

(2003) who also studied the effects of treatments on the interface of HDPE/ lignocellulosic fiber composites conclude that this mechanical property depends on the dispersion of the fillers in the polymer matrix, since the lignocellulosic fillers are responsible for the decrease of the deformation capacity within the elastic zone.

101

2

1.5

1

0.5



0

10 20 30 40

RH (phr)

Figure 4.25: The Effect of Coupling Agent on The Young Modulus of RH filled


4.4

Comparison on Mechanical Properties between Rice Husk and Rice Husk

Ash Filled Impact Modified PVC-U Composites

In this section, comparison on mechanical properties between rice husk and rice husk ash filled impact modified PVC-U was evaluated at 20 and 30 phr filler loading.

As shown in Figure 4.26 it is interesting to observe that with similar type of impact modifier, RH filler shows better impact strength compared to RHA filler. At 20 phr

RHA decreases the impact strength by about 32 % while at 30 phr decreases by 50 %

102 compared to RH filler. The different in chemical composition of both RH and RHA may also contribute to the difference in the mechanical properties of the composites.

RHA is produced by thermal degradation (burning process) of rice husk and is accompanied by the removal of the organic fraction. This organic part might be useful in modifying the filler in order to improve the compatibility between polymer matrix and filler, while improving some properties. The silica content of RH is very low about

14 % as reported by Han and Rowell (1997), compared to RHA filler, 96 % (Fuad et al.

1995). Although the polarity both of these fillers makes them capable of forming physical interaction with polar PVC, the interaction is greater for RH fillers compared to RHA. This was due to the higher hydroxyl groups in RH which contribute to the higher dipole-dipole interaction between RH and PVC. The higher silica content in

RHA resulted in of the physical interaction between RHA with polar PVC becoming less effective. As a result, when a composite is subjected to an impact, the ability of RH filled composites to absorb energy during fracture propagation is increased. Therefore, the RH composites resulted in higher impact strength compared to RHA composites.

7

6

5

4

3

Rice Husk

Rice Husk Ash

2

1

0

20

Fillers Content (phr)

30

Figure 4.26: Comparison on Impact Strength between Rice Husk and Rice Husk


103

However, flexural modulus for RHA filled impact modified PVC-U was slightly higher than RH filled acrylic impact modified PVC-U composites (Figure 4.27). This was not surprising since it is well known that the composites with lower impact properties exhibit the stiffest composites. It might be attributed by the detrimental effect of the RHA filler caused by the volume they take up. Even both of these fillers had a similar weight, but the volume of the RHA filler is higher compared to RH. Thus, RHA was able to impart a significant improvement in stiffness compared to RH by hindering the movement of PVC molecules. It was found that at 20 phr, the flexural modulus of

RHA was 20 % higher and with further increased in fillers content 30 phr, the difference became smaller, about 5 %.

3

2.5

2

1.5

1

0.5

0

5

4.5

4

3.5

Rice Husk

Rice Husk Ash

20 30

Filler Content (phr)

Figure 4.27: Comparison on Flexural Modulus between Rice Husk and Rice Husk


Comparison on flexural strength in Figure 4.28 shows that incorporation of RH produced no significant difference between both composites. However, the slight difference could be causes by higher agglomerations of RHA which is higher in volume

104 compared to RH filler. Therefore the ability of RHA fillers in stress transfer decreased and influenced the mechanical properties of the composites.

90

80

70

Rice Husk

Rice Husk Ash

60

50

40

30

20

10

0

20 30


Figure 4.28: Comparison on Flexural Strength between Rice Husk and Rice Husk


The tensile strength result for RH composites was higher compared to RHA composites (Figure 4.29) about 11 %. As reported by Raghi et al.

(2000) in their research on blends of PVC and lignin, they concluded that lignin addition to PVC lead to an increase in tensile strength. The lignin content in RH which is 20 % by weight as reported by Hattotuwa et al.

(2002) might be higher than RHA filler thus resulted in higher tensile strength compared to RHA composites. The greater physical interaction between RH with polar PVC, compared to RHA might also result in higher tensile strength .

105

However, as shown in Figure 4.30 Young modulus of RHA composites exhibited 17 % higher than RH composites. The explanation for Young modulus result is similar to the flexural modulus result.

60

50

40

30

20

Rice Husk

Rice Husk Ash

10

0

20


Figure 4.29: Comparison on Tensile Strength between Rice Husk and Rice Husk


2.5

Rice Husk

Rice Husk Ash 2

1.5

1

0.5

0

Figure 4.30: Comparison on Young Modulus between Rice Husk and Rice Husk


106

4.5

Scanning Electron Microscopy Analysis

Scanning Electron Microscopy (SEM) analysis was employed to obtain some qualitative evidences on the bonding quality between the RH and PVC, the dispersion of RH in the PVC matrix and to correlate between fracture surface and energy absorbed.

Figure 4.31 shows the SEM micrograph of the PVC-U compound sample with impact strength of 4.85 kJ/m 2 . The fracture surface shows a jagged appearance. However, with an incorporation of 10 phr RH a rougher surface is observed compared to PVC-U compound as shown in Figure 4.32 (a). The impact strength decreases to 3.65 kJ/m 2 .

Figures 4.31 and 4.32b to 4.32d clearly show that the fracture surface becomes rough as the filler content increases from 0 to 40 phr.

Figure 4.31:SEM Micrograph of Impact Fracture Surfaces of Unfilled Unmodified

PVC-U

107

The RH filler can be observed by SEM to be distributed unevenly throughout the matrix. Due to hydrogen bonding, this filler had greater tendency to agglomerate. The presence of filler agglomeration is expected to give a detrimental contribution to the impact strength of the PVC-U composites. The impact strength for composites at 20 phr

RH filler decreases to 3.59 kJ/m 2 and further increment in RH filler content at 30 phr, reducesthe impact strength to 3.15 kJ/m 2 . While at 40 phr, the impact strength reduces to 3.05 kJ/m 2 . In other words, the ductile portion contributed by PVC-U matrix is reduced, and the failure mode became more brittle as the RH filler content is increased.

Fillers unlike the matrix are incapable to dissipate stress through the mechanism known as shear yielding prior to fracture. Therefore, the total ability of the material to absorb energy is decreased. Thus, the impact strength tends to decrease with increasing RH filler content. Figure 4.32(a) also shows some holes that indicate the filler pullout. This may be due to poor interfacial bonding between filler and matrix. Further evidence for the poor bonding can be observed from Figures 4.32(b) to 4.32(d).

(a)

Figure 4.32(a): SEM Micrograph of Impact Fracture Surfaces of RH Filled Impact

Modified PVC-U Composites at 10 phr RH Content

108

(b)

Figure 4.32(b): SEM Micrograph of Impact Fracture Surfaces of RH Filled Impact


(c)

Figure 4.32(c): SEM Micrograph of Impact Fracture Surfaces of RH Filled Impact


109

(d)

Figure 4.32(d): SEM Micrograph of Impact Fracture Surfaces of RH Filled Impact


Figure 4.33(a) shows a micrograph of unfilled impact modified PVC-U sample at 8 phr impact modifier content with impact strength 11.14 kJ/m 2 . The fracture surface appearance was different compared to the unmodified unfilled PVC-U. The fracture surface shows the appearance of ductile yielding. While, smooth surface was observed as shown in Figure 4.33(b) for sample at higher impact modifier content of 12 phr with high impact strength, 98.34 kJ/m 2 . The micrograph clearly showed the ductile yielding where high impact energy was absorbed.

110

(a)

Figure 4.33(a): SEM Micrograph of Impact Fracture Surfaces of Unfilled Impact

Modified PVC-U Composites at 8 phr Impact Modifier Content

(b)

Figure 4.33(b): SEM Micrograph of Impact Fracture Surfaces of Unfilled Impact

Modified PVC-U Composites at 12 phr Impact Modifier Content

111

4.6 Thermal Analysis

4.6.1 Thermogravimetry (TGA) Analysis

The thermal stability of natural fibres can be studied by thermogravimetric analysis (TGA). TGA studies were conducted on neat PVC, RH, and RH filled PVC composites. The results of degradation of RH fillers, PVC compound and PVC powder are shown in Figures 4.34 and 4.35, while Table 4.2 shows the degradation temperature of components obtained from TG and DTG curves.

.

As can be seen from Figure 4.35, the RH started degrading at about 200 o C. The peak occured at 305 o C. Degradation of RH showed the lowest degradation temperature as compared to other pure component. Volatilization began at this temperature, and the weight loss was about 35 %. However, it was clearly observed that, another stage at about 100 o C, appeared from the DTG curves. This might be due to the elimination of moisture from the surface of the RH when subjected to heat treatment, as the boiling point and vaporization of water occurred at temperature of 100 o C. The initially undried

RH filler started losing weight as soon as the experiment starts. The weight loss in moisture approximately 6 %. The residue remaining and was subsequently oxidatively combusted and approached 18 % around 500 o C.

112

120

100

80

60

40

PVC Compound

PVC Powder

Rice Husk

20

0

0 200 400 600

Temperature ( o

C)

800 1000

Figure 4.34: TG Curves for PVC Powder, PVC-U Compound and RH Filler

2

0

-2

0 200 400 600 800 1000 1200

-4

-6

-8

-10

-12

-14

Rice Husk

PVC-U Compound

PVC Powder

-16

Temperature ( o

C)

Figu re 4.35: DTG Curves for PVC Powder, PVC-U Compound and RH Filler

113

Table 4.2: Degradation Temperature of Components Obtained from TG and DTG

C urves

PVC

P

-U (powder)

VC-U compound

RH filler

RH 10 phr

RH 20 phr

RH 30 phr

RH 40 phr

T

10%

284.6

294.7

254.8

284.9

274.5

274.8

264.8

Peak 1

2 90

335

305

250

256

253

260

Peak 2

48 5

500

320

305

325

310

Peak 3

490

483

486

495

The thermal degradation of lignocellulosic materials has been reviewed by

G assan and Bledzki, (2001), Okieimen and Eromonsele, (2000). Studies using other natural fibres or fillers to form various composites showed very similar results. As reported by Saheb and Jog, (1999), the thermal degradation of natural fibres occurs in two stages process. The first is in the temperature range of 220-280 o C and the second is in the range of 280-300 o C. They reported that the low temperature degradation process is associated with degradation of hemicellulose whereas the high-temperature process is due to lignin. This thermal degradation of cellulose-based fibers is greatly influenced by their structure and chemical composition and it is well known that, when cellulose based-materials are heated in the range of 100 to 250 o C some of the changes in physical properties of the fibres can be explained in terms of alterations in either physical or chemical structure such as depolymerization, hydrolysis, oxidation, dehydration, decarboxylation and recrystallization (Gassan and Bledzki, 2001). PVC degradation studies are very important because they make it possible to develop processing methods for PVC. The thermal degradation of PVC powder showed two stages of degradation as shown in Figure 4.35. The first step was between 200 o C and 380 o C with a peak at 290 o C, while the second stage occurred at 380-550 o C with a peak at 485 o C. The weight loss of PVC powder at the first stage was about 82 %, while at the second stage of

114 degradation it was approximately 17 %. A carbonaceous residue (10 wt %) with a high carbon content was obtained at the end of the degradation. The degradation temperatures for PVC powder were lower than PVC compound.

As suggested by Okieimen, and Eromonsele (2000), the first step for PVC powder, dehydrochlorination is considered to be the main reaction and HCl is assumed to be th e major volatile product of degradation. Mainly, HCl and benzene and very little alkyl aromatic or condensed ring aromatic hydrocarbons are formed. Alkyl aromatic or condensed ring aromatic hydrocarbons are formed in the second stage of degradation, when very little formation of HCl and benzene are formed. In this stage the polymeric network formed by polyene condensation breaks down in the process of aromatisation of the above C

6

rings (McNeill et al.

1995). Elimination of low molecular hydrocarbon molecules such as benzene, toluene in this stage contribute to the measured weight loss of polymer.

T he thermal degradation temperature for PVC compound showed a higher temperature at 294.7 o C as compared to PVC powder. The initial decomposition temper ature was increased by 10 o C. Thermal stability for PVC compound was improved and this was due to the presence of heat stabilizer. Since, heat is one of the major cause of degradation during processing, with the addition of stabilizers this degradation can be minimized. From the DTG curves (Figure 4.35), two peaks were observed at temperature 335 o C and 500 o C. The weight loss for PVC compound at the first stage is about 34 %, while at the second stages of degradation, it was approximately 76 %. Percentage weight loss of PVC compound in a largely dehydrochlorination phase of the degradation process produced about 18 wt % of residue and this was higher compared to the PVC powder.

115

The results of degradation of RH filled PVC-U composites are shown in Figures

4.36 and 4.37. Three stages of degradation were observed for all composites from 10 to

40 phr RH content. The first peak occurred within temperature range of 250-260 o C.

This peak was associated with the degradation of RH filler. While the second and third peak occurred within the temperature range of 305-325 o C and 483-495 o C respectively.

These peaks were due to the degradation of PVC compound. Initial decomposition temperature decreased with increasing RH loadings. From the results it showed that the incorporation of RH filler did not effect the decomposition of PVC-U matrix.

120

100

80

60

40

PVC/RH 10

PVC/RH 20

PVC/RH 30

PVC/RH 40

20

0

0 200 400 600

Temperature (oC)

800

Figure 4.36: TG Curves for RH Filled PVC-U Composites

1000

116

-2

-3

-4

1

0

-1

0

-7

-8

-9

-5

-6

100 200 300 400 500 600 700

Temperature ( o C)

Figure 4.37: DTG Curves for RH Filled PVC-U Composites

800

PVC/RH 10

PVC/RH 20

PVC/RH 30

PVC/RH 40

900

4 .6.2 Heat Deflection Temperature (HDT)

4 .6.2.1 Effect of RH Content on Heat Deflection Temperature of Impact Modified

PVC-U Composites.

As shown in Figure 4.38, it can be observed that the heat deflection temperature increas es upon adding RH loadings. It is observed that the heat deflection temperature increases slightly with a further increase in RH content from 10 to 20 phr and sudden

117 increase from 20 to 40 phr. The heat deflection temperature is increased by 12% with addition of 40 phr RH content. It has been reported that the incorporation of fillers into highly crystalline polymers generally contributes to an increase in HDT (Schwartz,

1987). However, PVC being an amorphous polymer, with only about 7 – 20 % crystallinity is incapable of undergoing a significant improvement in HDT as the filler content increases.

70

69

68

67

66

65

64

63

62

61

0 10 20

RH Content

30 4 0

Figure 4.38: Effect of RH Content on Heat Deflection Temperature of Impact


118

4.7

Processability Study

4 .7.1 Effect of RH Content Upon Fusion Characteristics of Unmodified PVC-U

Fusion characterisitics such as fusion time, torque at the equilibrium stage (end torque) and fusion temperature, which are obtained from the fusion curve, are used to elucidate the processability of the studied compound. Figure 4.39, shows the fusion curves for PVC compounds which illustrate the changes of viscosity related to torque, temperature and totalized torque versus time. Torque versus time curves were obtained for PVC-U composites at various loadings of fillers. Torque values after 12 minutes running time of the mixture were recorded by the mixer evaluation software.

Figure 4.39: A Typical Temperature Torque Curves of RH filled PVC

Compounds Blended in a Haake Torque Rheometer (starting temperature =

185 o C, rotor speed = 60 rpm)

119

The viscosity-related to torque curve shows two different peaks. The first peak,

A, in th e torque curve was due to loading. The second peak, B, was due to compaction and onset of melting. When PVC sample was loaded into the system, the initial peak was generated, then the torque began to decrease sharply because of free-material flow before compaction, the torque than increased again and generated the second peak. At this peak, B, the material 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, B, are defined as fusion temperature and fusion torque respectively. The time between the loading point A and the fusion point B is defined as fusion time. When the sample was melted and fused for a long time in the mixer, the temperature increased slightly because of more thermal energy absorbed by this sample. The higher temperature resulted in a decrease in the melt viscosity of the sample, therefore the torque decreased as time slowly increased.

Table 4.3 shows that the incorporation of RH decreased the fusion time of unmod ified PVC-U. The fusion time decreased until it reached the minimum duration at 20 phr. With a further increase of another 10 phr no change was observed. However at 40 phr RH content the fusion time increased again. The reason for the fusion time of filled compounds shorter than unfilled compound was the frictional heat generated by the friction of filler-filler and filler-PVC resin particles. The generated frictional heat increased the thermal heat of the filled compounds and allowed PVC resin particles to fuse easily. However, the fusion time of filled compounds increased as the filler content increased due to the increase of separation and slipping among PVC resin particles as the fibre content is increased. As the fine particles mixed into the PVC matrix, dispersion of filler was not perfect. Fine RH particles tend to combine together to form bonded aggregates, which in turn may unite and form as agglomerates. Higher torque may be attributed by agglomeration of fillers. Incorporation of fillers also reduces the mobility of the macromolecular chains of the polymer, thus offering more resistance

(Ahmad Fuad and Salleh Omar, 1994). Therefore, the addition of RH has decreased the fusion time of the PVC compounds. This was also attributed by an increase in frictional

120 heat and shear through the PVC grains as manifested by the torque. The higher temperature resulted in a decrease in a melt viscosity of the sample. End torque that is an indication of the melt viscosity showed a higher value with addition of RH than the

PVC sample. It can be concluded that less thermal energy is needed to be absorbed by

RH filled PVC sample in order for the PVC particle to fuse together.

Table 4.3 : Fusion Characteristics of Unmodified PVC

RH Content Fusion Time End Torque

(phr) (s) (Nm)

0 90.6

13.3

10 79.2 20.6

20

30

40

62.4

62.4

79.2

13.9

14.2

15.6

4 .7.2

Effect of Acrylic Impact Modifier Content Upon Fusion Characteristics of

Unfilled PVC-U

Table 4.4 shows the influence of acrylic impact modifier on the fusion curves of rigid PV C compounds. There was not much changes in fusion time with the addition of

4 phr impact modifier. However, fusion time decreases drastically with increasing acrylic impact modifier content. A similar finding was also reported by Chen et al.

(2001).

121

Table 4.4 : Fusion Characteristics of Modified PVC Blends

Impact Modifier Fusion Time End Torque

Content (phr) (s) (Nm)

0 9 0.6

13.3

4

8

12

90.6

54.6

48

13.4

13.2

14.7

T he acrylic impact modifier which has PMMA outer shell could act as a process ing aid by means of increasing the adhesion property of calcium stearate due to its high compatibility with PVC resin particles. The synergistic lubrication effect between acrylic and calcium stearate enables the PVC resin particles to interact closely.

The acrylic shell is thought to melt first and cause the PVC to become a tacky mass.

The acrylic shell increases the viscosity of the mass, causing a build-up in heat from the processing shear. Thus, increase the transfer of heat and shear throughout the PVC grains. Therefore, the PVC resin particles are binded and allowed to fuse together easily and decreases the fusion time. The processing aid also promoted friction in the system and allowed the fusion process to occur more quickly and uniformly. The higher concentration of acrylic impact modifier, could function as a processing aid and promote PVC particles to fuse together.

4.8

Water Absorption

4.8.1

P ercentage of Water Absorption Upon Impact Modified PVC-U with

Varying RH Content

122

Figure 4.40 shows the relationship between water absorption and filler loading of RH filled impact modified PVC-U samples with varying RH content and impact modifier loading. All curves exhibited a similar pattern. Water absorption for the unfilled unmodified PVC samples showed the lowest value compared to other composites because the matrix polymers are hydrophobic material. The percentage of water absorption increased slightly with increasing RH content.

3

2.5

2

1.5

PVC/RH20/IM4

PVC/RH20/IM12

PVC/RH30/IM8

PVC

PVC/RH20/IM8

PVC/RH10/IM8

PVC/RH40/IM8

1

0.5

0

0 10 20 30 40 50 60 7 0

Days

Figure 4.40: Effect of Water Absorption Upon Impact Modified PVC-U with

Varying RH Content

123

Percentage of water absorption increased about 1.7% from 10 to 40 phr RH loading. No clear equilibrium stage could be observed except for the unfilled u nmodified PVC samples. It is expected that the percentage of water absorption increas ed slowly. RH has greater affinity to water. Increased in a number of micro voids caused by the larger amount of poor bonded area between the hydrophilic filler and the hydrophobic matrix polymer, resulted easily of water absorption (Yang et al.

2005).

RH filled PVC-U samples shows a higher percentage of water absorption compared to

RHA filled PVC-U samples studied by Sivaneswaran (2001). RH is polar and contain more hydroxyl (OH) groups which can form hydrogen bonds with water (H

2

O) molecules. More hydrogen (H

2

) bonding occured between hydroxyl groups and water molecules as the RH loading increased. Therefore, the higher percentage of water absorption were obtained.

The hydrophilic na ture of both natural fibres and fillers also influence the overall mechanical properties, and dimensional variations of the composites.

Mechanism of hydrophilisation tends to increase the equilibrium water uptake through the dev elopment of local and/or overall swelling and plasticisation (or softening) of the matrix. Interfacial decohesion, which induces a degradation of the composite is one of the effect of absorbed water on the physical and mechanical properties of composite

(Bergeret et al.

2001). Comparison between the water absorption of RH filled PVC-U samples with varying impact modifier loading at 20phr RH content resulted in no significant changes.

4.8.2

E ffect of Coupling Agent on Water Absorption Upon Impact Modified

PVC-U

124

Comparis on between LICA 12 treated and untreated composites for sample at

2 0 and 30 phr is shown in Figure 4.41. The composites treated with coupling agent

(C A), showed similar trend result with samples without coupling agent. The composite sample s with LICA 12 showed lower water absorption compared to samples without coupling agent. Water absorption is directly propotional to the filler loadings, and that the coupling agent has a positive effect on the water absorption. The strong interfacial bonding between the filler and matrix polymer caused by the coupling agents limits the water absorption of the composites.

1.2

1

0.8

0.6

0.4

0.2

0

2

1.8

1.6

1.4

0

PVC/RH20/IM8

PVC/IM8/RH20/CA

PVC/RH30/IM8

PVC/IM8/RH30/CA

10 20 30

Days

40 50 60 70

Figure 4.41: Effect of Coupling Agent on Water Absorption Upon Impact

Modified PVC-U

125

The better water resistance of treated modified PVC-U samples may be attributed to the ability of the chemical to form protective layer at the interphase, which prevents the diffusion of water molecules into RH. These results are in agreement with the findings by Sivaneswaran (2002), who proposed the use of titanate coupling agents improved water resistance of RHA filled PVC-U composites. Similar findings was also reported by Yang et al.

(2005) in their research on water absorption behaviour of lignocellulosic filler-polyolefin bio-composites. All filled treated PVC-U samples showed slightly higher percentage of water absorption compared to unfilled unmodified

PVC-U samples. This was due to the present of RH, where it had greater affinity to water.

CHAPTER 5

CONCLUSION

The study has shown that the impact strength of unfilled impact modified PVC-

U composites increased with increasing of acrylic impact modifier content. The flexural modulus decreased with increasing the impact modifier content. However, addition of

20 phr of RH has lowered the impact strength of RH filled impact modified PVC-U at all impact modifier loadings. The incorporation of RH fillers from 10 to 40 phr resulted in the increased of flexural modulus and Young Modulus indicating an improvement in stiffness of unmodified and impact modified PVC-U composites and decreased impact strength, flexural strength and tensile strength of both composites. The agglomerations of the filler and their poor dispersion were responsible to the reduction of these properties. Impact modifier has resulted in enhancing the impact strength at all levels of

RH content. Effectiveness of the impact modifier in enhancing the impact strength decreased with increasing RH content. This shows that the potential use of RH as fillers to enhance the stiffness and reduced cost in PVC-U composites.

127

The effects of accelerated weathering on the impact, flexural and tensile properties of the composites were investigated. Chain scission and polymer crosslinking were the main factors for the deterioration of impact strength and flexural modulus and the slight increase in flexural strength. Water absorption and presence of moisture are believed to be the factors contribute to the increment in impact strength and reduction of the tensile strength and Young Modulus. This explains the variation of the mechanical properties with the weathering period.

RH loading at 20 phr together with LICA 12 coupling agent was found to be most effective in increasing the impact strength of impact modified PVC-U composite.

However, there was not much improvement in flexural and tensile properties.

Comparison between RH and RHA filled impact modified PVC-U composites showed that RH filler resulted in higher impact and tensile strength compared to RHA filler.

While flexural modulus and Young Modulus for RHA composites was higher compared to RH. The different in chemical composition of both fillers such as silica and lignin content may also contribute to the different in mechanical properties of the composites.

RH fillers was found to accelerate the thermal degradation of the composites and the degradation temperature (T

10%

) decreased with increasing RH content. Incorporation of RH fillers did not effect on the decomposition of PVC-U matrix. Meanwhile, heat deflection temperature increased with further increase of RH content. Fusion time of unmodified PVC-U compounds decreased with increasing RH loadings. Similar result was obtained where fusion time decrease with increasing impact modifier loading.

The percentage of water absorption increased slightly with increasing RH content. Water absorption increased as the impact modifier loading decreased. All treated samples exhibited lower percentage of water absorption compared to the

128 untreated samples. The SEM micrograph which showed yielding had high impact values compared to low impact value which showed jagged appearances. The RH fillers which distributed unevenly throughout the matrix could also be observed by SEM.

Based on the results, RH has good potential to be utilized as fillers in PVC-U.

The optimum composition which gives balance of properties based on stiffness and toughness of PVC-U composites is PVC-U at 8 phr of acrylic impact modifier and 20 phr of RH treated with LICA 12.

5.2 Suggestions For Further Work i. Samples preparation in this study was prepared by using two-roll mill and hot press. It would be interesting to study the effect of processing conditions for twin screw extruder which are normally used for production, such as screw speed and barrel temperature on fusion and mechanical properties of the PVC-U composites. ii. It is suggested to investigate the effect of RH particle size on the mechanical properties of impact-modified PVC-U.

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