World Journal Of Engineering
PRESSURE-VOLUME-TEMPERATURE CHARACTERISTIC OF GLYCEROL
PLASTICIZED POLYVINYL ALCOHOL AND CASSAVA STARCH BLENDS
Low Chong-Yu, Lee Tin-Sin
Department of Chemical Engineering, Faculty of Engineering & Science, Universiti Tunku Abdul
Rahman, Jalan Genting Kelang, 53300 Setapak, Kuala Lumpur, Malaysia
While phosphoric acid acted as heat stabilizer to
prevent occurrence of pre-processing thermal
degradation. The mixtures were then compounded
using a twin screws co-rotating extruder to produce
plasticized PVOH (PPV). The composition of PPV is
shown in Table 1. All heating zones were set at 160 oC
while the screw speed was set at 250 rpm. After that,
PPV, CSS and glycerol were mixed again in a high
speed mixer as PPV-CSS mixtures at the composition
shown in Table 2. The mixtures were compounded
again in similar twin screws co-rotating extruder. All
heating zones were set at 140 oC. Then, the extruded
compounds were palletized and immediately sealed in
polyethylene bags.
Introduction
The continual depletion of landfill space and
environmental pollution of non-degradable or
partially degradable petroleum based polymers
have led the scientists to develop alternatives
polymers compound based on agricultural
resources. Starch as one of the cheapest and
available abundantly agricultural resource is a
good choice to blend with polymers for
improvement of biodegradability while lowering
the cost of the polymer compounds. In this study,
cassava starch (CSS) is blended with polyvinyl
alcohol (PVOH). PVOH is a biodegradable type
of polymer possesses high polarity due to the
existing of hydroxyl functional groups (-OH).
Previous papers [1,2] have reported that the
blending of starch and PVOH is highly
compatible due to the presence of hydrogen
bonding between the hydroxyl groups of starch
and PVOH. The objective of the presence study
is to characterize the pressure-volumetemperature (PVT) characteristic of PVOHcassava starch compound. PVT is able to provide
the crystallinity and compressibility information
of polymer compound subsequently leads to the
estimation of shrinkage in injection moulded
articles.
Thermal transition measurement
The specific volumes of the polymers as a
function of temperature at 200 bars to 2000 bars were
measured by pressure-volume-temperature (PVT)
apparatus- SWO pvT 100. Initially, the known amount
of specimen was filled into the cylindrical test cell
with the piston inserted. Hydraulic pressure was
applied to the specimens via the piston with an inert
polytetrafluoroethylene (PTFE) seal to avoid potential
leakage of molten specimen during testing. After precompression, the sample was heated in the test cell
until equilibrates at the desired temperature of 200 oC
for 5 minutes. The tests were conducted at low cooling
rate of 5 oC/min to ensure sufficiently uniform
temperature distribution within the specimen. The
position of the piston was recorded continuously with
decreasing temperatures. Finally, the specific volumes
were calculated and plotted as a function of
temperature as shown in Fig. 1.
Experimental
Materials
Fully hydrolysed PVOH grade BF-17H
(viscosity 25-30 cps, hydrolysis 99.4-99.8
mole %, ash < 0.7 %) was supplied by Chang
Chung Petrochemical Co., Ltd.. CSS was
obtained from Thailand- Cap Kapal ABC.
Glycerol (C3H8O3) at 99.5 % purity was
purchased from Fisher Scientific. Calcium
stearate was provided by Sun Ace Kakoh Sdn.
Bhd. and phosphoric acid at 85% purity was
obtained from Merck. All materials were used as
received.
Table 1 Compositions of glycerol plasticized PVOH (PPV)
Specimen Glycerol PVOH
CaS
Phosporic
(phr)
(%)
(phr)
acid (g)
PPV
40
100
2
4.18
Table 2 Compositions of PPV blending with CSS
Specimen
PPV
CSS
Glycerol
(wt %)
(wt %)
(phr)
PPVCSS
40
60
20
Specimens Preparation
PVOH, glycerol, calcium stearate (CaS), and
phosphoric acid were physically mixed in a high
speed mixer for 15 minutes. Glycerol and CaS
were used as plasticizer and internal lubricant.
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World Journal Of Engineering
morphology in PPV where different molecular sizes
and structures of starch and PVOH have disrupted the
crystallinity morphology. Starch is denser than PVOH
due to high branched of amylopectin structures resist
the mobility of polymer chains and promote formation
substantial amount of hydrogen bonds [5]. CSS is
among the starch that has been found to possess semicrystalline long-branched structures [5]. Furthermore,
the transition of onset melting points of PPV and
PVOH-starch as identified at line A-B showed an
agreement with previous DSC study that onset melting
points were detected at the range of 160-180 oC [6].
Incorporation of starch has eliminated the crystalline
content of PPV to an extent approaching the behaviour
of amorphous polymer. In short, PVOH has
significantly changed the processing behaviour of
starch by influencing the blending morphology and
interactions. PPV-starch compounds are preferable to
be melt processed at temperature > 180 oC in order to
achieve absolute molten state. The amorphous
structure of starch filled PVOH has lower changes of
specific volume subsequently leads to lower in
shrinkage when injection moulded.
Results and Discussion
Fig.1 shows PVT diagram of PPV and
PPVCSS measurements at pressure 200-2000 bar.
As expected, when the pressure increased, the
specific volume reduced gradually. This is
because higher pressures have compressed the
samples. Meanwhile, the PVT outcomes of PPV
showed within the range 0.75-0.84 of neat PVOH
as reported by Zoller and Walsh [3]. However,
the extent decrements of PPV’s specific volume
at decreasing temperature were lower than neat
PVOH. This condition is obviously visible at
molten state (above line A-B). Addition of
glycerol as plasticizer has disrupted the
crystallinity of neat PVOH. Glycerol has acted as
external disturbance which disrupts the PVOH
molecular chains to rearrange in compact
structure. Hence, the amorphous structure in PPV
reduced the changes of specific volume during
cooling process.
A
Specific volume, v (cm3/g)
0.84
Conclusion
0.82
200 bar
0.80
500 bar
Blending of CSS has reduced the crystallinity of
the PPV by lowering the transition of specific volumes
at melting stage and further rendering lower shrinkage
when injection moulded.
800 bar
0.78
1000 bar
1200 bar
B
0.76
1500 bar
2000 bar
0.74
0.72
20
40
60
80
100
120
140
160
180
200
References
220
Temperature, T (oC)
1. Lee, T. S., Rahman, W. A. W. A., Rahmat, A. R.,
and Samad, A. A. (2010). Computational modeling
and experimental infrared spectroscopy of hydrogen
bonding interactions in polyvinyl alcohol-starch
blends. Polymer. 51, 1206-1211.
2. Lee, T. S., Rahman, W. A. W. A., Rahmat, A. R.,
and Khan, M. I. (2010). Detection of synergistic
interactions of polyvinyl alcohol-cassava starch
blends through DSC. Carbohydrate Polym.. 79(1),
224-226.
3. Zoller, P. ang Walsh, D. (1995). Standard PressureVolume-Temperature Data for Polymers. USA:
CRC Press.
4. Abbès, B., Ayad, R., Pruhdommed, J. C., and
Onteniente, J. P. (1998). Numerical Simulation of
Thermoplastic Wheat Starch Injection Molding
Process. Polym. Eng. Sci.. 38 (12), 2029-2038.
5. Liu, J., Xie, F., Yu, L., Chen, J., and Li, L. (2009).
Thermal processing of starch-based polymer. Prog.
Polym. Sci.. 34, 1348-1368.
6. Salleh, M. S. N., Rahman, W. A. W. A., and Lee, T.
S. (2009). Tensile behaviour and thermal analysis of
biodegradable injection grade tapioca starch filled
plastic poly(vinyl alcohol). Proc. Env. Sci. & Tech.
Conference
(ESTEC2009).
7-8
December.
Terengganu- Malaysia, 485-493.
(a)
0.78
Specific volume, v (cm3/g)
0.77
A
0.76
200 bar
0.75
500 bar
0.74
800 bar
0.73
1000 bar
1200 bar
0.72
1500 bar
B
0.71
2000 bar
0.70
0.69
0.68
20
40
60
80
100
120
140
160
180
200
220
Temperature, T (oC)
(b)
Fig.1 PVT diagrams of (a) PPV and (b) PPVCSS
Generally, it was found that addition of
starch also disrupted the crystallinity of PVOH.
The thermal transition state at line A-B declined
at high starch contains. This indicated that
blending different molecule structure- i.e. starch
into PVOH has deteriorated the crystal
rearrangement during cooling process. High
amount of starch in PPV caused the entire
blending transformed into amorphous phase. This
outcome agrees with previous study conducted by
Abbes et al. [4] that thermoplastic starch is not
very compressive with obvious thermal transition
only found at 0.1 and 40 MPa PVT tests. This is
due to the incorporation of starch has affected the
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