Accepted Manuscript Title: Effect of Different Polyol-Based Plasticizers on Thermal Properties of Polyvinyl Alcohol (PVA):Starch Blends Films Author: Ahmet Alper Aydın Vladimir Ilberg PII: DOI: Reference:
S0144-8617(15)00841-3 http://dx.doi.org/doi:10.1016/j.carbpol.2015.08.093 CARP 10296
To appear in: Received date: Revised date: Accepted date:
20-5-2015 12-8-2015 29-8-2015
Please cite this article as: Aydin, A. A., and Ilberg, V.,Effect of Different Polyol-Based Plasticizers on Thermal Properties of Polyvinyl Alcohol (PVA):Starch Blends Films, Carbohydrate Polymers
(2015), http://dx.doi.org/10.1016/j.carbpol.2015.08.093 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Different Polyol-Based Plasticizers on Thermal Properties of Polyvinyl Alcohol
(PVA):Starch Blends Films
Ahmet Alper Aydın1,* and Vladimir Ilberg2
Istanbul Technical University, 34469 Maslak, Istanbul, Turkey. Email: [email protected]
Triesdorf, Am Staudengarten 11, D-85350, Freising, Germany.
A series of gelatinized polyvinyl alcohol (PVA):starch blends were prepared with various polyol-
based plasticizers in 5 wt%, 15 wt% and 25 wt% ratios via solution casting method. The obtained
films were analyzed by Fourier transform infrared (FT-IR) spectroscopy, differential scanning
calorimetry (DSC) and thermogravimetric analysis (TGA). Remarkable changes have been
observed in glass-transition temperature (Tg) and thermal stability of the samples containing
varying concentrations of different plasticizers and they have been discussed in detail with
respect to the conducted thermal and chemical analyses. The observed order of Tg point
depression of the samples with containing 15 wt% plasticizer content is 1,4-butanediol - 1,2,6-
hexanetriol - pentaerythriyol - xylitol - mannitol, which is similar to the sequence of the thermal
stability changes of the samples. In the presence of 25 wt % 1,4-butanediol, the Tg point of
PVA:starch films reduce from 76.1oC to 37.2oC.
Keywords: starch; polyvinyl alcohol; plasticizer; polyol; thermal properties; glass transition
Chemical compounds studied in this article: Corn Starch (PubChem CID: 24836924);
Polyvinyl Alcohol (PubChem CID: 11119); 1,4-Butanediol (PubChem CID: 8064); 1,2,6-
Hexanetriol (PubChem CID: 7823); Pentaerythritol (PubChem CID: 8285); Xylitol (PubChem
CID: 6912); Mannitol (PubChem CID: 6251)
Chemical Engineering Department, Faculty of Chemical and Metallurgical Engineering,
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Faculty of Gardening and Food Technology, University of Applied Sciences Weihenstephan-
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Petroleum-based synthetic polymers with high molecular weight and hydrophobic character have
been extensively used in different areas. However, their extensive use and ecological concerns
have increased interest in biodegradable alternatives from renewable sources (Petersen et al.,
1999; Weber et al., 2002).However, these polymers show very high chemical stability and
degrade very slowly in the environment. In the 21st century, environmental and health issues
associated with disposal and recycling of these products indicate major problems and extensive
research activities continue for developing their biodegradable alternatives.
There have been intensive attempts to develop biodegradable plastics with the purpose of
protecting the environment. Biodegradable polymers offer environmentally friendly substitutes
which can be degraded by microorganisms in soil or water. The approaches toward development
of biodegradable polymers contain modification of non-degradable polymers by introducing
degradable linkages or blending biodegradable polymers and tailoring their formulations so that
the resulting materials have properties superior to the individual components (Tang, & Alavi,
Starch has been considered as one of the most suitable materials among natural biopolymers due
to its low cost and abundant availability (Wang, Chang, &Zhang, 2010; Gross & Kalra, 2002).
Polysaccharides such as starch, chitosan and cellulose are typical examples of natural
biodegradable polymers with relatively good biocompatibility. However, starch-based products
exhibit several disadvantages such as brittleness, strong hydrophilic character, poor mechanical
properties and processability which limit their applications in material engineering. Therefore, the
weakness of starch products must be compensated by blending starch with other synthesized
degradable polymers (Shi et al., 2008). In this sense, blends with PVA are well suited to improve
the strength and flexibility of starch-based products as a result of chemical resistance, optical and
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physical properties, good film-forming capability, water solubility and biocompatibility of PVA
(Nakayama, Takatsuka, & Matsuda, 1999; Cinelli, Chiellini, Gordon, & Chiellini, 2005). the
making biodegradable blends with natural polymers due to its good physical properties, film-
forming capability and water solubility
Although PVA is a suitable solution to improve the properties of starch-based products, further
improvement is still needed. As a result of the formed hydrogen bonds between PVA and starch
molecules, the molecular movement and processability of the blend are restrained. At this point,
plasticizers play an important role to reduce the strong interactions between PVA and starch
molecules by forming new hydrogen bonds with PVA and starch. In this way, PVA:starch blends
are processed into mouldable thermoplastic materials in the presence of suitable plasticizers
(Chin & Te, 2008; Forssell et al., 1997; Raj, Siddaramaiah & Somashekar, 2004). Besides, the
polarity of PVA increases the hydrolytic attack to the blend by atmospheric moisture and
accelerates the break down in sugar molecules (Raj, Siddaramaiah, & Somashekar, 2004). Since
starch and PVA molecules contain many hydroxyl groups, their blend films also have hydrophilic
nature. Therefore, their thermal and mechanical properties and water resistance must be improved
and tailored for different applications.
Although PVA:starch blend films have been produced by means of solution casting, it is not an
economic and efficient way compared to thermoplastic processing in larger production scale.
Glass-transition temperature (Tg) plays an important role in production of thermoplastic products
via extrusion. At the Tg point, the cohesive forces drastically decrease and the polymer expands.
The increase in free volume reaches an extent that there is room for migration of segments, which
provides flow of the polymer. Addition of plasticizers reduces molecular interactions, lowers the
Tg point and makes the polymer more rubber-like.
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The degree of conversion of PVA:starch blend into mouldable thermoplastic is a measure of Tg
point depression of the sample. The cohesive forces drastically decrease at the Tg point and the
polymer expands to create room for migration of segments, which provides flow of the polymer.
In the case of PVA and starch, strong molecular interactions are disturbed in the presence of
plasticizers and the Tg point is reduced which makes the polymer more rubber-like (Jayasekara et
al., 2003; Yoon, Chough, & Park, 2006a; Sreedhar et al., 2006).
Different plasticizers like glycerol (Sreekumar, Al-Harthi, & De, 2012; Luo, Li, & Lin, 2012),
polyethylene glycol (Sreedhar et al., 2005), sorbitol (Arvanitoyannis, Kolokuris, Nakayama,
Yamamoto, & Aiba, 1997), sucrose (Arvanitoyannis, Kolokuris, Nakayama, Yamamoto, & Aiba,
1997), urea (Luo, Li, & Lin, 2012), ascorbic acid (Yoon, 2014), citric acid (Shi et al., 2008;
Yoon, Chough, & Park, 2006a), succinic acid (Yoon, Chough, & Park, 2006b), malic acid (Yoon,
Chough, & Park, 2006b), tartaric acid (Yoon, Chough, & Park, 2006b) or more complex
plasticizers (Zhou, Cu, Jia, & Xie, 2009) have been successfully employed to improve flexibility
of the blends.
Liu et al. (1999) compounded glycerol and water with PVA:starch blend in a single screw
extruder. They reported that glycerol was much more effective than water as a plasticizer. In
addition, Park et al. (2005) examined glycerol, sorbitol and citric acid as additives with different
functional groups. They concluded that due to the increased hydrogen bonding in the presence of
both hydroxyl group and carboxyl group, citric acid provided better film forming compared to
sorbitol and glycerol. Similarly, Shi et al. (2008) reported another role of citric acid in the blend.
According to their reported data, partial esterification takes place between starch (or PVA) and
citric acid during processing at 140oC in the extruder. While partial esterification initially
increases the tensile strength and Tg of the blend in the presence of 5% citric acid, further
increase in residual citric acid amount provides plasticizing effect.
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Other effective ways of improving the properties of PVA:starch blends include: (i) chemically
modifying starch or PVA (Kim, & Lee, 2002; Kim, 2003), (ii) physically modifying by forming
PVA/starch based nanocomposites (Dean, Do, Petinakis, Yu, 2008; Majdzadeh-Ardakani, &
Nazari, 2010; Vasile et al., 2008; Tang, Alavi, & Herald, 2008), (iii) chemically modifying the
PVA and starch during or after blending process with crosslinking agents such as boric acid (Yin,
Li, Liu, & Li, 2005), borax (Sreedhar et al., 2005), epichlorohydrin (Sreedhar et al., 2006) and
hexamethoxymethylmelamine (Chen et al., 1997).
The aim of this paper is to introduce the influence of different polyol-based plasticizers on
plasticization of neat PVA:starch blend with respect to the Tg point depression and thermal
stability changes in the presence of plasticizers. For this purpose, 1,4-butanediol, 1,2,6-
hexanetriol, pentaerythritol, xylitol and D-mannitol have been investigated as polyol-based new
plasticizers and the changes in Tg point and thermal stability of the blends containing varying
amounts of plasticizers have been discussed in detail with respect to the conducted thermal and
2. Materials and Methods
Corn starch was supplied by Sigma-Aldrich and it was composed of 73% amylopectin and 27%
amylose. PVA was also obtained from Sigma-Aldrich, which was 99% hydrolyzed with an
average molecular weight of 130.000 amu.
The conducted strategy in choosing plasticizer was based on obtaining a series compounds with
varying hydroxyl group functionality on the carbon chain. In this manner, the series of 1,4-
butanediol (99%, Sigma), 1,2,6-hexanetriol (96%, Sigma), pentaerythritol (>99%, Sigma), xylitol
(>99%, Sigma) and D-mannitol (>98%, Sigma), which contains polyols with different number of
hydroxyl groups as shown in Fig. 1, was used as received from the supplier.
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ip t cr us
Fig. 1. Chemical structures of the investigated plasticizers
2.2 Preparation of PVA:Starch blend films
PVA:starch (1:1, w/w) blend film samples were prepared by solution casting method according to
the mass ratios given in Table 1. First, PVA was dissolved in 300 mL hot water at 97±2oC. After
complete dissolution of PVA, calculated amount of plasticizer was added and stirred for 15
minutes in order to maintain homogeneous distribution of plasticizer in hot water. Afterwards,
dispersed starch in 100 mL water was added and the mixture was stirred for another 45 minutes.
The mixtures were then casted onto petri dishes with similar weight (30 ± 2 g) and dried at 65oC
to constant weight. In order to comparatively investigate the blends, Samples containing neat
corn starch and PVA:starch were also prepared as reference.
The peeled film samples were directly taken into sealed plastic bags and stored at room
temperature in desiccator containing fresh silica-gel beads to maintain constant low-humidity.
Samples exceeding 2 days were withdrawn and prepared again to guarantee low humidity of the
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Table 1. Abbreviations and corresponding sample compositions
PSG-M5 PSG-M15 PSG-M25 Abbreviation PSG-P5 PSG-P15
PSG-H5 PSG-H15 PSG-H25
(wt% of the dry weight)
5 15 25 Pentaerythritol
Abbreviation PSG-X5 PSG-X15 PSG-X25
(wt% of the dry weight)
1,2,6-Hexanetriol (wt% of the dry weight)
5 15 25 Xylitol
5 15 25 Mannitol
(wt% of the dry weight)
PSG-B5 PSG-B15 PSG-B25
1,4-Butanediol (wt% of the dry weight)
5 15 25
2.3 Fourier transform infrared spectroscopy (FT-IR)
FT-IR spectra of the synthesized high-chain fatty acid esters were recorded on a Perkin Elmer
FT-IR Spectrum 100 spectrometer with universal ATR accessory between 4000 and 650 cm-1
2.4 Differential scanning calorimeter (DSC)
A TA Instruments Q200 DSC was used for the calorimeter analyses of the samples. The
measurements were carried out under inert nitrogen atmosphere at 50 ml/min flow rate. All the
DSC thermal analyses were conducted at 5oC/min rate for the determination of glass transition
DSC analyses were conducted according to the ASTM standard test methods with designation
numbers E 793-06 and E 1269-11, explaining the determination of enthalpies of fusion and
freezing and specific heat of liquids and solids, respectively. The temperature and heat
calibrations of the instrument were systematically performed with sapphire and indium references
prior to the analyses on each workday.
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Every presented DSC data in this paper is calculated according to the results of at least 3
individual analyses in order to minimize the uncertainty.
2.5 Thermo-gravimetric analyses (TGA)
A NETZSCH STA 409 PC/PG was used for determination of thermo-gravimetric decomposition
of the film samples, including decomposition behavior, onset temperature and weight losses at
different temperatures of the samples. The analyses were carried out under inert argon
atmosphere at 60 ml/min flow and 10oC/min heating rate between 30 and 600oC.
The analyses were conducted according to the general principles given in BS EN ISO
11358:1997. The weight and temperature calibrations of the instrument were made using the
reference weight and according to the sensor calibration of the instrument, respectively. The
calibration of the instrument was performed systematically prior to the first analysis of each
Every presented TGA data in this paper is calculated according to the results of at least 2
3. Results and Discussion
3.1 Plasticizers and hydrogen bonding (FT-IR)
The hydrogen bonding plays an important role in formation of strong interactions between starch,
PVA and plasticizer molecules and the FT-IR spectra enable the interactions to be identified. The
changes in peak bandwidth, strength and frequency provide valuable data for interpretations on
the formation of intermolecular hydrogen bonding in the samples.
In general, the changes in band formations are clearly seen in the overlapped spectra of the blends
given in Fig. 2(ii) compared to the polyol-based plasticizers in Fig. 2(i). In Fig. 2(ii)-a, the broad
transmittance band of starch at 3293 cm-1 is assigned to the stretching vibration of –OH and the
band at 2922 cm-1 is due to C–H stretching in the molecule. The band peak at 1638 cm-1 indicates
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the bound water in starch with the formed hydrogen bonds. The bands located at 1411 cm-1 and
858 cm-1 are assigned to the vibrations associated with the CH2 group. The peak at 1011 cm-1 is
related to C–O bond stretching of C–O–C groups in anhydroglucose ring. The C–O bond
stretching of C–O–H group is seen at 1150 cm-1. The given data are in good agreement with the
literature (Fang et al., 2002; Pavlovic & Brandao, 2003; Ma & Yu, 2004).
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183 184 185 186
Fig. 2. FTIR spectra: i – (a) 1,4-Butanediol, (b) 1,2,6-Hexanetriol, (c) Pentaerythritol, (d) Xylitol, (e) Mannitol; ii – (a) Starch, (b) PVA:Starch, (c) PSG-B15, (d) PSG-H15, (e) PSG-P15, (f) PSG-X15, (g) PSG-M15
187 9 Page 9 of 24
The hydrogen bonding between –OH groups of starch, PVA and polyol-based plasticizers in the
blends shifts the –OH stretching vibration bands of all neat polyol-based plasticizers to lower
frequency region by around 4-14 cm-1 and the corresponding bands of blends get broader and
stronger. Additionally, the positions of the C–O stretching bands of the C–O–H group located at
around 1150 cm-1 significantly shift to lower frequencies as a result of the changed hydrogen
bonding ratio in the blends. The single C–O stretching band of the C–O–C group in starch and
PVA:starch samples transforms into double peak with the added plasticizers. The bound H2O
shifts from 1638 cm-1 to higher frequencies by the addition of PVA and polyol-based plasticizers,
indicating that the water molecules are more strongly hydrogen bonded in the presence of PVA
and plasticizers (Wolkers et al., 2004). The details of the FT-IR spectra given in Fig. 2(ii) are
tabulated in Table 2.
Table 2 indicates that comparative changes are observed between spectra of polyol-based
plasticizer containing samples and neat starch and PVA:starch samples, whereas spectra of
plasticizer containing samples have generally close band frequencies as a result of their similar
chemical structures. In PSG-X15 and PSG-M15 samples, C-H stretching is cleaved into two
bands at around 2937-2932 and 2908-2910 cm-1. Besides, C-O stretching of C-O-C is located at
higher frequencies compared to other polyol-based plasticizer containing samples.
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Table 2. Summary of FT-IR results PSGB15 (cm-1)
OH stretching C-H streching Bound water Vibrations associated to CH2 group C-O stretching of C-O-C C-O stretching of C-O-H
3.2 The effects of plasticizers on thermal properties
3.2.1 DSC analyses and changes in Tg points
As it is given in Table 3 and Fig. 3-i, the casted sample of pure PVA has a clear Tg at 70.5oC.
However, such a clear Tg cannot be observed for gelatinized starch, which could be because of its
amorphous and hygroscopic nature. It has been stated in literature that the absence of its Tg may
be due to amorphous chains surrounded by crystalline domains, presence of moisture, physical
crosslinks inhibiting the movements of the amorphous chain segments or presence of
intercrystalline phases (Sreedhar et al., 2005; Shi et al., 2008). Although there are no discernible
changes in the DSC thermogram of gelatinized starch film, the PVA:starch (1:1, w/w) blend has a
clear Tg at 76.1oC, which is higher than that of neat PVA as a result of the hydrogen bonding
interactions between starch and PVA.
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Table 3. Glass transition points (Tg) of the samples with 95% confidence interval Abbreviation PVA:Starch PSG-H5 PSG-H15 PSG-H25 PSG-M5 PSG-M15 PSG-M25
Tg (oC) ± 95% Conf. Int. 76.1 ± 1.4 49.9 ± 0.6 45.6 ± 1.2 43.0 ± 2.3 52.5 ± 1.3 52.2 ± 0.4 51.6 ± 0.4
Tg (oC) ± 95% Conf. Int. 70.5 ± 1.2 49.2 ± 1.7 45.2 ± 0.5 37.2 ± 2.2 51.5 ± 0.1 51.4 ± 1.8 46.6 ± 0.4 54.1 ± 0.2 48.7 ± 1.8
Abbreviation PVA PSG-B5 PSG-B15 PSG-B25 PSG-X5 PSG-X15 PSG-X25 PSG-P5 PSG-P15
Plasticizers are low molecular weight substances, which reduce the Tg point of polymers and
provide their flow by improving flexibility and processability. In this sense, the effects of
plasticizers in different polymer blend compositions can be observed by investigating the degree
of changes in Tg points at different concentrations (Jayasekara et al., 2003; Yoon, Chough, &
Park, 2006a; Sreedhar et al., 2006).
In the case of PVA:starch films, two types of hydrogen bonding interactions take place: (1)
hydrogen bonding between hydroxyl groups of PVA and gelatinized starch and (2) hydrogen
bonding between functional groups of PVA, starch and plasticizer. In the second type,
plasticizers function as agents penetrating the matrix and interrupting the hydrogen bonding
sequence between PVA and starch. They form hydrogen bonding bridges via functional groups in
their chemical structure and spread throughout the matrix with their small molecular size and low
molecular weight. In this way, polar attractive forces are established between the plasticizer and
chain segments, which are responsible for the reduction of Tg point and simultaneously,
enhancement of chain segment mobility with better flexibility and processibility of the matrix
(Chin & Te, 2008; Forssell et al., 1997; Raj, Siddaramaiah, & Somashekar, 2004).
The hydroxyl groups are hydrogen bonding quarters on the investigated plasticizers (Fig. 1)
which might possibly form new hydrogen bonding bridges and enable better segment mobility in
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the PVA:starch matrix. In this way, 5 wt% addition of these plasticizers into PVA:starch blend
significantly drops the Tg point in Table 3. The Tg points shift significantly to lower temperature
region in DSC data presented in Fig. 3.
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Fig. 3. DSC data: i – (a) Starch, (b) PVOH, (c) Starch:PVOH; ii – (a) PSG-B5, (b) PSG-H5, (c) PSG-P5, (d) PSG-X5, (e) PSG-M5; iii – (a) PSG-B15, (b) PSG-H15, (c) PSG-P15, (d) PSG-X15, (e) PSG-M15; iv – (a) PSG-B25, (b) PSG-H25, (c) PSG-X25, (d) PSG-M25
Unlike xylitol and mannitol, the Tg points continue decreasing in the presence of 15 wt% and 25
wt% 1,4-butanediol, 1,2,6-hexanetriol and pentaerythritol as a result of increasing number of
available hydroxyl groups. However, Tg points do not significantly decrease in the samples
containing 15 wt% xylitol and mannitol. Only for xylitol, increase in its mass ratio to 25 wt%
leads to additional increase in segment mobility and decrease in Tg point down to 46.6oC.
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The observed different plasticizing efficiencies of xylitol and mannitol can be attributed to their
molecular structures. Compared to 1,4-butanediol, 1,2,6-hexanetriol and pentaerythritol, they are
relatively larger molecules with 5 and 6 hydroxyl groups, respectively. Probably, further
penetration into chain segments of PVA and starch is prevented due to their larger molecular
geometry after the initial plasticization of 5 wt% addition. Consequently, it can be mentioned that
mannitol molecules tend to interact with each other and do not significantly improve the thermal
properties of the blend, whereas smaller xylitol molecules can further play role in plasticization
when they are found in high amount.
3.2.2 Thermal-decomposition behaviors and thermogravimetric analyses
In the given figures, three distinct regions of mass loss can be seen. There are generally three
distinct mass loss regions in PVA:starch samples reported in literature. The first region (between
75oC and 200oC) is attributed to the loss of loosely bound water, accompanied by the formation
of volatile disintegrated products such as dislocation of the plasticizers in the blend. The second
region is described as the main decomposition step and the final stage is the carbonization of the
organic matter (above 500oC) (Galdeno et al., 2009; Luo, X., Li, J., & Lin, X, 2012; Saiah et al.,
2009; Shi et al., 2011). The thermal decomposition behaviors of various PVA:starch films
with/without polyol-based plasticizers are given in Fig. 4.
In addition to the overlapped thermal decomposition curves in Fig. 4, the thermal decomposition
data are also tabulated in Table 4 to present the 10 % weight loss temperature and residual
weights at 300oC, 400oC and 500oC for reference samples (starch, PVA, PVA:starch) and 15 wt%
polyol-based plasticizer containing samples.
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Table 4. Thermal decomposition values of the samples with 15 wt% plasticizer Residual weight percentage at 400oC
88.84 52.12 80.32 72.22 68.11 74.55 74.87 89.47
21.82 27.99 33.16 28.17 24.69 26.72 23.88 30.85
16.61 10.54 20.85 14.09 11.79 11.37 11.52 14.27
at 300 C
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Starch PVA PVA:Starch PSG-B15 PSG-H15 PSG-P15 PSG-X15 PSG-M15
Temperature at 10 % weight loss 298.4oC 258.8oC 285.6oC 244.9oC 238.3oC 269.4oC 275.2oC 298.7oC
281 282 283
Fig. 4. TGA data: i – (a) Starch, (b) PVOH and (c) Starch:PVOH; ii – (a) PSG-B15, (b) PSGH15, (c) PSG-M15, (d) PSG-P15, (e) PSG-X15 15 Page 15 of 24
The PVA:starch films show better thermal stability than neat PVA as a result of the thermal
resistive cyclic hemiacetal in starch structure and development of blending towards high-energy
stability of the mixture (Sin et al., 2011). Therefore, PVA:starch sample has closer 10 %
decomposition temperature to gelatinized neat starch instead of PVA and less weight loss than
neat PVA at 300oC, 400oC and 500oC compared to PVA.
When the thermal decomposition data of polyol-based plasticizer containing samples are
examined, reductions in thermal resistivity are generally observed, except for mannitol containing
sample, compared to the PVA:starch sample. Although the mass loss order of different
plasticizers is attributed to their volatility difference in literature (Ma, Yu, & Wan, 2006), the
mass loss order of samples containing different plasticizers is also related to intermolecular
interactions and mobility between the plasticizer, PVA and starch chains according to the
interpreted data below.
As PVA:starch sample has closer thermal stability to starch due to the development of blending
towards high-energy stability, it is expected that higher the plasticization effect, lower the thermal
stability of the blend sample.
Other than the exception of 1,4-butanediol and 1,2,6-hexanetriol containing samples, the
increasing hydroxyl number and molecular size of the plasticizer enhance the thermal stability
with a maximum in the presence of mannitol. Although the increase in molecular size of the
plasticizers decreases their penetration ability into PVA and starch chain segments and limit the
Tg depletion (plasticization effect), it provides convergence of the thermal decomposition
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resistance of the blend samples to neat PVA:starch film as a result of the developed blending with
high-energy stability. The exceptional behavior of 1,4-butanediol and 1,2,6-hexanetriol
containing samples might be attributed to their volatility difference. Therefore, the thermal
stability of PVA:starch:plasticizer samples is related to not only the volatility difference of the
plasticizers, but also to the mobility between the plasticizer, PVA and starch chains.
The mannitol containing sample shows better thermal endurance than neat starch and PVA:starch
samples at 300 oC and its 10 % weight loss temperature is at 298.7 oC, which is the highest
among the analyzed samples. However, its decomposition rate later gets higher and at 400oC and
500oC, the neat PVA:starch sample is distinguished as the most durable sample with 33.16 % and
20.85 % of remaining weight, respectively.
As a result of the increasing reservations in environmental and health issues, development of new
biodegradable products attracts attention of researchers. However, biodegradable polymers
cannot be solely used and must be blended with other biodegradable additives to enhance their
mechanical properties and shape stability. Although the properties of PVA:starch blend films
containing different plasticizers have been investigated in literature, new plasticizers are still
needed for better thermoplastic processability of the blends in production scale. In this sense,
several polyol-based plasticizers have been investigated in different mass ratios for gelatinized
PVA:starch blend films.
5 wt% addition of the investigated plasticizers lowers the Tg point significantly, and different
plasticizing behaviors are observed with increasing plasticizer amount. The observed decrease
continue in a descending manner with 15 wt% 1,4-butanediol, 1,2,6-hexanetriol and
pentaerythritol addition. Xylitol leads to additional increase in segment mobility with 25 wt%
addition and mannitol stays almost the same despite its increasing amount in the blend. The
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difference of xylitol and mannitol is attributed to lower penetration capability of the molecules
into chain segments after the initial plasticization of 5 wt% addition.
The thermal decomposition data of polyol-based plasticizer containing samples indicate that
thermal resistivity is generally lower than neat PVA:starch blend film samples. However, the
orders of the plasticizers according to the 10 % weight loss temperature and residual weight
percentages at 300 oC generally indicate that the increasing hydroxyl number and molecular size
of the plasticizer enhance the thermal stability with a maximum in the presence of mannitol.
Based on the reported data, it can be consequently stated that although the number of hydrogen
groups on plasticizers are hydrogen bonding quarters for starch and PVA, molecular structure and
molecular geometry of plasticizers can prevent their penetration into chain segments and reduce
the intermolecular interactions, which in turn limit the expected plasticizing effect. Among the
investigated polyol-based plasticizers, 1,4-butanediol shows the highest plasticizing effect for
PVA:starch. It reduces the Tg point by approximately 27 oC, 31 oC and 39 oC, and 1,2,6-
hexanetriol reduces the Tg point by approximately 26 oC, 30 oC and 33 oC with 5 wt%, 15 wt%
and 25 wt% addition in the samples, respectively.
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PVA:starch blend films were prepared using a series of polyol-based plasticizers
5% (wt.) addition of the investigated plasticizers lowers the Tg point significantly
Different plasticization behaviors are observed with increasing plasticizer amount
Molecular geometry of plasticizers can prevent penetration into chain segments
1,4-butanediol shows the highest plasticizing effect for PVA:starch
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