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Effect of different polyol-based plasticizers on thermal properties of polyvinyl alcohol:starch blends
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.
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Effect of Different Polyol-Based Plasticizers on Thermal Properties of Polyvinyl Alcohol
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(PVA):Starch Blends Films
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Ahmet Alper Aydın1,* and Vladimir Ilberg2
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Istanbul Technical University, 34469 Maslak, Istanbul, Turkey. Email: [email protected]
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Triesdorf, Am Staudengarten 11, D-85350, Freising, Germany.
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Abstract
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A series of gelatinized polyvinyl alcohol (PVA):starch blends were prepared with various polyol-
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based plasticizers in 5 wt%, 15 wt% and 25 wt% ratios via solution casting method. The obtained
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films were analyzed by Fourier transform infrared (FT-IR) spectroscopy, differential scanning
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calorimetry (DSC) and thermogravimetric analysis (TGA). Remarkable changes have been
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observed in glass-transition temperature (Tg) and thermal stability of the samples containing
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varying concentrations of different plasticizers and they have been discussed in detail with
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respect to the conducted thermal and chemical analyses. The observed order of Tg point
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depression of the samples with containing 15 wt% plasticizer content is 1,4-butanediol - 1,2,6-
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hexanetriol - pentaerythriyol - xylitol - mannitol, which is similar to the sequence of the thermal
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stability changes of the samples. In the presence of 25 wt % 1,4-butanediol, the Tg point of
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PVA:starch films reduce from 76.1oC to 37.2oC.
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Keywords: starch; polyvinyl alcohol; plasticizer; polyol; thermal properties; glass transition
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Chemical compounds studied in this article: Corn Starch (PubChem CID: 24836924);
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Polyvinyl Alcohol (PubChem CID: 11119); 1,4-Butanediol (PubChem CID: 8064); 1,2,6-
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Hexanetriol (PubChem CID: 7823); Pentaerythritol (PubChem CID: 8285); Xylitol (PubChem
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CID: 6912); Mannitol (PubChem CID: 6251)
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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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1. Introduction
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Petroleum-based synthetic polymers with high molecular weight and hydrophobic character have
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been extensively used in different areas. However, their extensive use and ecological concerns
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have increased interest in biodegradable alternatives from renewable sources (Petersen et al.,
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1999; Weber et al., 2002).However, these polymers show very high chemical stability and
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degrade very slowly in the environment. In the 21st century, environmental and health issues
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associated with disposal and recycling of these products indicate major problems and extensive
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research activities continue for developing their biodegradable alternatives.
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There have been intensive attempts to develop biodegradable plastics with the purpose of
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protecting the environment. Biodegradable polymers offer environmentally friendly substitutes
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which can be degraded by microorganisms in soil or water. The approaches toward development
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of biodegradable polymers contain modification of non-degradable polymers by introducing
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degradable linkages or blending biodegradable polymers and tailoring their formulations so that
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the resulting materials have properties superior to the individual components (Tang, & Alavi,
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2011).
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Starch has been considered as one of the most suitable materials among natural biopolymers due
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to its low cost and abundant availability (Wang, Chang, &Zhang, 2010; Gross & Kalra, 2002).
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Polysaccharides such as starch, chitosan and cellulose are typical examples of natural
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biodegradable polymers with relatively good biocompatibility. However, starch-based products
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exhibit several disadvantages such as brittleness, strong hydrophilic character, poor mechanical
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properties and processability which limit their applications in material engineering. Therefore, the
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weakness of starch products must be compensated by blending starch with other synthesized
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degradable polymers (Shi et al., 2008). In this sense, blends with PVA are well suited to improve
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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
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(Nakayama, Takatsuka, & Matsuda, 1999; Cinelli, Chiellini, Gordon, & Chiellini, 2005). the
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making biodegradable blends with natural polymers due to its good physical properties, film-
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forming capability and water solubility
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Although PVA is a suitable solution to improve the properties of starch-based products, further
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improvement is still needed. As a result of the formed hydrogen bonds between PVA and starch
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molecules, the molecular movement and processability of the blend are restrained. At this point,
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plasticizers play an important role to reduce the strong interactions between PVA and starch
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molecules by forming new hydrogen bonds with PVA and starch. In this way, PVA:starch blends
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are processed into mouldable thermoplastic materials in the presence of suitable plasticizers
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(Chin & Te, 2008; Forssell et al., 1997; Raj, Siddaramaiah & Somashekar, 2004). Besides, the
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polarity of PVA increases the hydrolytic attack to the blend by atmospheric moisture and
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accelerates the break down in sugar molecules (Raj, Siddaramaiah, & Somashekar, 2004). Since
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starch and PVA molecules contain many hydroxyl groups, their blend films also have hydrophilic
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nature. Therefore, their thermal and mechanical properties and water resistance must be improved
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and tailored for different applications.
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Although PVA:starch blend films have been produced by means of solution casting, it is not an
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economic and efficient way compared to thermoplastic processing in larger production scale.
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Glass-transition temperature (Tg) plays an important role in production of thermoplastic products
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via extrusion. At the Tg point, the cohesive forces drastically decrease and the polymer expands.
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The increase in free volume reaches an extent that there is room for migration of segments, which
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provides flow of the polymer. Addition of plasticizers reduces molecular interactions, lowers the
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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
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point depression of the sample. The cohesive forces drastically decrease at the Tg point and the
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polymer expands to create room for migration of segments, which provides flow of the polymer.
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In the case of PVA and starch, strong molecular interactions are disturbed in the presence of
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plasticizers and the Tg point is reduced which makes the polymer more rubber-like (Jayasekara et
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al., 2003; Yoon, Chough, & Park, 2006a; Sreedhar et al., 2006).
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Different plasticizers like glycerol (Sreekumar, Al-Harthi, & De, 2012; Luo, Li, & Lin, 2012),
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polyethylene glycol (Sreedhar et al., 2005), sorbitol (Arvanitoyannis, Kolokuris, Nakayama,
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Yamamoto, & Aiba, 1997), sucrose (Arvanitoyannis, Kolokuris, Nakayama, Yamamoto, & Aiba,
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1997), urea (Luo, Li, & Lin, 2012), ascorbic acid (Yoon, 2014), citric acid (Shi et al., 2008;
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Yoon, Chough, & Park, 2006a), succinic acid (Yoon, Chough, & Park, 2006b), malic acid (Yoon,
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Chough, & Park, 2006b), tartaric acid (Yoon, Chough, & Park, 2006b) or more complex
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plasticizers (Zhou, Cu, Jia, & Xie, 2009) have been successfully employed to improve flexibility
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of the blends.
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Liu et al. (1999) compounded glycerol and water with PVA:starch blend in a single screw
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extruder. They reported that glycerol was much more effective than water as a plasticizer. In
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addition, Park et al. (2005) examined glycerol, sorbitol and citric acid as additives with different
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functional groups. They concluded that due to the increased hydrogen bonding in the presence of
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both hydroxyl group and carboxyl group, citric acid provided better film forming compared to
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sorbitol and glycerol. Similarly, Shi et al. (2008) reported another role of citric acid in the blend.
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According to their reported data, partial esterification takes place between starch (or PVA) and
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citric acid during processing at 140oC in the extruder. While partial esterification initially
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increases the tensile strength and Tg of the blend in the presence of 5% citric acid, further
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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
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modifying starch or PVA (Kim, & Lee, 2002; Kim, 2003), (ii) physically modifying by forming
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PVA/starch based nanocomposites (Dean, Do, Petinakis, Yu, 2008; Majdzadeh-Ardakani, &
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Nazari, 2010; Vasile et al., 2008; Tang, Alavi, & Herald, 2008), (iii) chemically modifying the
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PVA and starch during or after blending process with crosslinking agents such as boric acid (Yin,
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Li, Liu, & Li, 2005), borax (Sreedhar et al., 2005), epichlorohydrin (Sreedhar et al., 2006) and
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hexamethoxymethylmelamine (Chen et al., 1997).
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The aim of this paper is to introduce the influence of different polyol-based plasticizers on
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plasticization of neat PVA:starch blend with respect to the Tg point depression and thermal
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stability changes in the presence of plasticizers. For this purpose, 1,4-butanediol, 1,2,6-
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hexanetriol, pentaerythritol, xylitol and D-mannitol have been investigated as polyol-based new
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plasticizers and the changes in Tg point and thermal stability of the blends containing varying
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amounts of plasticizers have been discussed in detail with respect to the conducted thermal and
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chemical analyses.
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2. Materials and Methods
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2.1 Materials
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Corn starch was supplied by Sigma-Aldrich and it was composed of 73% amylopectin and 27%
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amylose. PVA was also obtained from Sigma-Aldrich, which was 99% hydrolyzed with an
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average molecular weight of 130.000 amu.
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The conducted strategy in choosing plasticizer was based on obtaining a series compounds with
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varying hydroxyl group functionality on the carbon chain. In this manner, the series of 1,4-
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butanediol (99%, Sigma), 1,2,6-hexanetriol (96%, Sigma), pentaerythritol (>99%, Sigma), xylitol
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(>99%, Sigma) and D-mannitol (>98%, Sigma), which contains polyols with different number of
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hydroxyl groups as shown in Fig. 1, was used as received from the supplier.
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Fig. 1. Chemical structures of the investigated plasticizers
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2.2 Preparation of PVA:Starch blend films
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PVA:starch (1:1, w/w) blend film samples were prepared by solution casting method according to
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the mass ratios given in Table 1. First, PVA was dissolved in 300 mL hot water at 97±2oC. After
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complete dissolution of PVA, calculated amount of plasticizer was added and stirred for 15
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minutes in order to maintain homogeneous distribution of plasticizer in hot water. Afterwards,
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dispersed starch in 100 mL water was added and the mixture was stirred for another 45 minutes.
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The mixtures were then casted onto petri dishes with similar weight (30 ± 2 g) and dried at 65oC
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to constant weight. In order to comparatively investigate the blends, Samples containing neat
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corn starch and PVA:starch were also prepared as reference.
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The peeled film samples were directly taken into sealed plastic bags and stored at room
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temperature in desiccator containing fresh silica-gel beads to maintain constant low-humidity.
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Samples exceeding 2 days were withdrawn and prepared again to guarantee low humidity of the
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samples.
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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)
5 15
1,2,6-Hexanetriol (wt% of the dry weight)
5 15 25 Xylitol
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Abbreviation
5 15 25 Mannitol
Abbreviation
(wt% of the dry weight)
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PSG-B5 PSG-B15 PSG-B25
1,4-Butanediol (wt% of the dry weight)
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Abbreviation
5 15 25
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2.3 Fourier transform infrared spectroscopy (FT-IR)
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FT-IR spectra of the synthesized high-chain fatty acid esters were recorded on a Perkin Elmer
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FT-IR Spectrum 100 spectrometer with universal ATR accessory between 4000 and 650 cm-1
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wavelength.
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2.4 Differential scanning calorimeter (DSC)
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A TA Instruments Q200 DSC was used for the calorimeter analyses of the samples. The
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measurements were carried out under inert nitrogen atmosphere at 50 ml/min flow rate. All the
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DSC thermal analyses were conducted at 5oC/min rate for the determination of glass transition
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points.
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DSC analyses were conducted according to the ASTM standard test methods with designation
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numbers E 793-06 and E 1269-11, explaining the determination of enthalpies of fusion and
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freezing and specific heat of liquids and solids, respectively. The temperature and heat
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calibrations of the instrument were systematically performed with sapphire and indium references
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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
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individual analyses in order to minimize the uncertainty.
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2.5 Thermo-gravimetric analyses (TGA)
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A NETZSCH STA 409 PC/PG was used for determination of thermo-gravimetric decomposition
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of the film samples, including decomposition behavior, onset temperature and weight losses at
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different temperatures of the samples. The analyses were carried out under inert argon
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atmosphere at 60 ml/min flow and 10oC/min heating rate between 30 and 600oC.
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The analyses were conducted according to the general principles given in BS EN ISO
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11358:1997. The weight and temperature calibrations of the instrument were made using the
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reference weight and according to the sensor calibration of the instrument, respectively. The
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calibration of the instrument was performed systematically prior to the first analysis of each
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workday.
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Every presented TGA data in this paper is calculated according to the results of at least 2
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individual analyses.
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3. Results and Discussion
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3.1 Plasticizers and hydrogen bonding (FT-IR)
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The hydrogen bonding plays an important role in formation of strong interactions between starch,
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PVA and plasticizer molecules and the FT-IR spectra enable the interactions to be identified. The
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changes in peak bandwidth, strength and frequency provide valuable data for interpretations on
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the formation of intermolecular hydrogen bonding in the samples.
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In general, the changes in band formations are clearly seen in the overlapped spectra of the blends
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given in Fig. 2(ii) compared to the polyol-based plasticizers in Fig. 2(i). In Fig. 2(ii)-a, the broad
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transmittance band of starch at 3293 cm-1 is assigned to the stretching vibration of –OH and the
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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
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858 cm-1 are assigned to the vibrations associated with the CH2 group. The peak at 1011 cm-1 is
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related to C–O bond stretching of C–O–C groups in anhydroglucose ring. The C–O bond
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stretching of C–O–H group is seen at 1150 cm-1. The given data are in good agreement with the
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literature (Fang et al., 2002; Pavlovic & Brandao, 2003; Ma & Yu, 2004).
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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
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The hydrogen bonding between –OH groups of starch, PVA and polyol-based plasticizers in the
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blends shifts the –OH stretching vibration bands of all neat polyol-based plasticizers to lower
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frequency region by around 4-14 cm-1 and the corresponding bands of blends get broader and
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stronger. Additionally, the positions of the C–O stretching bands of the C–O–H group located at
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around 1150 cm-1 significantly shift to lower frequencies as a result of the changed hydrogen
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bonding ratio in the blends. The single C–O stretching band of the C–O–C group in starch and
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PVA:starch samples transforms into double peak with the added plasticizers. The bound H2O
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shifts from 1638 cm-1 to higher frequencies by the addition of PVA and polyol-based plasticizers,
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indicating that the water molecules are more strongly hydrogen bonded in the presence of PVA
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and plasticizers (Wolkers et al., 2004). The details of the FT-IR spectra given in Fig. 2(ii) are
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tabulated in Table 2.
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Table 2 indicates that comparative changes are observed between spectra of polyol-based
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plasticizer containing samples and neat starch and PVA:starch samples, whereas spectra of
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plasticizer containing samples have generally close band frequencies as a result of their similar
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chemical structures. In PSG-X15 and PSG-M15 samples, C-H stretching is cleaved into two
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bands at around 2937-2932 and 2908-2910 cm-1. Besides, C-O stretching of C-O-C is located at
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higher frequencies compared to other polyol-based plasticizer containing samples.
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Table 2. Summary of FT-IR results PSGB15 (cm-1)
PSGH15 (cm-1)
PSGP15 (cm-1)
PSGX15 (cm-1)
PSGM15 (cm-1)
3293
3296
3292
3295
3304
3270
3287
2922
2931
2932
2933
2932
1638
1654
1654
1653
1653
1411, 858
1424, 844
1417, 845
1417, 847
1011
988
1014, 996
1150
1149
1147
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PVA:Starch (cm-1)
2932, 2910
1654
1654
1409, 848
1417, 842
1417, 843
1016, 996
1009, 991
1087, 1044
1077, 1024
1145
1146
1142
1143
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2937, 2908
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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
Starch (cm-1)
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Functional group
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3.2 The effects of plasticizers on thermal properties
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3.2.1 DSC analyses and changes in Tg points
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As it is given in Table 3 and Fig. 3-i, the casted sample of pure PVA has a clear Tg at 70.5oC.
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However, such a clear Tg cannot be observed for gelatinized starch, which could be because of its
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amorphous and hygroscopic nature. It has been stated in literature that the absence of its Tg may
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be due to amorphous chains surrounded by crystalline domains, presence of moisture, physical
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crosslinks inhibiting the movements of the amorphous chain segments or presence of
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intercrystalline phases (Sreedhar et al., 2005; Shi et al., 2008). Although there are no discernible
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changes in the DSC thermogram of gelatinized starch film, the PVA:starch (1:1, w/w) blend has a
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clear Tg at 76.1oC, which is higher than that of neat PVA as a result of the hydrogen bonding
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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
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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
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Abbreviation PVA PSG-B5 PSG-B15 PSG-B25 PSG-X5 PSG-X15 PSG-X25 PSG-P5 PSG-P15
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Plasticizers are low molecular weight substances, which reduce the Tg point of polymers and
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provide their flow by improving flexibility and processability. In this sense, the effects of
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plasticizers in different polymer blend compositions can be observed by investigating the degree
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of changes in Tg points at different concentrations (Jayasekara et al., 2003; Yoon, Chough, &
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Park, 2006a; Sreedhar et al., 2006).
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In the case of PVA:starch films, two types of hydrogen bonding interactions take place: (1)
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hydrogen bonding between hydroxyl groups of PVA and gelatinized starch and (2) hydrogen
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bonding between functional groups of PVA, starch and plasticizer. In the second type,
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plasticizers function as agents penetrating the matrix and interrupting the hydrogen bonding
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sequence between PVA and starch. They form hydrogen bonding bridges via functional groups in
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their chemical structure and spread throughout the matrix with their small molecular size and low
238
molecular weight. In this way, polar attractive forces are established between the plasticizer and
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chain segments, which are responsible for the reduction of Tg point and simultaneously,
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enhancement of chain segment mobility with better flexibility and processibility of the matrix
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(Chin & Te, 2008; Forssell et al., 1997; Raj, Siddaramaiah, & Somashekar, 2004).
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The hydroxyl groups are hydrogen bonding quarters on the investigated plasticizers (Fig. 1)
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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
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significantly drops the Tg point in Table 3. The Tg points shift significantly to lower temperature
246
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
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Unlike xylitol and mannitol, the Tg points continue decreasing in the presence of 15 wt% and 25
252
wt% 1,4-butanediol, 1,2,6-hexanetriol and pentaerythritol as a result of increasing number of
253
available hydroxyl groups. However, Tg points do not significantly decrease in the samples
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containing 15 wt% xylitol and mannitol. Only for xylitol, increase in its mass ratio to 25 wt%
255
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
257
molecular structures. Compared to 1,4-butanediol, 1,2,6-hexanetriol and pentaerythritol, they are
258
relatively larger molecules with 5 and 6 hydroxyl groups, respectively. Probably, further
259
penetration into chain segments of PVA and starch is prevented due to their larger molecular
260
geometry after the initial plasticization of 5 wt% addition. Consequently, it can be mentioned that
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mannitol molecules tend to interact with each other and do not significantly improve the thermal
262
properties of the blend, whereas smaller xylitol molecules can further play role in plasticization
263
when they are found in high amount.
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3.2.2 Thermal-decomposition behaviors and thermogravimetric analyses
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In the given figures, three distinct regions of mass loss can be seen. There are generally three
266
distinct mass loss regions in PVA:starch samples reported in literature. The first region (between
267
75oC and 200oC) is attributed to the loss of loosely bound water, accompanied by the formation
268
of volatile disintegrated products such as dislocation of the plasticizers in the blend. The second
269
region is described as the main decomposition step and the final stage is the carbonization of the
270
organic matter (above 500oC) (Galdeno et al., 2009; Luo, X., Li, J., & Lin, X, 2012; Saiah et al.,
271
2009; Shi et al., 2011). The thermal decomposition behaviors of various PVA:starch films
272
with/without polyol-based plasticizers are given in Fig. 4.
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In addition to the overlapped thermal decomposition curves in Fig. 4, the thermal decomposition
274
data are also tabulated in Table 4 to present the 10 % weight loss temperature and residual
275
weights at 300oC, 400oC and 500oC for reference samples (starch, PVA, PVA:starch) and 15 wt%
276
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
at 500oC
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
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at 300 C
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Starch PVA PVA:Starch PSG-B15 PSG-H15 PSG-P15 PSG-X15 PSG-M15
o
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Abbreviation
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
285
resistive cyclic hemiacetal in starch structure and development of blending towards high-energy
286
stability of the mixture (Sin et al., 2011). Therefore, PVA:starch sample has closer 10 %
287
decomposition temperature to gelatinized neat starch instead of PVA and less weight loss than
288
neat PVA at 300oC, 400oC and 500oC compared to PVA.
289
When the thermal decomposition data of polyol-based plasticizer containing samples are
290
examined, reductions in thermal resistivity are generally observed, except for mannitol containing
291
sample, compared to the PVA:starch sample. Although the mass loss order of different
292
plasticizers is attributed to their volatility difference in literature (Ma, Yu, & Wan, 2006), the
293
mass loss order of samples containing different plasticizers is also related to intermolecular
294
interactions and mobility between the plasticizer, PVA and starch chains according to the
295
interpreted data below.
296
As PVA:starch sample has closer thermal stability to starch due to the development of blending
297
towards high-energy stability, it is expected that higher the plasticization effect, lower the thermal
298
stability of the blend sample.
299
Other than the exception of 1,4-butanediol and 1,2,6-hexanetriol containing samples, the
300
increasing hydroxyl number and molecular size of the plasticizer enhance the thermal stability
301
with a maximum in the presence of mannitol. Although the increase in molecular size of the
302
plasticizers decreases their penetration ability into PVA and starch chain segments and limit the
303
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
305
high-energy stability. The exceptional behavior of 1,4-butanediol and 1,2,6-hexanetriol
306
containing samples might be attributed to their volatility difference. Therefore, the thermal
307
stability of PVA:starch:plasticizer samples is related to not only the volatility difference of the
308
plasticizers, but also to the mobility between the plasticizer, PVA and starch chains.
309
The mannitol containing sample shows better thermal endurance than neat starch and PVA:starch
310
samples at 300 oC and its 10 % weight loss temperature is at 298.7 oC, which is the highest
311
among the analyzed samples. However, its decomposition rate later gets higher and at 400oC and
312
500oC, the neat PVA:starch sample is distinguished as the most durable sample with 33.16 % and
313
20.85 % of remaining weight, respectively.
314
4. Conclusion
315
As a result of the increasing reservations in environmental and health issues, development of new
316
biodegradable products attracts attention of researchers. However, biodegradable polymers
317
cannot be solely used and must be blended with other biodegradable additives to enhance their
318
mechanical properties and shape stability. Although the properties of PVA:starch blend films
319
containing different plasticizers have been investigated in literature, new plasticizers are still
320
needed for better thermoplastic processability of the blends in production scale. In this sense,
321
several polyol-based plasticizers have been investigated in different mass ratios for gelatinized
322
PVA:starch blend films.
323
5 wt% addition of the investigated plasticizers lowers the Tg point significantly, and different
324
plasticizing behaviors are observed with increasing plasticizer amount. The observed decrease
325
continue in a descending manner with 15 wt% 1,4-butanediol, 1,2,6-hexanetriol and
326
pentaerythritol addition. Xylitol leads to additional increase in segment mobility with 25 wt%
327
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
329
into chain segments after the initial plasticization of 5 wt% addition.
330
The thermal decomposition data of polyol-based plasticizer containing samples indicate that
331
thermal resistivity is generally lower than neat PVA:starch blend film samples. However, the
332
orders of the plasticizers according to the 10 % weight loss temperature and residual weight
333
percentages at 300 oC generally indicate that the increasing hydroxyl number and molecular size
334
of the plasticizer enhance the thermal stability with a maximum in the presence of mannitol.
335
Based on the reported data, it can be consequently stated that although the number of hydrogen
336
groups on plasticizers are hydrogen bonding quarters for starch and PVA, molecular structure and
337
molecular geometry of plasticizers can prevent their penetration into chain segments and reduce
338
the intermolecular interactions, which in turn limit the expected plasticizing effect. Among the
339
investigated polyol-based plasticizers, 1,4-butanediol shows the highest plasticizing effect for
340
PVA:starch. It reduces the Tg point by approximately 27 oC, 31 oC and 39 oC, and 1,2,6-
341
hexanetriol reduces the Tg point by approximately 26 oC, 30 oC and 33 oC with 5 wt%, 15 wt%
342
and 25 wt% addition in the samples, respectively.
343
References
344
Arvanitoyannis, I., Kolokuris, I., Nakayama, A., Yamamoto, N., & Aiba, S. (1997). Physico-
345
chemical studies of chitosan-poly (vinyl alcohol) blends plasticized with sorbitol and sucrose.
346
Carbohydrate Polymers, 34, 9-19.
347
Chen, L., Iman, S. H., Stein, T. M., Gordon, S. H., Hou, C. T., & Greene, R. V. (1997). Starch-
348
polyvinyl alcohol cast film-performance and biodegredation. Polymer Preprints, 37, 461-462.
349
Chin, A. L., & Te, H. K. (2008). Shear and elongational flow properties of thermoplastic
350
polyvinyl alcohol melts with different plasticizer contents and degrees of polymerization. Journal
351
of Materials Processing Technology, 200, 331-338.
Ac ce p
te
d
M
an
us
cr
ip t
328
18 Page 18 of 24
Cinelli, P., Chiellini, E., Gordon, L. S. H., & Chiellini, L. E. (2005). Characterization of
353
biodegredable composite films prepared from blends of poly(vinyl alcohol), cornstarch, and
354
lignocellulosic fibre. Journal of Polymer Environment, 13, 47-59.
355
Dean, K. M., DO, M. D., Petinakis, E., & Yu, L. (2008). Key interactions in biodegradable
356
thermoplastic
357
Composites Science and Technology, 68(6), 1453-1462.
358
Fang, J. M., Fowler, P. A., Tomkinson, J., & Hill, C. A. S. (2002). The preparation and
359
characterization of a series of chemically modified potato starch. Carbohydrate Polymers, 47,
360
245-252.
361
Forssell, P. M., Mikkila, J. M., Moates, G. K., & Parker, R. (1997). Phase and glass transition
362
behaviour of concentrated barley starch-glycerol-water mixtures, a model for thermoplastic
363
starch. Carbohydrate Polymers, 34, 275-282.
364
Galdeano, M. C., Grossmann, M. V. E., Mali, S., Bello-Perez, L. A., Garcia, M. A., & Zamudio-
365
Flores, P. B. (2009). Effects of production process and plasticizers on stability of films and sheets
366
of oat starch. Materials Science and Engineering: C, 29, 492–498.
367
Gross, R.A., & Kalra, B. (2002). Biodegradable polymers for the environment. Science, 297, 803-
368
807.
369
Jayasekara, R., Harding, I., Bowater, I., Christie, G. B. Y., Lonergan, G. T. J. (2003).
370
Biodegradation by composting of surface modified starch and PVA blended films. Journal of
371
Polymers and the Environment, 11, 49-56.
372
Kim, M. (2003). Evaluation of degradability of hydroxypropylated potato starch/polyethylene
373
blend films. Carbohydrate Polymers, 54, 173-181.
374
Kim, M., & Lee, S-J. (2002). Characteristics of crosslinked potato starch and starch-filled linear
375
low-density polyethylene films. Carbohydrate Polymers, 50, 331-337.
micro-
and
nanocomposites.
cr
alcohol)/montmorillonite
Ac ce p
te
d
M
an
us
starch/poly(vinyl
ip t
352
19 Page 19 of 24
Liu, Z. Q., Feng, Y., & Yi, X. S. (1999). Thermoplastic starch/PVAI compounds: Preparation,
377
processing and properties. Journal of Applied Polymer Science, 74, 2667-2673.
378
Luo, X., Li, J., & Lin, X. (2012). Effect of gelatinization and additives on morphology and
379
thermal behavior of corn starch/PVA blend films. Carbohydrate Polymers, 90, 1595-1600.
380
Ma, X. F., Yu, J. G., & Wan, J. J. (2006). Urea and ethanolamine as a mixed plasticizer for
381
thermoplastic starch. Carbohydrate Polymers, 64, 267-273.
382
Ma, X., Yu, J. (2004). The effects of plasticizers containing amide groups on the properties of
383
thermoplastic starch. Starch/Stärke, 56, 545–551.
384
Majdzadeh-Ardakani, K., & Nazari, B. (2010). Improving the mechanical properties of
385
thermoplastic starch/poly (vinyl alcohol)/clay nanocomposites. Composites Science and
386
Technology, 70, 1557-1563.
387
Nakayama, Y., Takatsuka, M., & Matsuda, T. (1999). Surface hydrogelation using photolysis of
388
dithiocarbamate or xanthate: Hydrogelation, surface fixation, and bioactive substance
389
immobilization. Langmuir, 15, 1667-1672.
390
Park, H., Chough, S., Yun, Y., & Yoon, S. (2005). Properties of starch/PVA blend films
391
containing citric acid as additive. Journal of Polymers and the Environment, 13(4), 375-382.
392
Pavlovic, S., & Brandao, P. R. G. (2003). Adsorption of starch, amylose, amylopectin and
393
glucose monomer and their effect on the flotation of hematite and quartz. Minerals Engineering,
394
16, 1117-1122.
395
Petersen, K., Nielsen, P.V., Bertelsen, G., Lawther, M., Olsen, M., Nilsson, N.H., & Mortensen,
396
G. (1999). Potential of biobased materials for food packaging. Trends in Food Science &
397
Technology, 10, 52-68.
398
Raj, B., Sidddaramaiah, S., & Somashekar, R. (2004). Structure-property relation in polyvinyl
399
alcohol/starch composites. Journal of Applied Polymer Science, 91, 630-635.
Ac ce p
te
d
M
an
us
cr
ip t
376
20 Page 20 of 24
Saiah, R., Sreekumar, P. A., Leblanc, N., & Saiter, J.-M. (2009). Structure and thermal stability
401
ofthermoplasticfilms basedon wheatflourmodifiedbymonoglyceride. Industrial Crops and
402
Products, 29, 241–247.
403
Shi, Q. F., Chen, C., Gao, L., Jiao, L., Xu, H. Y., & Guo, W. H. (2011). Physical and degradation
404
properties of binary or ternary blends composed of poly (lactic acid), thermoplastic starch and
405
GMA grafted POE. Polymer Degradation and Stability, 96, 175–182.
406
Shi, R., Bi, J., Zhang, Z., Zhu, A., Chen, D., Zhou, X., Zhang, L., & Tian, W. (2008). The effect
407
of citric acid on the structural properties and cytotoxicity of the polyvinyl alcohol/starch films
408
when molding at high temperature. Carbohydrate Polymers, 74, 763-770.
409
Sin, L. T., Rahman, W. A. W. A., Rahmat, A. R., & Mokhtar, M. (2011). Determination of
410
thermal stability and activation energy of polyvinyl alcohol–cassava starch blends. Carbohydrate
411
Polymers, 83, 303-305.
412
Sreedhar, B., Chattopadhyay, D. K., Karunakar, M. S. H., & Sastry, A. R. K. (2006). Thermal
413
and surface characterization of plasticized starch polyvinyl alcohol blends crosslinked with
414
epichlorohydrin. Journal of Applied Polymer Science, 101, 25-34.
415
Sreedhar, B., Sairam, M., Chattopadhyay, D. K., Syamala Rathnam, P. A., & Mohan Rao, D. V.
416
(2005). Thermal, mechanical and surface characterization of starch-poly(vinyl alcohol) blends
417
and borax-crosslinked films. Journal of Applied Polymer Science, 96, 1313-1322.
Ac ce p
te
d
M
an
us
cr
ip t
400
21 Page 21 of 24
Sreekumar, P. A., Al-Harthi, M. A., & De, S. K. (2012). Effect of glycerol on thermal and
419
mechanical properties of polyvinyl alcohol/starch blends. Journal of Applied Polymer Science,
420
123, 135-142.
421
Tang, X. Z., Alavi, S., & Herald, T. (2008). Effects of plasticizers on the structure and properties
422
of starch-clay nanocomposite films. Carbohydrate Polymers, 74, 552-558.
423
Tang, X., & Alavi, S. (2011). Recent advances in starch, polyvinyl alcohol based polymer blends,
424
nanocomposites and their biodegradability. Carbohydrate Polymers, 85, 7-16.
425
Vasile, C., Stoleriu, A., Popescu, M. C., Duncianu, C., Kelnar, I., & Dimonie, D. (2008).
426
Morphology and thermal properties of some green starch/poly (vinyl alcohol)/montmorillonite
427
nanocomposites. Cellulose Chemistry and Technology, 42(9-10), 549-568.
428
Wang, Y., Chang, C., & Zhang, L. (2010). Effects of Freezing/Thawing Cycles and Cellulose
429
Nanowhiskers
430
Macromolecular Materials and Engineering, 295, 137-145.
431
Weber, C.J., Haugaard, V., Festersen, R., & Bertelsen, G. (2002) Production and application of
432
biobased packaging materials for the food industry. Food Additives & Contaminants, 19, 172-
433
177.
434
Wolkers, W. F., Oliver, A. E., Tablin, F., & Crowe, J. H. (2004). A Fourier-transform infrared
435
spectroscopy study of sugar glasses. Carbohydrate Research, 339 (6), 1077-1085.
436
Yin, Y., Li, J., Liu, Y., & Li, Z. (2005). Starch crosslinked with poly(vinyl alcohol) by boric acid.
437
Journal of Applied Polymer Science, 96, 1394-1397.
438
Yoon, S. D., Chough, S. H., & Park, H. R. (2006a). Properties of starch-based blend films using
439
citric acid as additive. Journal of Applied Polymer Science, 100, 2554-2560.
Structure
and
Properties
of
Biocompatible
Starch/PVA
Sponges.
Ac ce p
te
d
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M
an
us
cr
ip t
418
22 Page 22 of 24
Yoon, S. D., Chough, S. H., & Park, H. R. (2006b). Effects of additives with different functional
441
groups on the physical properties of starch/PVA blend film. Journal of Applied Polymer Science,
442
100, 3733-3740.
443
Yoon, S. D. (2014). Cross-Linked Potato Starch-Based Blend Films Using Ascorbic Acid as a
444
Plasticizer. Journal of Agricultural and Food Chemistry, 62, 1755-1764.
445
Zhou, X. Y., Cu, Y. F., Jia, D. M., & Xie, D. (2009). Effect of a complex plasticizer on the
446
structure and properties of the thermoplastic PVA/starch blends. Polymer Plastics Technology
447
and Engineering, 48(5), 489-495.
us
cr
ip t
440
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Highlights -
PVA:starch blend films were prepared using a series of polyol-based plasticizers
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-
5% (wt.) addition of the investigated plasticizers lowers the Tg point significantly
451
-
Different plasticization behaviors are observed with increasing plasticizer amount
452
-
Molecular geometry of plasticizers can prevent penetration into chain segments
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1,4-butanediol shows the highest plasticizing effect for PVA:starch
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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.
1
Effect of Different Polyol-Based Plasticizers on Thermal Properties of Polyvinyl Alcohol
2
(PVA):Starch Blends Films
3
Ahmet Alper Aydın1,* and Vladimir Ilberg2
4
1
5
Istanbul Technical University, 34469 Maslak, Istanbul, Turkey. Email: [email protected]
6
2
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Triesdorf, Am Staudengarten 11, D-85350, Freising, Germany.
8
Abstract
9
A series of gelatinized polyvinyl alcohol (PVA):starch blends were prepared with various polyol-
10
based plasticizers in 5 wt%, 15 wt% and 25 wt% ratios via solution casting method. The obtained
11
films were analyzed by Fourier transform infrared (FT-IR) spectroscopy, differential scanning
12
calorimetry (DSC) and thermogravimetric analysis (TGA). Remarkable changes have been
13
observed in glass-transition temperature (Tg) and thermal stability of the samples containing
14
varying concentrations of different plasticizers and they have been discussed in detail with
15
respect to the conducted thermal and chemical analyses. The observed order of Tg point
16
depression of the samples with containing 15 wt% plasticizer content is 1,4-butanediol - 1,2,6-
17
hexanetriol - pentaerythriyol - xylitol - mannitol, which is similar to the sequence of the thermal
18
stability changes of the samples. In the presence of 25 wt % 1,4-butanediol, the Tg point of
19
PVA:starch films reduce from 76.1oC to 37.2oC.
20
Keywords: starch; polyvinyl alcohol; plasticizer; polyol; thermal properties; glass transition
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Chemical compounds studied in this article: Corn Starch (PubChem CID: 24836924);
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Polyvinyl Alcohol (PubChem CID: 11119); 1,4-Butanediol (PubChem CID: 8064); 1,2,6-
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Hexanetriol (PubChem CID: 7823); Pentaerythritol (PubChem CID: 8285); Xylitol (PubChem
24
CID: 6912); Mannitol (PubChem CID: 6251)
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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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1. Introduction
26
Petroleum-based synthetic polymers with high molecular weight and hydrophobic character have
27
been extensively used in different areas. However, their extensive use and ecological concerns
28
have increased interest in biodegradable alternatives from renewable sources (Petersen et al.,
29
1999; Weber et al., 2002).However, these polymers show very high chemical stability and
30
degrade very slowly in the environment. In the 21st century, environmental and health issues
31
associated with disposal and recycling of these products indicate major problems and extensive
32
research activities continue for developing their biodegradable alternatives.
33
There have been intensive attempts to develop biodegradable plastics with the purpose of
34
protecting the environment. Biodegradable polymers offer environmentally friendly substitutes
35
which can be degraded by microorganisms in soil or water. The approaches toward development
36
of biodegradable polymers contain modification of non-degradable polymers by introducing
37
degradable linkages or blending biodegradable polymers and tailoring their formulations so that
38
the resulting materials have properties superior to the individual components (Tang, & Alavi,
39
2011).
40
Starch has been considered as one of the most suitable materials among natural biopolymers due
41
to its low cost and abundant availability (Wang, Chang, &Zhang, 2010; Gross & Kalra, 2002).
42
Polysaccharides such as starch, chitosan and cellulose are typical examples of natural
43
biodegradable polymers with relatively good biocompatibility. However, starch-based products
44
exhibit several disadvantages such as brittleness, strong hydrophilic character, poor mechanical
45
properties and processability which limit their applications in material engineering. Therefore, the
46
weakness of starch products must be compensated by blending starch with other synthesized
47
degradable polymers (Shi et al., 2008). In this sense, blends with PVA are well suited to improve
48
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
50
(Nakayama, Takatsuka, & Matsuda, 1999; Cinelli, Chiellini, Gordon, & Chiellini, 2005). the
51
making biodegradable blends with natural polymers due to its good physical properties, film-
52
forming capability and water solubility
53
Although PVA is a suitable solution to improve the properties of starch-based products, further
54
improvement is still needed. As a result of the formed hydrogen bonds between PVA and starch
55
molecules, the molecular movement and processability of the blend are restrained. At this point,
56
plasticizers play an important role to reduce the strong interactions between PVA and starch
57
molecules by forming new hydrogen bonds with PVA and starch. In this way, PVA:starch blends
58
are processed into mouldable thermoplastic materials in the presence of suitable plasticizers
59
(Chin & Te, 2008; Forssell et al., 1997; Raj, Siddaramaiah & Somashekar, 2004). Besides, the
60
polarity of PVA increases the hydrolytic attack to the blend by atmospheric moisture and
61
accelerates the break down in sugar molecules (Raj, Siddaramaiah, & Somashekar, 2004). Since
62
starch and PVA molecules contain many hydroxyl groups, their blend films also have hydrophilic
63
nature. Therefore, their thermal and mechanical properties and water resistance must be improved
64
and tailored for different applications.
65
Although PVA:starch blend films have been produced by means of solution casting, it is not an
66
economic and efficient way compared to thermoplastic processing in larger production scale.
67
Glass-transition temperature (Tg) plays an important role in production of thermoplastic products
68
via extrusion. At the Tg point, the cohesive forces drastically decrease and the polymer expands.
69
The increase in free volume reaches an extent that there is room for migration of segments, which
70
provides flow of the polymer. Addition of plasticizers reduces molecular interactions, lowers the
71
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
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point depression of the sample. The cohesive forces drastically decrease at the Tg point and the
74
polymer expands to create room for migration of segments, which provides flow of the polymer.
75
In the case of PVA and starch, strong molecular interactions are disturbed in the presence of
76
plasticizers and the Tg point is reduced which makes the polymer more rubber-like (Jayasekara et
77
al., 2003; Yoon, Chough, & Park, 2006a; Sreedhar et al., 2006).
78
Different plasticizers like glycerol (Sreekumar, Al-Harthi, & De, 2012; Luo, Li, & Lin, 2012),
79
polyethylene glycol (Sreedhar et al., 2005), sorbitol (Arvanitoyannis, Kolokuris, Nakayama,
80
Yamamoto, & Aiba, 1997), sucrose (Arvanitoyannis, Kolokuris, Nakayama, Yamamoto, & Aiba,
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1997), urea (Luo, Li, & Lin, 2012), ascorbic acid (Yoon, 2014), citric acid (Shi et al., 2008;
82
Yoon, Chough, & Park, 2006a), succinic acid (Yoon, Chough, & Park, 2006b), malic acid (Yoon,
83
Chough, & Park, 2006b), tartaric acid (Yoon, Chough, & Park, 2006b) or more complex
84
plasticizers (Zhou, Cu, Jia, & Xie, 2009) have been successfully employed to improve flexibility
85
of the blends.
86
Liu et al. (1999) compounded glycerol and water with PVA:starch blend in a single screw
87
extruder. They reported that glycerol was much more effective than water as a plasticizer. In
88
addition, Park et al. (2005) examined glycerol, sorbitol and citric acid as additives with different
89
functional groups. They concluded that due to the increased hydrogen bonding in the presence of
90
both hydroxyl group and carboxyl group, citric acid provided better film forming compared to
91
sorbitol and glycerol. Similarly, Shi et al. (2008) reported another role of citric acid in the blend.
92
According to their reported data, partial esterification takes place between starch (or PVA) and
93
citric acid during processing at 140oC in the extruder. While partial esterification initially
94
increases the tensile strength and Tg of the blend in the presence of 5% citric acid, further
95
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
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modifying starch or PVA (Kim, & Lee, 2002; Kim, 2003), (ii) physically modifying by forming
98
PVA/starch based nanocomposites (Dean, Do, Petinakis, Yu, 2008; Majdzadeh-Ardakani, &
99
Nazari, 2010; Vasile et al., 2008; Tang, Alavi, & Herald, 2008), (iii) chemically modifying the
100
PVA and starch during or after blending process with crosslinking agents such as boric acid (Yin,
101
Li, Liu, & Li, 2005), borax (Sreedhar et al., 2005), epichlorohydrin (Sreedhar et al., 2006) and
102
hexamethoxymethylmelamine (Chen et al., 1997).
103
The aim of this paper is to introduce the influence of different polyol-based plasticizers on
104
plasticization of neat PVA:starch blend with respect to the Tg point depression and thermal
105
stability changes in the presence of plasticizers. For this purpose, 1,4-butanediol, 1,2,6-
106
hexanetriol, pentaerythritol, xylitol and D-mannitol have been investigated as polyol-based new
107
plasticizers and the changes in Tg point and thermal stability of the blends containing varying
108
amounts of plasticizers have been discussed in detail with respect to the conducted thermal and
109
chemical analyses.
110
2. Materials and Methods
111
2.1 Materials
112
Corn starch was supplied by Sigma-Aldrich and it was composed of 73% amylopectin and 27%
113
amylose. PVA was also obtained from Sigma-Aldrich, which was 99% hydrolyzed with an
114
average molecular weight of 130.000 amu.
115
The conducted strategy in choosing plasticizer was based on obtaining a series compounds with
116
varying hydroxyl group functionality on the carbon chain. In this manner, the series of 1,4-
117
butanediol (99%, Sigma), 1,2,6-hexanetriol (96%, Sigma), pentaerythritol (>99%, Sigma), xylitol
118
(>99%, Sigma) and D-mannitol (>98%, Sigma), which contains polyols with different number of
119
hydroxyl groups as shown in Fig. 1, was used as received from the supplier.
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Fig. 1. Chemical structures of the investigated plasticizers
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2.2 Preparation of PVA:Starch blend films
123
PVA:starch (1:1, w/w) blend film samples were prepared by solution casting method according to
124
the mass ratios given in Table 1. First, PVA was dissolved in 300 mL hot water at 97±2oC. After
125
complete dissolution of PVA, calculated amount of plasticizer was added and stirred for 15
126
minutes in order to maintain homogeneous distribution of plasticizer in hot water. Afterwards,
127
dispersed starch in 100 mL water was added and the mixture was stirred for another 45 minutes.
128
The mixtures were then casted onto petri dishes with similar weight (30 ± 2 g) and dried at 65oC
129
to constant weight. In order to comparatively investigate the blends, Samples containing neat
130
corn starch and PVA:starch were also prepared as reference.
131
The peeled film samples were directly taken into sealed plastic bags and stored at room
132
temperature in desiccator containing fresh silica-gel beads to maintain constant low-humidity.
133
Samples exceeding 2 days were withdrawn and prepared again to guarantee low humidity of the
134
samples.
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138
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)
5 15
1,2,6-Hexanetriol (wt% of the dry weight)
5 15 25 Xylitol
ip t
Abbreviation
5 15 25 Mannitol
Abbreviation
(wt% of the dry weight)
cr
PSG-B5 PSG-B15 PSG-B25
1,4-Butanediol (wt% of the dry weight)
us
Abbreviation
5 15 25
an
139
2.3 Fourier transform infrared spectroscopy (FT-IR)
141
FT-IR spectra of the synthesized high-chain fatty acid esters were recorded on a Perkin Elmer
142
FT-IR Spectrum 100 spectrometer with universal ATR accessory between 4000 and 650 cm-1
143
wavelength.
144
2.4 Differential scanning calorimeter (DSC)
145
A TA Instruments Q200 DSC was used for the calorimeter analyses of the samples. The
146
measurements were carried out under inert nitrogen atmosphere at 50 ml/min flow rate. All the
147
DSC thermal analyses were conducted at 5oC/min rate for the determination of glass transition
148
points.
149
DSC analyses were conducted according to the ASTM standard test methods with designation
150
numbers E 793-06 and E 1269-11, explaining the determination of enthalpies of fusion and
151
freezing and specific heat of liquids and solids, respectively. The temperature and heat
152
calibrations of the instrument were systematically performed with sapphire and indium references
153
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
155
individual analyses in order to minimize the uncertainty.
156
2.5 Thermo-gravimetric analyses (TGA)
157
A NETZSCH STA 409 PC/PG was used for determination of thermo-gravimetric decomposition
158
of the film samples, including decomposition behavior, onset temperature and weight losses at
159
different temperatures of the samples. The analyses were carried out under inert argon
160
atmosphere at 60 ml/min flow and 10oC/min heating rate between 30 and 600oC.
161
The analyses were conducted according to the general principles given in BS EN ISO
162
11358:1997. The weight and temperature calibrations of the instrument were made using the
163
reference weight and according to the sensor calibration of the instrument, respectively. The
164
calibration of the instrument was performed systematically prior to the first analysis of each
165
workday.
166
Every presented TGA data in this paper is calculated according to the results of at least 2
167
individual analyses.
168
3. Results and Discussion
169
3.1 Plasticizers and hydrogen bonding (FT-IR)
170
The hydrogen bonding plays an important role in formation of strong interactions between starch,
171
PVA and plasticizer molecules and the FT-IR spectra enable the interactions to be identified. The
172
changes in peak bandwidth, strength and frequency provide valuable data for interpretations on
173
the formation of intermolecular hydrogen bonding in the samples.
174
In general, the changes in band formations are clearly seen in the overlapped spectra of the blends
175
given in Fig. 2(ii) compared to the polyol-based plasticizers in Fig. 2(i). In Fig. 2(ii)-a, the broad
176
transmittance band of starch at 3293 cm-1 is assigned to the stretching vibration of –OH and the
177
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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8 Page 8 of 24
the bound water in starch with the formed hydrogen bonds. The bands located at 1411 cm-1 and
179
858 cm-1 are assigned to the vibrations associated with the CH2 group. The peak at 1011 cm-1 is
180
related to C–O bond stretching of C–O–C groups in anhydroglucose ring. The C–O bond
181
stretching of C–O–H group is seen at 1150 cm-1. The given data are in good agreement with the
182
literature (Fang et al., 2002; Pavlovic & Brandao, 2003; Ma & Yu, 2004).
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178
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
189
blends shifts the –OH stretching vibration bands of all neat polyol-based plasticizers to lower
190
frequency region by around 4-14 cm-1 and the corresponding bands of blends get broader and
191
stronger. Additionally, the positions of the C–O stretching bands of the C–O–H group located at
192
around 1150 cm-1 significantly shift to lower frequencies as a result of the changed hydrogen
193
bonding ratio in the blends. The single C–O stretching band of the C–O–C group in starch and
194
PVA:starch samples transforms into double peak with the added plasticizers. The bound H2O
195
shifts from 1638 cm-1 to higher frequencies by the addition of PVA and polyol-based plasticizers,
196
indicating that the water molecules are more strongly hydrogen bonded in the presence of PVA
197
and plasticizers (Wolkers et al., 2004). The details of the FT-IR spectra given in Fig. 2(ii) are
198
tabulated in Table 2.
199
Table 2 indicates that comparative changes are observed between spectra of polyol-based
200
plasticizer containing samples and neat starch and PVA:starch samples, whereas spectra of
201
plasticizer containing samples have generally close band frequencies as a result of their similar
202
chemical structures. In PSG-X15 and PSG-M15 samples, C-H stretching is cleaved into two
203
bands at around 2937-2932 and 2908-2910 cm-1. Besides, C-O stretching of C-O-C is located at
204
higher frequencies compared to other polyol-based plasticizer containing samples.
206
cr
us
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Table 2. Summary of FT-IR results PSGB15 (cm-1)
PSGH15 (cm-1)
PSGP15 (cm-1)
PSGX15 (cm-1)
PSGM15 (cm-1)
3293
3296
3292
3295
3304
3270
3287
2922
2931
2932
2933
2932
1638
1654
1654
1653
1653
1411, 858
1424, 844
1417, 845
1417, 847
1011
988
1014, 996
1150
1149
1147
ip t
PVA:Starch (cm-1)
2932, 2910
1654
1654
1409, 848
1417, 842
1417, 843
1016, 996
1009, 991
1087, 1044
1077, 1024
1145
1146
1142
1143
cr
2937, 2908
us
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
Starch (cm-1)
an
Functional group
M
212
3.2 The effects of plasticizers on thermal properties
214
3.2.1 DSC analyses and changes in Tg points
215
As it is given in Table 3 and Fig. 3-i, the casted sample of pure PVA has a clear Tg at 70.5oC.
216
However, such a clear Tg cannot be observed for gelatinized starch, which could be because of its
217
amorphous and hygroscopic nature. It has been stated in literature that the absence of its Tg may
218
be due to amorphous chains surrounded by crystalline domains, presence of moisture, physical
219
crosslinks inhibiting the movements of the amorphous chain segments or presence of
220
intercrystalline phases (Sreedhar et al., 2005; Shi et al., 2008). Although there are no discernible
221
changes in the DSC thermogram of gelatinized starch film, the PVA:starch (1:1, w/w) blend has a
222
clear Tg at 76.1oC, which is higher than that of neat PVA as a result of the hydrogen bonding
223
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
ip t
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
us
Abbreviation PVA PSG-B5 PSG-B15 PSG-B25 PSG-X5 PSG-X15 PSG-X25 PSG-P5 PSG-P15
cr
226
Plasticizers are low molecular weight substances, which reduce the Tg point of polymers and
228
provide their flow by improving flexibility and processability. In this sense, the effects of
229
plasticizers in different polymer blend compositions can be observed by investigating the degree
230
of changes in Tg points at different concentrations (Jayasekara et al., 2003; Yoon, Chough, &
231
Park, 2006a; Sreedhar et al., 2006).
232
In the case of PVA:starch films, two types of hydrogen bonding interactions take place: (1)
233
hydrogen bonding between hydroxyl groups of PVA and gelatinized starch and (2) hydrogen
234
bonding between functional groups of PVA, starch and plasticizer. In the second type,
235
plasticizers function as agents penetrating the matrix and interrupting the hydrogen bonding
236
sequence between PVA and starch. They form hydrogen bonding bridges via functional groups in
237
their chemical structure and spread throughout the matrix with their small molecular size and low
238
molecular weight. In this way, polar attractive forces are established between the plasticizer and
239
chain segments, which are responsible for the reduction of Tg point and simultaneously,
240
enhancement of chain segment mobility with better flexibility and processibility of the matrix
241
(Chin & Te, 2008; Forssell et al., 1997; Raj, Siddaramaiah, & Somashekar, 2004).
242
The hydroxyl groups are hydrogen bonding quarters on the investigated plasticizers (Fig. 1)
243
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
245
significantly drops the Tg point in Table 3. The Tg points shift significantly to lower temperature
246
region in DSC data presented in Fig. 3.
247
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248 249 250
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
251
Unlike xylitol and mannitol, the Tg points continue decreasing in the presence of 15 wt% and 25
252
wt% 1,4-butanediol, 1,2,6-hexanetriol and pentaerythritol as a result of increasing number of
253
available hydroxyl groups. However, Tg points do not significantly decrease in the samples
254
containing 15 wt% xylitol and mannitol. Only for xylitol, increase in its mass ratio to 25 wt%
255
leads to additional increase in segment mobility and decrease in Tg point down to 46.6oC.
13 Page 13 of 24
The observed different plasticizing efficiencies of xylitol and mannitol can be attributed to their
257
molecular structures. Compared to 1,4-butanediol, 1,2,6-hexanetriol and pentaerythritol, they are
258
relatively larger molecules with 5 and 6 hydroxyl groups, respectively. Probably, further
259
penetration into chain segments of PVA and starch is prevented due to their larger molecular
260
geometry after the initial plasticization of 5 wt% addition. Consequently, it can be mentioned that
261
mannitol molecules tend to interact with each other and do not significantly improve the thermal
262
properties of the blend, whereas smaller xylitol molecules can further play role in plasticization
263
when they are found in high amount.
264
3.2.2 Thermal-decomposition behaviors and thermogravimetric analyses
265
In the given figures, three distinct regions of mass loss can be seen. There are generally three
266
distinct mass loss regions in PVA:starch samples reported in literature. The first region (between
267
75oC and 200oC) is attributed to the loss of loosely bound water, accompanied by the formation
268
of volatile disintegrated products such as dislocation of the plasticizers in the blend. The second
269
region is described as the main decomposition step and the final stage is the carbonization of the
270
organic matter (above 500oC) (Galdeno et al., 2009; Luo, X., Li, J., & Lin, X, 2012; Saiah et al.,
271
2009; Shi et al., 2011). The thermal decomposition behaviors of various PVA:starch films
272
with/without polyol-based plasticizers are given in Fig. 4.
273
In addition to the overlapped thermal decomposition curves in Fig. 4, the thermal decomposition
274
data are also tabulated in Table 4 to present the 10 % weight loss temperature and residual
275
weights at 300oC, 400oC and 500oC for reference samples (starch, PVA, PVA:starch) and 15 wt%
276
polyol-based plasticizer containing samples.
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277 278 279 14 Page 14 of 24
280
Table 4. Thermal decomposition values of the samples with 15 wt% plasticizer Residual weight percentage at 400oC
at 500oC
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
cr
ip t
at 300 C
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Starch PVA PVA:Starch PSG-B15 PSG-H15 PSG-P15 PSG-X15 PSG-M15
o
us
Abbreviation
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
285
resistive cyclic hemiacetal in starch structure and development of blending towards high-energy
286
stability of the mixture (Sin et al., 2011). Therefore, PVA:starch sample has closer 10 %
287
decomposition temperature to gelatinized neat starch instead of PVA and less weight loss than
288
neat PVA at 300oC, 400oC and 500oC compared to PVA.
289
When the thermal decomposition data of polyol-based plasticizer containing samples are
290
examined, reductions in thermal resistivity are generally observed, except for mannitol containing
291
sample, compared to the PVA:starch sample. Although the mass loss order of different
292
plasticizers is attributed to their volatility difference in literature (Ma, Yu, & Wan, 2006), the
293
mass loss order of samples containing different plasticizers is also related to intermolecular
294
interactions and mobility between the plasticizer, PVA and starch chains according to the
295
interpreted data below.
296
As PVA:starch sample has closer thermal stability to starch due to the development of blending
297
towards high-energy stability, it is expected that higher the plasticization effect, lower the thermal
298
stability of the blend sample.
299
Other than the exception of 1,4-butanediol and 1,2,6-hexanetriol containing samples, the
300
increasing hydroxyl number and molecular size of the plasticizer enhance the thermal stability
301
with a maximum in the presence of mannitol. Although the increase in molecular size of the
302
plasticizers decreases their penetration ability into PVA and starch chain segments and limit the
303
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
305
high-energy stability. The exceptional behavior of 1,4-butanediol and 1,2,6-hexanetriol
306
containing samples might be attributed to their volatility difference. Therefore, the thermal
307
stability of PVA:starch:plasticizer samples is related to not only the volatility difference of the
308
plasticizers, but also to the mobility between the plasticizer, PVA and starch chains.
309
The mannitol containing sample shows better thermal endurance than neat starch and PVA:starch
310
samples at 300 oC and its 10 % weight loss temperature is at 298.7 oC, which is the highest
311
among the analyzed samples. However, its decomposition rate later gets higher and at 400oC and
312
500oC, the neat PVA:starch sample is distinguished as the most durable sample with 33.16 % and
313
20.85 % of remaining weight, respectively.
314
4. Conclusion
315
As a result of the increasing reservations in environmental and health issues, development of new
316
biodegradable products attracts attention of researchers. However, biodegradable polymers
317
cannot be solely used and must be blended with other biodegradable additives to enhance their
318
mechanical properties and shape stability. Although the properties of PVA:starch blend films
319
containing different plasticizers have been investigated in literature, new plasticizers are still
320
needed for better thermoplastic processability of the blends in production scale. In this sense,
321
several polyol-based plasticizers have been investigated in different mass ratios for gelatinized
322
PVA:starch blend films.
323
5 wt% addition of the investigated plasticizers lowers the Tg point significantly, and different
324
plasticizing behaviors are observed with increasing plasticizer amount. The observed decrease
325
continue in a descending manner with 15 wt% 1,4-butanediol, 1,2,6-hexanetriol and
326
pentaerythritol addition. Xylitol leads to additional increase in segment mobility with 25 wt%
327
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
329
into chain segments after the initial plasticization of 5 wt% addition.
330
The thermal decomposition data of polyol-based plasticizer containing samples indicate that
331
thermal resistivity is generally lower than neat PVA:starch blend film samples. However, the
332
orders of the plasticizers according to the 10 % weight loss temperature and residual weight
333
percentages at 300 oC generally indicate that the increasing hydroxyl number and molecular size
334
of the plasticizer enhance the thermal stability with a maximum in the presence of mannitol.
335
Based on the reported data, it can be consequently stated that although the number of hydrogen
336
groups on plasticizers are hydrogen bonding quarters for starch and PVA, molecular structure and
337
molecular geometry of plasticizers can prevent their penetration into chain segments and reduce
338
the intermolecular interactions, which in turn limit the expected plasticizing effect. Among the
339
investigated polyol-based plasticizers, 1,4-butanediol shows the highest plasticizing effect for
340
PVA:starch. It reduces the Tg point by approximately 27 oC, 31 oC and 39 oC, and 1,2,6-
341
hexanetriol reduces the Tg point by approximately 26 oC, 30 oC and 33 oC with 5 wt%, 15 wt%
342
and 25 wt% addition in the samples, respectively.
343
References
344
Arvanitoyannis, I., Kolokuris, I., Nakayama, A., Yamamoto, N., & Aiba, S. (1997). Physico-
345
chemical studies of chitosan-poly (vinyl alcohol) blends plasticized with sorbitol and sucrose.
346
Carbohydrate Polymers, 34, 9-19.
347
Chen, L., Iman, S. H., Stein, T. M., Gordon, S. H., Hou, C. T., & Greene, R. V. (1997). Starch-
348
polyvinyl alcohol cast film-performance and biodegredation. Polymer Preprints, 37, 461-462.
349
Chin, A. L., & Te, H. K. (2008). Shear and elongational flow properties of thermoplastic
350
polyvinyl alcohol melts with different plasticizer contents and degrees of polymerization. Journal
351
of Materials Processing Technology, 200, 331-338.
Ac ce p
te
d
M
an
us
cr
ip t
328
18 Page 18 of 24
Cinelli, P., Chiellini, E., Gordon, L. S. H., & Chiellini, L. E. (2005). Characterization of
353
biodegredable composite films prepared from blends of poly(vinyl alcohol), cornstarch, and
354
lignocellulosic fibre. Journal of Polymer Environment, 13, 47-59.
355
Dean, K. M., DO, M. D., Petinakis, E., & Yu, L. (2008). Key interactions in biodegradable
356
thermoplastic
357
Composites Science and Technology, 68(6), 1453-1462.
358
Fang, J. M., Fowler, P. A., Tomkinson, J., & Hill, C. A. S. (2002). The preparation and
359
characterization of a series of chemically modified potato starch. Carbohydrate Polymers, 47,
360
245-252.
361
Forssell, P. M., Mikkila, J. M., Moates, G. K., & Parker, R. (1997). Phase and glass transition
362
behaviour of concentrated barley starch-glycerol-water mixtures, a model for thermoplastic
363
starch. Carbohydrate Polymers, 34, 275-282.
364
Galdeano, M. C., Grossmann, M. V. E., Mali, S., Bello-Perez, L. A., Garcia, M. A., & Zamudio-
365
Flores, P. B. (2009). Effects of production process and plasticizers on stability of films and sheets
366
of oat starch. Materials Science and Engineering: C, 29, 492–498.
367
Gross, R.A., & Kalra, B. (2002). Biodegradable polymers for the environment. Science, 297, 803-
368
807.
369
Jayasekara, R., Harding, I., Bowater, I., Christie, G. B. Y., Lonergan, G. T. J. (2003).
370
Biodegradation by composting of surface modified starch and PVA blended films. Journal of
371
Polymers and the Environment, 11, 49-56.
372
Kim, M. (2003). Evaluation of degradability of hydroxypropylated potato starch/polyethylene
373
blend films. Carbohydrate Polymers, 54, 173-181.
374
Kim, M., & Lee, S-J. (2002). Characteristics of crosslinked potato starch and starch-filled linear
375
low-density polyethylene films. Carbohydrate Polymers, 50, 331-337.
micro-
and
nanocomposites.
cr
alcohol)/montmorillonite
Ac ce p
te
d
M
an
us
starch/poly(vinyl
ip t
352
19 Page 19 of 24
Liu, Z. Q., Feng, Y., & Yi, X. S. (1999). Thermoplastic starch/PVAI compounds: Preparation,
377
processing and properties. Journal of Applied Polymer Science, 74, 2667-2673.
378
Luo, X., Li, J., & Lin, X. (2012). Effect of gelatinization and additives on morphology and
379
thermal behavior of corn starch/PVA blend films. Carbohydrate Polymers, 90, 1595-1600.
380
Ma, X. F., Yu, J. G., & Wan, J. J. (2006). Urea and ethanolamine as a mixed plasticizer for
381
thermoplastic starch. Carbohydrate Polymers, 64, 267-273.
382
Ma, X., Yu, J. (2004). The effects of plasticizers containing amide groups on the properties of
383
thermoplastic starch. Starch/Stärke, 56, 545–551.
384
Majdzadeh-Ardakani, K., & Nazari, B. (2010). Improving the mechanical properties of
385
thermoplastic starch/poly (vinyl alcohol)/clay nanocomposites. Composites Science and
386
Technology, 70, 1557-1563.
387
Nakayama, Y., Takatsuka, M., & Matsuda, T. (1999). Surface hydrogelation using photolysis of
388
dithiocarbamate or xanthate: Hydrogelation, surface fixation, and bioactive substance
389
immobilization. Langmuir, 15, 1667-1672.
390
Park, H., Chough, S., Yun, Y., & Yoon, S. (2005). Properties of starch/PVA blend films
391
containing citric acid as additive. Journal of Polymers and the Environment, 13(4), 375-382.
392
Pavlovic, S., & Brandao, P. R. G. (2003). Adsorption of starch, amylose, amylopectin and
393
glucose monomer and their effect on the flotation of hematite and quartz. Minerals Engineering,
394
16, 1117-1122.
395
Petersen, K., Nielsen, P.V., Bertelsen, G., Lawther, M., Olsen, M., Nilsson, N.H., & Mortensen,
396
G. (1999). Potential of biobased materials for food packaging. Trends in Food Science &
397
Technology, 10, 52-68.
398
Raj, B., Sidddaramaiah, S., & Somashekar, R. (2004). Structure-property relation in polyvinyl
399
alcohol/starch composites. Journal of Applied Polymer Science, 91, 630-635.
Ac ce p
te
d
M
an
us
cr
ip t
376
20 Page 20 of 24
Saiah, R., Sreekumar, P. A., Leblanc, N., & Saiter, J.-M. (2009). Structure and thermal stability
401
ofthermoplasticfilms basedon wheatflourmodifiedbymonoglyceride. Industrial Crops and
402
Products, 29, 241–247.
403
Shi, Q. F., Chen, C., Gao, L., Jiao, L., Xu, H. Y., & Guo, W. H. (2011). Physical and degradation
404
properties of binary or ternary blends composed of poly (lactic acid), thermoplastic starch and
405
GMA grafted POE. Polymer Degradation and Stability, 96, 175–182.
406
Shi, R., Bi, J., Zhang, Z., Zhu, A., Chen, D., Zhou, X., Zhang, L., & Tian, W. (2008). The effect
407
of citric acid on the structural properties and cytotoxicity of the polyvinyl alcohol/starch films
408
when molding at high temperature. Carbohydrate Polymers, 74, 763-770.
409
Sin, L. T., Rahman, W. A. W. A., Rahmat, A. R., & Mokhtar, M. (2011). Determination of
410
thermal stability and activation energy of polyvinyl alcohol–cassava starch blends. Carbohydrate
411
Polymers, 83, 303-305.
412
Sreedhar, B., Chattopadhyay, D. K., Karunakar, M. S. H., & Sastry, A. R. K. (2006). Thermal
413
and surface characterization of plasticized starch polyvinyl alcohol blends crosslinked with
414
epichlorohydrin. Journal of Applied Polymer Science, 101, 25-34.
415
Sreedhar, B., Sairam, M., Chattopadhyay, D. K., Syamala Rathnam, P. A., & Mohan Rao, D. V.
416
(2005). Thermal, mechanical and surface characterization of starch-poly(vinyl alcohol) blends
417
and borax-crosslinked films. Journal of Applied Polymer Science, 96, 1313-1322.
Ac ce p
te
d
M
an
us
cr
ip t
400
21 Page 21 of 24
Sreekumar, P. A., Al-Harthi, M. A., & De, S. K. (2012). Effect of glycerol on thermal and
419
mechanical properties of polyvinyl alcohol/starch blends. Journal of Applied Polymer Science,
420
123, 135-142.
421
Tang, X. Z., Alavi, S., & Herald, T. (2008). Effects of plasticizers on the structure and properties
422
of starch-clay nanocomposite films. Carbohydrate Polymers, 74, 552-558.
423
Tang, X., & Alavi, S. (2011). Recent advances in starch, polyvinyl alcohol based polymer blends,
424
nanocomposites and their biodegradability. Carbohydrate Polymers, 85, 7-16.
425
Vasile, C., Stoleriu, A., Popescu, M. C., Duncianu, C., Kelnar, I., & Dimonie, D. (2008).
426
Morphology and thermal properties of some green starch/poly (vinyl alcohol)/montmorillonite
427
nanocomposites. Cellulose Chemistry and Technology, 42(9-10), 549-568.
428
Wang, Y., Chang, C., & Zhang, L. (2010). Effects of Freezing/Thawing Cycles and Cellulose
429
Nanowhiskers
430
Macromolecular Materials and Engineering, 295, 137-145.
431
Weber, C.J., Haugaard, V., Festersen, R., & Bertelsen, G. (2002) Production and application of
432
biobased packaging materials for the food industry. Food Additives & Contaminants, 19, 172-
433
177.
434
Wolkers, W. F., Oliver, A. E., Tablin, F., & Crowe, J. H. (2004). A Fourier-transform infrared
435
spectroscopy study of sugar glasses. Carbohydrate Research, 339 (6), 1077-1085.
436
Yin, Y., Li, J., Liu, Y., & Li, Z. (2005). Starch crosslinked with poly(vinyl alcohol) by boric acid.
437
Journal of Applied Polymer Science, 96, 1394-1397.
438
Yoon, S. D., Chough, S. H., & Park, H. R. (2006a). Properties of starch-based blend films using
439
citric acid as additive. Journal of Applied Polymer Science, 100, 2554-2560.
Structure
and
Properties
of
Biocompatible
Starch/PVA
Sponges.
Ac ce p
te
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M
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Yoon, S. D., Chough, S. H., & Park, H. R. (2006b). Effects of additives with different functional
441
groups on the physical properties of starch/PVA blend film. Journal of Applied Polymer Science,
442
100, 3733-3740.
443
Yoon, S. D. (2014). Cross-Linked Potato Starch-Based Blend Films Using Ascorbic Acid as a
444
Plasticizer. Journal of Agricultural and Food Chemistry, 62, 1755-1764.
445
Zhou, X. Y., Cu, Y. F., Jia, D. M., & Xie, D. (2009). Effect of a complex plasticizer on the
446
structure and properties of the thermoplastic PVA/starch blends. Polymer Plastics Technology
447
and Engineering, 48(5), 489-495.
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Highlights -
PVA:starch blend films were prepared using a series of polyol-based plasticizers
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5% (wt.) addition of the investigated plasticizers lowers the Tg point significantly
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Different plasticization behaviors are observed with increasing plasticizer amount
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Molecular geometry of plasticizers can prevent penetration into chain segments
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1,4-butanediol shows the highest plasticizing effect for PVA:starch
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