PLA Blends with Improved Processability and

Article pubs.acs.org/IECR

Thermoplastic PVA/PLA Blends with Improved Processability and Hydrophobicity Hong-Zhen Li, Si-Chong Chen,* and Yu-Zhong Wang* Center for Degradable and Flame-Retardant Polymeric Materials, College of Chemistry, State Key Laboratory of Polymer Materials Engineering, National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), Sichuan University, Chengdu, Sichuan Province, 610064, China ABSTRACT: A novel plasticizer (lacti-glyceride) synthesized by esterification of glycerol with L-lactic acid was developed for thermal processing of PVA/PLA blend. Meanwhile, the stannous octoate (Sn(Oct)2) was used as the catalyst for the transesterification reaction of PVA, PLA, and the plasticizer. The results showed that the PVA/PLA blends plasticized with lactiglyceride have improved thermal processability and mechanical properties compared to those plasticized with glycerol, because the lacti-glyceride may act not only as a plasticizer but also as a compatibilizer for PVA and PLA. SEM images indicated that PVA/PLA blends catalyzed with Sn(Oct)2 had better compatibility than those without catalyst. Water contact angle measurements showed that the PVA/PLA blends plasticized with lacti-glyceride have much more hydrophobic surfaces than those blends plasticized with glycerol. The blends will find wider applications than PVA.

1. INTRODUCTION Poly(vinyl alcohol) is a synthetic polymer with good flexibility,1 transparency,2 toughness,3 biocompatibility,4 barrier properties,5 nontoxicity,6 and biodegradability7−9 and has been widely used in various fields such as biomedicine,10,11 packaging industry,12 pharmacy,11,13 and biosensors.14 However, it is difficult to produce the PVA film through melt processing because its melting temperature is too close to its decomposition temperature. What is worse, PVA has a poor water resistance. These drawbacks limit its wider application, especially as a food-packaging film.15 In order to solve these problems, modifications of PVA have been conducted, including melt blending with various polymers, such as starch,16−19 collagen hydrolysate,20,21 lignin,22 chitosan,23 and poly(3-hydroxybutyrate).24 Melt blending in extruder is the most cost-effective strategy for commercial scale production of polymeric blend based on PVA. However, it is difficult to produce the PVA film through melt processing because its Tm is too close to its Td. A plasticizer is defined as “a substantially nonvolatile, high boiling, nonseparating substance, which when added to another material changes the physical and/or mechanical properties of that material”.25 The addition of plasticizer may reduce PVA’s melting temperature, enhance film flexibility, decrease brittleness, avoid shrinking during handling and storage, and therefore make it easier for film to be peeled off from the support during manufacturing.26−28 Some new plasticizers have been used in PVA blends in recent years. The mixture of glycerol and urea were used as a complex plasticizer for the thermoplastic PVA/starch blends by Zhou et al.,16 which could form more stable and strong hydrogen bonds with the hydroxyl group of PVA/starch molecules than that with the conventional plasticizer, glycerol. Poly(ethylene glycol)-bis(carboxymethyl) ether (PEGBCME) was used as a plasticizer in PVA/PAMPS blends by Qiao et al.,29 and the double carboxylic acid end groups in PEGBCME might contribute to the high proton conduction of the membranes in addition to the sulfonic acid groups in PAMPS; while processability, © XXXX American Chemical Society

mechanical properties, and hydrophilicity are still the main obstacles for PVA blended films in various application fields. However, conventional water-soluble plasticizers for PVA, such as glycerol and formamide, will induce severe moisture absorption that might negatively affect the performance of PVA materials during their applications.28,30 Therefore, it is very important to design a facile method for preparing PVA blends with acceptable thermal processability, mechanical properties, and hydrophobicity. In this work a novel plasticizer, lacti-glyceride, was designed for thermal processing of PVA/PLA blends. The hydroxyl groups of lacti-glyceride may help to plasticize PVA by hydrogen-bonding interaction between PVA and the plasticizer,31 while the lactyl units of the plasticizer may also help to improve the compatibility between PVA and PLA. What is more, the hydrophobicity of the lacti-glyceride plasticized PVA increased obviously comparing to neat PVA or PVA plasticized by glycerol because of the esterification bonds of the lactiglyceride, which is in favor of avoiding a series of problems caused by moisture during use.

2. EXPERIMENTAL SECTION 2.1. Materials. PVA (PVA-1799, degree of polymerization 1700, degree of hydrolysis 99%) was obtained from Yunwei Company (Qujing City, Yunnan Province, China) and was rigorously dried at 80 °C in vacuo until a constant weight was obtained and then stored in a desiccator under vacuum at room temperature over P2O5. Poly(lactic acid) (PLA), 4032 D, was purchased in pellet form from Natureworks Co., Minnetonka, USA. L-Lactic acid as an 88% aqueous solution was supplied by National Chemical Industry (Guangshui City, Hubei Province, Received: June 23, 2014 Revised: October 14, 2014 Accepted: October 17, 2014

A

dx.doi.org/10.1021/ie502531w | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

Article

Scheme 1. Synthesis of Lacti-Glyceride

concentration, 15% (w/v); internal standard, tetramethylsilane (TMS); and temperature, 25 °C. 2.7. Thermal Analysis. DSC measurement was conducted under nitrogen atmosphere using TA DSC Q100 in sealed aluminum pans, relative to indium and gallium standards. The samples, which were dried at 80 °C prior to test, were heated from 25 to 120 °C at a heating rate of 10 °C/min (first heating scan). The glass transition temperature (Tg) was determined from the first heating scan. 2.8. Tensile Tests. Tensile tests were carried out according to ASTM D638, type III with a crosshead speed of 50 mm/min with a universal test machine (CMT4104, Shenzhen SANS Testing Machine Co., China). The sample films (0.4−0.5 mm thickness) were stored at 50% relative humidity (RH) and 25 °C before testing. 2.9. Scanning Electron Microscope. The morphologies of the samples were observed by a JSM-5900 (JEOL, Japan) scanning electron microscopy (SEM) with an accelerating voltage of 10 kV. All the samples were brittlely fractured in liquid nitrogen and then etched in chloroform to remove the residual PLA from the fractured surfaces, and the surfaces were coated with a layer of gold. 2.10. Melt Flow Rate (MFR) Measurement. The melt flow rates of the samples were recorded by melt flow rate meter (XNR-400AM, Chengdeshi Shipeng Detection Equipment Co., Ltd., China). The load and temperature for measurement were 3.045 kg and 200 °C, respectively. 2.11. Water Contact Angle (WCA) Measurement. A contact angle analyzer (Model JC2000D2H, China) was used to measure the contact angle of the probe liquids (water) in air on the surface of sample sheets. The sample sheets were glued to a movable sample stage horizontally; then about 4 μL of probe liquid was dropped on the surface of the sheet using a micro syringe. The advancing contact angle was measured by advancing a small volume of decane droplet (typically 5 μL) onto the surface, using a microsyringe. The receding contact angle was measured by slowly removing the liquid from a drop already on the surface. For each sample a minimum of four different readings were recorded.

China) and used without further treatment. Analytical grade toluene and glycerol and p-toluenesulfonic acid were purchased from Kelong Chemical Factory (Chengdu City, Sichuan Province, China) and used without further purification. Stannous octoate (Sn(Oct)2) was purchased from Sigma (USA) and was used without any further purification. 2.2. Preparation of Lacti-Glyceride. A certain amount of L-lactic acid, glycerol, p-toluenesulfonic acid, and toluene were added into a boiling flask-3-necked quipped with a water segregator and heated to 105 °C with continuous stirring for 4 h. After the reaction, reduced pressure distillation was carried out to remove the residual toluene and L-lactic acid, and a mixture of lacti-glyceride in liquid state with different degree of substitutions was obtained. 2.3. Preparation of Lacti-Glyceride Plasticized PVA. PVA and lacti-glyceride were mixed with a mass ratio of 7:3 in a high-speed mixer, and then the mixture was placed in a drying oven at 110 °C for 1 h. Then the mixture was melt extruded through a twin-screw extruder. Plasticized PVA with lactiglyceride was marked as l-PVA, and all l-PVA samples with a certain amount of lacti-glyceride were expressed as 1-PVA(x%), where x% is the content of lacti-glyceride in 1-PVA. As a comparison, PVA plasticized with glycerol was prepared in the same way as described above and was marked as g-PVA. 2.4. Preparation of Thermoplastic Blends of PVA/PLA. l-PVA(30%) and PLA were blended with a twin-screw extruder, at 190 °C and screw rotation rate was 60 rpm, with a certain amount of Sn(Oct)2 as a catalyst for transesterification between 1-PVA and PLA. l-PVA/PLA films for measurements were prepared by using a hot-pressing apparatus. All of the samples followed the same processing procedure: after the samples were preheated at 190 °C for 10 min, pressure was applied and quickly reached 10 MPa, which was maintained for 10 min. To maintain the film shape during cooling process, the obtained lPVA/PLA film was quickly cold-pressed at 25 °C and 15 MPa for 5 min as soon as the pressure was released. As a comparison, g-PVA/PLA blends were prepared in the same way as described above. 2.5. ESI-MS Analysis. Mass spectra were acquired on a quadrupole ion trap time-of-flight mass spectrometer (LCMSIT-TOF, Shimadzu, Kyoto, Japan) equipped with an ESI source at a mass resolution of 10,000. 2.6. 1H NMR Analysis. 1H NMR experiments were performed on a Varian Inova 400 operating at 400 MHz. The measuring conditions were as follows: solvent, D2O; solute

3. RESULTS AND DISCUSSION 3.1. Preparation and Characterization of LactiGlyceride. Esterification of glycerol with L-lactic acid was performed by using p-toluenesulfonic acid as a catalyst (Scheme 1). Mass spectrometry of the product of the esterification reaction was recorded as shown in Figure 1. Three major mass B



Article

Figure 1. High-resolution mass spectrum of lacti-glyceride.

peaks at 187, 259, and 331 were observed corresponding to mono-, di-, and trisubstitution derivatives, respectively. This result suggested that the lactic acid can randomly react with any of the three hydroxyl groups of the glycerol. Therefore, a mixture of mono-, di-, and trisubstitution derivatives was obtained. Figure 2 shows the typical 1H NMR spectrum of lactiglyceride. Comparing to 1H NMR spectra of glycerol and L-

Figure 3. Effect of degree of substitution (Ds) of hydroxyl groups in lacti-glyceride on the tensile strength and elongation at break of lPVA(30%).

Figure 4. It can be seen from Figure 3 that when Ds varied from 0.94 to 1.89, the tensile strength and elongation at break had no obvious change. However, when Ds increased to 2.0, the tensile property of the sample decreased obviously. This phenomenon suggested that the plasticizer with high Ds may have poor intermolecular interaction with PVA. Meanwhile, Figure 4 indicates that when Ds = 1.58, the sample shows the highest melt flow rate. Therefore, the lacti-glyceride with Ds = 1.58 was used in this work. 3.2. Preparation and Characterization of LactiGlyceride Plasticized PVA. Plasticized PVA was prepared by a melt extrusion process through a twin-screw extruder using lacti-glyceride as the plasticizer. Table 1 shows the glass transition temperatures (Tg) of l-PVA with various content of lacti-glyceride. It can be seen that with the increase of lactiglyceride in 1-PVA, a decrease of Tg was observed, which was caused by the effective plasticization of lacti-glyceride. The effect of lacti-glyceride content on the mechanical properties of l-PVA is shown in Figure 5. The tensile strength of l-PVA decreased while the elongation at break increased with the addition of lacti-glyceride, which was caused by the intermolecular interaction between PVA and lacti-glyceride.

Figure 2. 1H NMR spectra of glycerol, L-lactic acid, and lacti-glyceride.

lactic acid, some new chemical shifts were observed at 4.1 and 3.8 ppm, which could be attributed to the methylene and methine groups of the esterified glycerols with different degrees of esterification, respectively. The intensity of the methyl groups (I1.3) of lactic acid moieties and the methylene groups (I4.1 and I3.4−3.5) of glycerol moieties could be used to calculate the degree of substitution of hydroxyl groups in lacti-glyceride (Ds) by the following equation: I1.3 × 4 Ds = (I4.1 + I3.5) × 3 (1) Tensile properties and MFR of l-PVA(30%) plasticized by lacti-glyceride with different Ds were presented in Figure 3 and C



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Figure 6. Effect of lacti-glyceride content on the melt flow rate of lPVA.

Figure 4. Effect degree of substitution (Ds) of hydroxyl groups in lactiglyceride on the melt flow rate of l-PVA(30%).

Table 1. Tg of l-PVA with Various Content of LactiGlyceride sample

content of lacti-glyceride (%)

Tg (°C)

l-PVA(15%) l-PVA(20%) l-PVA(25%) l-PVA(30%) l-PVA(35%)

15 20 25 30 35

59.32 57.56 56.90 55.16 53.43

3.3. Melt Blending and Characterization of PVA and PLA. PLA is aliphatic polyester with excellent biodegradability, biocompatibility, processability, and mechanical strength, which has the potential to replace conventional petrochemical-based polymers. Therefore, blended PVA with a renewable and abundant agro-resource based such as PLA can be utilized to improve the material performance such as environmental friendship, thermoplasticity, and the mechanical properties. The blends of plasticized PVA and PLA were prepared by melting extrusion using Sn(Oct)2 as a catalyst. As a comparison, PVA/ PLA blends using neat glycerol as a plasticizer were also prepared in the same way. Tensile strength and elongation at break of l-PVA(30%), g-PVA/PLA, and l-PVA/PLA blends with different compositions are presented in Figure 7. With the increase of PLA content, the tensile strength of l-PVA/PLA increased slightly from 35.4 to 39.6 MPa, while the elongation at break decreased from 248% to 216%, which could be attributed to the relatively high rigidity and low flexibility of PLA.

Figure 5. Effect of lacti-glyceride content on the tensile strength and elongation at break of l-PVA.

Figure 6 shows the MFR (melt flow rate) of l-PVA with different content of lacti-glyceride. The MFR of l-PVA sharply increased from 0.07 g/10 min to 3.05 g/10 min with the addition of lacti-glyceride. The addition of the plasticizer may weaken the hydrogen bonding in the polymer by establishing new intermolecular interactions with the hydroxyl groups of PVA.32 The mobility of PVA molecules were improved by the plasticizer and resulted in a decreased entanglement concentration. Therefore, the amount of plasticizer had very important influence on the properties of the plasticized PVA. In this work, plasticized PVA with 30% content of lacti-glyceride was used in the following study in consideration of the balance of processability and mechanical properties.

Figure 7. Tensile strength and elongation at break of l-PVA(30%) and blends of PLA and plasticized PVA with different PLA contents using stannous octoate as the catalyst. D



Article

Figure 8. SEM images of fracture surfaces of l-PVA/PLA-8:2 with (left) and without (right) catalysis by Sn(Oct)2 after etched by chloroform.

Compared to PVA/PLA blends using glycerol as a plasticizer, the blends with the same PLA content using lacti-glyceride as a plasticizer had a larger tensile strength, which can be explained by the different plasticization effect of glycerol and lactiglyceride on the PVA/PLA blends. Plasticizers, such as glycerol and lacti-glyceride in this work, plasticize effectively due to their ability to reduce internal hydrogen bonding while increasing intermolecular spacing of PVA molecules.33 However, the lactiglyceride may also enhance the compatibility between PVA and PLA since it has both hydroxyl groups and lactic acid ester groups, resulting in enhanced tensile strength and relatively high toughness. The application of the catalyst for transesterification reaction could also improve the compatibility of PVA and PLA in the blends. Figure 8 shows SEM images of fracture surfaces of lPVA/PLA-8:2 with and without using Sn(Oct)2 as a catalyst. Chloroform was used for selectively removing the PLA phase of the blends. Therefore, many small holes were observed on the fractured surfaces. The hole size of the blend using Sn(Oct)2 as a catalyst is obviously smaller than that of the blend without a catalyst, suggesting that the compatibility of PVA and PLA in this sample was improved. This phenomenon could be attributed to the copolymer obtained by the in situ transesterification reaction between PVA and PLA, which may act as a compatibilizer for the blend. Figure 9 presents the typical DSC thermograms of lPVA(30%) and l-PVA/PLA blends, and their glass transition temperatures (Tg) are listed in Table 2. As shown in Figure 9 and Table 2, all l-PVA(30%) and l-PVA/PLA samples exhibited clear and single Tg, because the Tg of PVA and PLA are very close. Moreover, the Tg of l-PVA/PLA blends decreased with the increase of PLA content. It is well-known that the addition of the plasticizer leads to a decrease in intermolecular forces along polymer chains which improves the flexibility and chain mobility,34 and the Tg decreases with the addition of the plasticizer in the case of hydrophilic polymers.35−37 The Tg of PVA/PLA blends are smaller than 1-PVA and neat PLA, which could be attributed to the addition of Sn(Oct)2 during blending. Owing to the transesterification reaction between lPVA(30%), PLA, and the lacti-glyceride catalyzed by Sn(Oct)2, both lacti-glyceride and the copolymer obtained by the in situ transesterification may act as a compatibilizer in blends of PVA and PLA. The interaction between PLA and PVA at the interface of the two phases may increase the flexibility and chain mobility of the polymers. Moreover, the transesterifica-

Figure 9. DSC curves of PLA, l-PVA(30%), and blends of PLA and plasticized PVA with different PLA contents.

Table 2. Differences of Tg between l-PVA(30%), PLA, and lPVA/PLA Blends with Different Mass Ratios of PVA and PLA sample

mass ratio of PVA:PLA

Tg (°C)

l-PVA(30%) l-PVA/PLA-9:1 l-PVA/PLA-8:2 l-PVA/PLA-7:3 PLA

9:1 8:2 7:3

55.16 54.95 54.31 50.29 61.63

tion may also decrease the regularity of the PVA chains and the molecular weight of the PLA chains as well as their intermolecular reactions and therefore resulted in a decrease of Tg of PVA/PLA blends compared to l-PVA(30%) and neat PLA. MFR results of l-PVA(30%) and l-PVA/PLA blends are displayed in Figure 10. It can be seen from the graph that the MFR of PVA/PLA blends with various content of PLA was much higher than l-PVA(30%) and g-PVA/PLA. The results indicated that l-PVA/PLA blends had enhanced melting processability, which can also be explained by the compatibilization effect of lacti-glyceride on PVA/PLA blends. Surface hydrophobicity is a very important property for PVAbased materials used in daily applications such as food E



Article

Figure 12. Δθ (contact angle hysteresis) of films of pure PVA, lPVA(30%), and blends of PLA and plasticized PVA with different PLA contents.

Figure 10. Melt flow rate of l-PVA(30%) and blends of PLA and plasticized PVA with different PLA contents.

packaging films, which will limit its applications as films in high humidity.28,38 Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. Therefore, the addition of a large amount of glycerol to PVA as a plasticizer may inevitably increase the surface hydrophilicity of the PVA based materials. The surface hydrophobicity of the samples with different compositions was evaluated by water contact angle tests. Figure 11 and Figure 12 separately show the

esterification of glycerol obviously decreased its hydrophilicity. The contact angle hysteresis is the difference between the apparent advancing and receding contact angles and is a measure of the “stickiness” of a surface, i.e., the resistance to motion, experienced by a droplet as it rolls off a surface.39−41 It can be seen from Figure 12 that all the l-PVA(30%) and l-PVA/ PLA films had surfaces with strong adhesion, while as PLA was introduced to the system, the adhesion property showed a decline. As to the pure PVA and g-PVA/PLA films, they had a very low Δθ because of their strong hydrophilicity.

4. CONCLUSIONS A novel plasticizer, lacti-glyceride, was designed for thermal processing of PVA/PLA blend. The molecular structure of the plasticizer was characterized and confirmed by ESI-MS and NMR. The PVA/PLA blends plasticized with lacti-glyceride have the improved thermal processability and mechanical properties compared to those plasticized with glycerol, suggesting that the lacti-glyceride may act not only as a plasticizer but also as a compatibilizer for PVA and PLA. Water contact angle measurements showed that the PVA/PLA blends plasticized with lacti-glyceride have much more hydrophobic surfaces than those blends plasticized with glycerol, indicating that the esterification of glycerol by L-lactic acid obviously decreased the moisture absorption ability of the blends.

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AUTHOR INFORMATION

Corresponding Authors

Figure 11. Water contact angles of PVA, l-PVA(30%), and blends of PLA and plasticized PVA with different PLA contents.

*Phone: 86-28-85410755. Fax: 86-28-85410755. E-mail: [email protected]. *E-mail: [email protected].

water contact angles and contact angle hysteresis (Δθ) of films of pure PVA, l-PVA(30%), and blends of PLA and plasticized PVA with different PLA contents. Neat PVA films have obvious hydrophilic surfaces because it is a water-soluble polymer. When plasticized with glycerol, g-PVA/PLA blend films showed more hydrophilic surface than neat PVA even after the hydrophobic PLA was introduced to PVA blends. As a contrast, l-PVA(30%) and its blends with PLA had a much more hydrophobic surface than neat PVA, indicating that the

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 51121001), the Program for Changjiang Scholars and Innovative Research Team in University of Chinese Ministry of Education (IRT1026), and F



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hydrolysate thermoplastic blends: I. Experimental design optimization and biodegradation behaviour. Polym. Test. 2003, 22, 801. (21) Alexy, P.; Bakoš, D.; Crkoňová, G.; Kramárová, Z.; Hoffmann, J.; Julinová, M.; Chiellini, E.; Cinelli, P. Poly(vinyl alcohol)−collagen hydrolysate thermoplastic blends: II. Water penetration and biodegradability of melt extruded films. Polym. Test. 2003, 22, 811. (22) Kubo, S.; Kadla, J. F. The formation of strong intermolecular interactions in immiscible blends of poly(vinyl alcohol)(PVA) and lignin. Biomacromolecules 2003, 4, 561. (23) Arvanitoyannis, I.; Kolokuris, I.; Nakayama, A.; Yamamoto, N.; Aiba, S.-i. Physico-chemical studies of chitosan-poly(vinyl alcohol) blends plasticized with sorbitol and sucrose. Carbohydr. Polym. 1997, 34, 9. (24) Olkhov, A. A.; Vlasov, S. V.; Iordanskii, A. L.; Zaikov, G. E.; Lobo, V. M. M. Water transport, structure features and mechanical behavior of biodegradable PHB/PVA blends. J. Appl. Polym. Sci. 2003, 90, 1471. (25) Banker, G. S. Film coating theory and practice. J. Pharm. Sci. 1966, 55, 81. (26) Guilbert, S.; Gontard, N.; Gorris, L. G. M. Prolongation of the shelf-life of perishable food products using biodegradable films and coatings. LWT–Food. Sci. Technol. 1996, 29, 10. (27) Bastioli, C.; Bellotti, V.; Del Tredici, G.; Ponti, R. Method of producing plasticized polyvinyl alcohol and its use for the preparation of starch-based, biodegradable thermoplastic compositions. U.S. Patent, 5462981, 1995. (28) Tang, X. Z.; Alavi, S. Recent advances in starch, polyvinyl alcohol based polymer blends, nanocomposites and their biodegradability. Carbohydr. Polym. 2011, 85, 7. (29) Qiao, J. L.; Ikesaka, S.; Saito, M.; Kuwano, J.; Okada, T. Life test of DMFC using poly(ethylene glycol)bis(carboxymethyl)ether plasticized PVA/PAMPS proton-conducting semi-IPNs. Electrochem. Commun. 2007, 9, 1945. (30) Liu, Z. Q.; Feng, Y.; Yi, X. S. Thermoplastic starch/PVAl compounds: preparation, processing, and properties. J. Appl. Polym. Sci. 1999, 74, 2667. (31) Jang, J.; Lee, D. K. Plasticizer effect on the melting and crystallization behavior of polyvinyl alcohol. Polymer 2003, 44, 8139. (32) Ghebremeskel, A. N.; Vemavarapu, C.; Lodaya, M. Use of surfactants as plasticizers in preparing solid dispersions of poorly soluble API: selection of polymer−surfactant combinations using solubility parameters and testing the processability. Int. J. Pharm. 2007, 328, 119. (33) Lieberman, E. R.; Gilbert, S. G. Gas permeation of collagen films as affected by cross-linkage, moisture, and plasticizer content. J. Polym. Sci. Polym. Symp. 1973, 41, 33. (34) da Silva, M. A.; Bierhalz, A. C. K.; Kieckbusch, T. G. Alginate and pectin composite films crosslinked with Ca2+ ions: Effect of the plasticizer concentration. Carbohydr. Polym. 2009, 77, 736. (35) Linhardt, F. Temperaturabhängigkeit des Elastizitätsmoduls von Weich-PVC-Massen. Kunststoffe 1963, 53, 18. (36) Illers, V. K. H. Der Einfluß von Wasser auf die molekularen Beweglichkeiten von Polyamiden. Makromol. Chem. 1960, 38, 168. (37) Sakurai, K.; Maegawa, T.; Takahashi, T. Glass transition temperature of chitosan and miscibility of chitosan/poly(N-vinyl pyrrolidone) blends. Polymer 2000, 41, 7051. (38) Zhao, G. H.; Liu, Y.; Fang, C. L.; Zhang, M.; Zhou, C. Q.; Chen, Z. D. Water resistance, mechanical properties and biodegradability of methylated-cornstarch/poly(vinyl alcohol) blend film. Polym. Degrad. Stab. 2006, 91, 703. (39) Quéré, D. Non-sticking drops. Rep. Prog. Phys. 2005, 68, 2495. (40) Dussan V, E.; Chow, R. T.-P. On the ability of drops or bubbles to stick to non-horizontal surfaces of solids. J. Fluid. Mech. 1983, 137, 1. (41) Reyssat, M.; Quéré, D. Contact Angle Hysteresis Generated by Strong Dilute Defects. J. Phys. Chem. B 2009, 113, 3906.

the High-Tech Research & Development Program (Contract No. 2012AA062904).

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REFERENCES

(1) Julinová, M.; Dvořać ǩ ová, M.; Kupec, J.; Hubácǩ ová, J.; Kopčilová, M.; Hoffmann, J.; Alexy, P.; Nahálková, A.; Vašková, I. Influence of technological process on biodegradation of PVA/WAXY starch blends in an aerobic and anaerobic environment. J. Polym. Environ. 2008, 16, 241. (2) Podsiadlo, P.; Kaushik, A. K.; Arruda, E. M.; Waas, A. M.; Shim, B. S.; Xu, J.; Nandivada, H.; Pumplin, B. G.; Lahann, J.; Ramamoorthy, A.; Kotov, N. A. Ultrastrong and stiff layered polymer nanocomposites. Science 2007, 318, 80. (3) Wu, W. Q.; Tian, H. F.; Xiang, A. X. Influence of Polyol Plasticizers on the Properties of Polyvinyl Alcohol Films Fabricated by Melt Processing. J. Polym. Environ. 2012, 20, 63. (4) Paradossi, G.; Cavalieri, F.; Chiessi, E.; Spagnoli, C.; Cowman, M. K. Poly(vinyl alcohol) as versatile biomaterial for potential biomedical applications. J. Mater. Sci.: Mater. Med. 2003, 14, 687. (5) DeMerlis, C. C.; Schoneker, D. R. Review of the oral toxicity of polyvinyl alcohol (PVA). Food Chem. Toxicol. 2003, 41, 319. (6) Oviedo, I. R.; Méndez, N. A. N.; Gómez, M. P. G.; Rodríguez, H. C.; Martinez, A. R. Design of a physical and nontoxic crosslinked poly(vinyl alcohol) hydrogel. Int. J. Polym. Mater. 2008, 57, 1095. (7) Finch, C. A. Polyvinyl alcohol: developments; Wiley: New York, 1992. (8) Chiellini, E.; Corti, A.; Solaro, R. Biodegradation of poly(vinyl alcohol) based blown films under different environmental conditions. Polym. Degrad. Stab. 1999, 64, 305. (9) Corti, A.; Solaro, R.; Chiellini, E. Biodegradation of poly(vinyl alcohol) in selected mixed microbial culture and relevant culture filtrate. Polym. Degrad. Stab. 2002, 75, 447. (10) Costa-Júnior, E. S.; Barbosa-Stancioli, E. F.; Mansur, A. A. P.; Vasconcelos, W. L.; Mansur, H. S. Preparation and characterization of chitosan/poly(vinyl alcohol) chemically crosslinked blends for biomedical applications. Carbohydr. Polym. 2009, 76, 472. (11) Mc Gann, M. J.; Higginbotham, C. L.; Geever, L. M.; Nugent, M. J. D. The synthesis of novel pH-sensitive poly(vinyl alcohol) composite hydrogels using a freeze/thaw process for biomedical applications. Int. J. Pharm. 2009, 372, 154. (12) Sapalidis, A. A.; Katsaros, F. K.; Romanos, G. E.; Kakizis, N. K.; Kanellopoulos, N. K. Preparation and characterization of novel poly(vinyl alcohol)−Zostera flakes composites for packaging applications. Composites, Part B 2007, 38, 398. (13) Nugent, M. J. D.; Higginbotham, C. L. Preparation of a novel freeze thawed poly(vinyl alcohol) composite hydrogel for drug delivery applications. Eur. J. Pharm. Biopharm. 2007, 67, 377. (14) Ren, G. L.; Xu, X. H.; Liu, Q.; Cheng, J.; Yuan, X. Y.; Wu, L. L.; Wan, Y. Z. Electrospun poly(vinyl alcohol)/glucose oxidase biocomposite membranes for biosensor applications. React. Funct. Polym. 2006, 66, 1559. (15) Ding, J.; Chen, S. C.; Wang, X. L.; Wang, Y. Z. Synthesis and properties of thermoplastic poly(vinyl alcohol)-graft-lactic acid copolymers. Ind. Eng. Chem. Res. 2008, 48, 788. (16) Zhou, X. Y.; Cui, Y. F.; Jia, D. M.; Xie, D. Effect of a complex plasticizer on the structure and properties of the thermoplastic PVA/ starch blends. Polym.-Plast. Technol. Eng. 2009, 48, 489. (17) Park, J. S.; Yang, J. H.; Kim, D. H.; Lee, D. H. Degradability of expanded starch/PVA blends prepared using calcium carbonate as the expanding inhibitor. J. Appl. Polym. Sci. 2004, 93, 911. (18) Yang, S. Y.; Huang, C. Y. Plasma treatment for enhancing mechanical and thermal properties of biodegradable PVA/starch blends. J. Appl. Polym. Sci. 2008, 109, 2452. (19) Zou, G. X.; Jin, P. Q.; Xin, L. Z. Extruded starch/PVA composites: Water resistance, thermal properties, and morphology. J. Elastomers Plast. 2008, 40, 303. (20) Alexy, P.; Bakoš, D.; Hanzelova, S.; Kukolikova, L.; Kupec, J.; Charvátová, K.; Chiellini, E.; Cinelli, P. Poly(vinyl alcohol)−collagen G


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