Facile fabrication of poly(vinyl alcohol) gels and derivative aerogels

A facile preparation of poly(vinyl alcohol) (PVOH) hydrogels and their derivative PVOH/montmorillonite clay aerogels is reported, using water as solvent and divinylsulfone as crosslinking agent, making use of an environmentally friendly freeze drying process. The materials exhibit significantly increased mechanical properties after crosslinking. The compressive modulus of an aerogel prepared from an aqueous suspension containing 2 wt% PVOH/8 wt% clay increased 29-fold upon crosslinking, for example. Crosslinking of the polymer/clay aerogels decreased the onset decomposition temperature as measured by thermogravimetric analysis, and generated a more continuous structure at higher clay contents. Such polymer/clay aerogels are promising materials for low flammability applications.     

Crosslinking of cotton in the presence of poly(vinyl alcohol). Analysis and composition of products

The spectrophotometric method developed by Finley for the determination of poly(vinyl alcohol) in paper coatings has been adapted for analysis of cotton fabrics crosslinked with finishes containing a poly(vinyl alcohol) additive. The effect of time and pH of hydrolysis on the analysis, and the dependency of the durability of the poly(vinyl alcohol) on the crosslinking agent are established. Evidence of chemical attachment to the cellulose of the cotton fiber through the crosslinking agent is offered.     

Measurement and simple equation models of the specific heats of neat and glycerol‐plasticized poly(vinyl alcohol)

The specific heats (C_sp) of neat and glycerol‐plasticized poly(vinyl alcohol) (PVOH) were studied by differential scanning calorimetry at 330–530 K. Glycerol‐plasticized poly(vinyl alcohol) was prepared by a melt‐blending method. The outcomes were modeled into mathematical functions. Incorporation of glycerol increased the specific heat of PVOH. Glycerol provided internal lubrication to the PVOH system, giving a smoother and lower‐amplitude melting curve. As a result, glycerol‐plasticized PVOH had a lower melting‐temperature range than neat PVOH. However, higher energy was required to increase the temperature of glycerol‐plasticized PVOH. The modeling functions showed a best fits regression range of 0.967–0.999. Neat PVOH and glycerol‐plasticized PVOH required 1166.05 J/g and 2113.09 J/g, respectively, to increase the temperature from 330 to 530 K. J. VINYL ADDIT. TECHNOL., 18:198–203, 2012. © 2012 Society of Plastics Engineers     

Incorporation of postconsumer polyurethane foam into a polymer/clay aerogel matrix

The feasibility of incorporating ground recycled polyurethane (PU) foam into clay/polymer aerogels was demonstrated, and a range of compositions were prepared and characterized to determine the effect of variation in the formulations on density and mechanical properties of the resulting materials. This study followed a modified combinatorial approach. Initially, experiments were performed in water using either sodium exchanged montmorillonite or laponite clay, poly(vinyl alcohol) (PVOH) solution as the polymer binder, and the recycled PU foam. Freezing and freeze‐drying the aqueous gels produced aerogels, which were characterized through density and mechanical testing, scanning electron microscopy, and thermal gravimetric analysis. The study was expanded by exploring alternative binder chemistries, including the use of an alginate polymer in place of the PVOH or adding a polyisocyanate as a crosslinking agent for PVOH. The effect of recycled PU foam content, clay type and level, and binder type and level on the mechanical properties of the aerogels were determined and will be discussed herein. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42586.     

聚乙烯醇/微纤化纤维素复合微发泡材料的制备

通过溶液浇铸法制备了聚乙烯醇(PVOH)/微纤化纤维素(MFC)复合薄膜材料,以超临界二氧化碳(scCO₂)为物理发泡剂,采用间歇式降压法制备了一系列PVOH/MFC复合微发泡材料,主要讨论了在没有水分的影响下,不同发泡温度和时间以及MFC含量对PVOH/MFC复合微发泡材料的泡孔形貌、泡孔尺寸和泡孔密度的影响;同时,也对MFC的分散性和PVOH/MFC复合材料的流变性能和热性能对发泡行为的影响进行了研究。实验结果表明,均匀分散在PVOH基体中的MFC作为异相成核剂提高了气孔成核能力,且随着MFC含量的增加,泡孔尺寸降低,泡孔密度增大;并研究了发泡温度对PVOH/MFC复合材料的发泡形貌的影响,获得最优发泡温度。     

Gellan/poly(vinyl alcohol) hydrogels: characterization and evaluation as delivery systems

Bioartificial polymeric materials in the form of hydrogels were prepared starting from blends of poly(vinyl alcohol) (PVOH) with gellan, using a procedure based on freeze–thawing cycles. The effect exerted by gellan on the properties of these materials was investigated. The materials were loaded with human growth hormone (GH) and the release of the drug was evaluated. The results obtained indicated that gellan favours the crystallization process of PVOH allowing the formation of a material with a more homogeneous and stable structure than that of pure PVOH hydrogels. Both the PVOH melting enthalpy and the elastic modulus increased with increasing gellan content in the hydrogels; in addition, the higher the gellan content in the samples, the lower was the amount of PVOH released. Gellan/PVOH hydrogels were able to release GH and the release was affected by the content of the biological component. The amount of GH released was within a physiological range. © 2001 Society of Chemical Industry     

Synthesis,characterization, and properties of poly(vinyl acetate)‐ and poly(vinyl alcohol)‐grafted chitosan

Graft copolymers of chitosan and vinyl acetate were synthesized by free radical technique using cerium (IV) as the initiator. Under controlled conditions, as much as 92% grafting with a grafting yield of 30–40% could be achieved. Chitosan‐g‐poly(vinyl alcohol) copolymers were derived by the alkaline hydrolysis of the chitosan‐g‐poly(vinyl acetate) precursor. Thermogravimetric, FTIR, and X‐ray diffraction analyses of chitosan and the copolymers confirmed the grafting reaction between chitosan and vinyl acetate and also the subsequent hydrolysis. Both the copolymers possessed very good film‐forming properties. Grafting resulted in a significant increase in mechanical strength of both the copolymers in the dry condition. Chitosan‐g‐poly(vinyl acetate) (CH‐PVAc) proved more hydrophobic than did pure chitosan, whereas chitosan‐g‐poly(vinyl alcohol) (CH‐PVOH) exhibited enhanced hydrophilicity as evident from their swelling characteristics and contact angle measurements. The enhanced swelling of CH‐PVOH was ascribed to the presence of the pendant poly(vinyl alcohol) group. At pH 1.98, the CH‐PVAc copolymer films showed greater stability than do pure chitosan films, which is highly beneficial for specific biomedical applications. Both the copolymers showed lower glass transition temperature than do pure chitosan. Grafting did not affect the overall thermal stability, and the differential thermogram substantiated the grafting. The investigations indicate that the synthetic–natural hybrid copolymers having desirable mechanical properties and tailored hydrophilic/hydrophobic characteristics are realizable. These polymers could be exploited for varied biomedical applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1852–1859, 2007     

Effect of citric acid,PVOH, and starch ratio on the properties of cross-linked poly(vinyl alcohol)/starch adhesives

The properties of tapioca starch adhesives were improved by cross-linking and the cross-linked adhesive compared with pure tapioca starch and poly(vinyl alcohol) adhesives. The effect of starch ratio, type of PVOH, and adding citric acid were important factors on the cross-linked adhesives. Wood adhesives made from cross-linked PVOH/starch were prepared by PVOH and tapioca starch, using hexamethoxymethyl melamine (HMMM) and citric acid (CA) as a cross-linking agent and catalyst, respectively. The effect of CA, PVOH/starch ratio, and type of PVOH such as medium (M PVOH) and high molecular weight (H PVOH) were investigated. The condition of the cross-linking reaction was 175?°C for 15?min. The structural properties of cross-linked adhesive were investigated by FT-IR spectroscopy. The results were confirmed in terms of thermal properties with a differential scanning calorimeter (DSC) and the shear strength of the adhesive. The cross-linked adhesive resulted in the increase of T _g and showed good blend compatibility with all of the cross-linked adhesives. The adhesive strength significantly increased when using CA as a catalyst in the cross-linking reaction. The optimum contents of the cross-linked PVOH/starch adhesives were 1:1.8 for M PVOH and 1:0.5 for H PVOH.     

An NMR study of the dissociation of N,N′-(2-propyloximino)-4,4′-methylenebis(phenylcarbamate) and its crosslinking of polymers containing labile hydrogens. II

Nuclear magnetic resonance spectroscopy has been used to study the dissociation and reaction of N,N′-(2-propyloximino)-4,4′-methylenebis(phenylcarbamate), as a crosslinking agent for polymers containing labile hydrogens. The crosslinking of poly(acrylic acid), polyacrylamide, and poly(vinyl alcohol) was found to result upon heating each to 150°C for 10 min with this component at 2–10 wt %.     

Incorporation of high oil content in polyvinyl acetate nanoparticles produced by batch miniemulsion polymerization stabilized with a polymeric stabilizer

Nanoparticles (NPs) have been widely applied in the biomedical area. In order to satisfy the requirements for biomedical applications, sodium lauril sulfate (SLS) and hexadecane, widely used as anionic surfactant and co‐stabilizer, were successfully replaced by biocompatible compounds, in order to obtain poly(vinyl acetate) (PVAc) NPs via miniemulsion polymerization. The incorporation of high oil content in PVAc NPs was investigated, using different poly(vinyl alcohol) (PVOH) concentrations as polymeric surfactant. Besides the polymeric surfactant, lecithin and Miglyol 812, a triacylglycerol of saturated fatty acids obtained from coconut oil, were used as surfactant and co‐stabilizer, respectively. A high Miglyol 812 content was incorporated in the PVAc NPs and the morphology was investigated by TEM. The influence of PVOH concentration on the droplet nucleation mechanism and final morphology of PVAc NPs was evaluated. High PVOH concentration favored micellar particle nucleation. According to the TEM images, hemispheres nanoparticles were obtained. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41365.     

Physical and mechanical properties of plasticized butenediol vinyl alcohol copolymer/thermoplastic starch blend

The poly(vinyl alcohol) (PVOH) is an eco‐friend polymer and has an excellent oxygen barrier property due to its strong intermolecular force, but difficulty in processing with conventional extrusion process gives it a limitation for various industrial applications, especially packaging industry. Many studies have attempted to plasticize PVOH to improve its processability, but high cost of PVOH is still drawback for a variety of industrial applications. Therefore, PVOH often blended with other biodegradable polymers such as starch to acquire the cost benefit. Nowadays, the butenediol vinyl alcohol copolymer (BVOH) is getting a great attention due to its melt processability and bio‐degradability, but its high cost is barrier to the industrial application as well. In this study, thermoplastic starch (TPS)/plasticized BVOH (P‐BVOH) were prepared by melt mixing technique, and the plasticization effect of glycerol on starch and BVOH with different composition was observed for optimized processing condition. Based on our preliminary study, TPS was blended with varying amount of P‐BVOH (100:0, 90:10, 80:20, 70:30, 60:40, and 50:50 weight ratio). Physical, oxygen barrier, and mechanical properties of the TPS/P‐BVOH blends were evaluated by various analytical instruments to achieve balanced property and performance. J. VINYL ADDIT. TECHNOL., 25:109–116, 2019. © 2018 Society of Plastics Engineers     

Effect of mechanical treatments on orientation behavior and spectral properties of azoderivative dyes incorporated in poly(vinyl alcohol) films

Various azoderivative dyes were incorporated in uncolored poly(vinyl alcohol) (PVOH). One type of film was obtained by drying the layer of solution cast on glass plate. The other type was obtained by rubbing the PVOH layer before complete drying. Linear birefringence and dichroism of dyed polymer films were investigated as a function of stretching degree. An increase in the linear birefringence was found with increasing stretching degree for both uncolored and colored films. Dichroism of the PVOH films depends on the dye chemical structure and also on the stretching degree of both non-rubbed and rubbed and dyed PVOH samples. Molecular modeling was used to examine interactions occurring between PVOH and the embedded dye molecule. These stretching degree dependencies were approximated mathematically, which was used to describe the behavior of some components of interference filters.     

Effects of jackfruit waste flour on the properties of poly(vinyl alcohol) film

A series of biodegradable polymer films based on poly(vinyl alcohol) (PVOH) and jackfruit waste flour (JWF) was prepared in the presence of water and glycerol and cast by a solution casting method. The JWF was introduced as a promoter of biodegradability. The blended films were evaluated for their tensile properties, water absorption, water vapor transmission rate (WVTR), and degradation behavior under different environmental conditions such as natural weathering and natural soil. The tensile strength (1.7–6.4 MPa) and elongation at break (13–108%) of the PVOH/JWF films were lower than those of unfilled PVOH film (26MPa and 238%). However, the Young's modulus values (157–196 MPa) of the PVOH/JWF films were higher than that of unfilled PVOH film (137 MPa). The PVOH/JWF blended films showed higher water absorption and WVTR, which increased with increasing JWF content. Biodegradability tests revealed that the presence of JWF stimulated the degradation rate and caused the weight loss and reduction in tensile properties of the PVOH/JWF blended films. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Immobilization of bacteriocin nisin into a poly(vinyl alcohol) polymer matrix crosslinked with nontoxic dicarboxylic acid

This work is focused on novel methodology of poly(vinyl alcohol) crosslinking by non‐toxic dicarboxylic acid, glutaric acid. The cross‐linked system was used as a matrix for immobilization of bacteriocin nisin. Effect of the crosslinking degree on physico‐chemical, morphology, mechanical, and thermal properties of poly(vinyl alcohol) films were investigated by using swelling test, Fourier transform infrared spectroscopy, scanning electron microscopy, stress–strain analysis, differential scanning calorimetry, and thermogravimetry. Release profile of the nisin from the cross‐linked poly(vinyl alcohol) was studied by high performance liquid chromatography. Antibacterial activity of the prepared systems was tested by agar diffusion test and dilution and spread plate technique. Results showed suitability of glutaric acid as effective crosslinking agent of poly(vinyl alcohol) that acts synergistically with bacteriocin nisin against the tested Gram‐positive and Gram‐negative bacterial strains. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43674.     

Influence of the nanofiber dimensions on the properties of nanocellulose/poly(vinyl alcohol) aerogels

The investigation of aerogels made from cellulose nanofibers and poly(vinyl alcohol) (PVOH) as a polymeric binder is reported. Aerogels based on different nanocellulose types were studied to investigate the influence of the nanocellulose dimensions and their rigidity on the morphology and mechanical properties of the resulting aerogels. Thus, cellulose nanocrystals (CNCs) with low (10), medium (25), and high (80) aspect ratios, isolated from cotton, banana plants, and tunicates, respectively, microfibrillated cellulose (MFC) and microcrystalline cellulose (MCC) were dispersed in aqueous PVOH solutions and aerogels were prepared by freeze‐drying. In addition to the cellulose type, the PVOH‐ and the CNC‐concentration as well as the freeze‐drying conditions were varied, and the materials were optionally cross‐linked by an annealing step or the use of a chemical cross‐linker. The data reveal that at low PVOH content, rigid, high‐aspect ratio CNCs isolated from tunicates afford aerogels that show the least amount of shrinking upon freeze‐drying and display the best mechanical properties. However, with increasing concentration of PVOH or upon introduction of a chemical cross‐linker the differences between materials made from different nanocellulose types decrease. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41740.     

疏水改性聚乙烯醇的黏度行为

以２,４ 二异氰酸甲苯酯作交联剂将十四醇、十八醇作为疏水基引入聚乙烯醇分子中,合成疏水性缔合型增稠剂。当疏水基的摩尔分数仅为０．２５ ％ 时,聚乙烯醇水溶液的黏度就会迅速增高,且水溶液的耐盐能力大大增加。以摩尔分数为０．２５％ 的十八醇疏水基改性聚乙烯醇后,在ｗ（ＮａＣｌ）＝ ６％ 溶液中仍保持黏度的稳定性。     

Self-healing quadruple shape memory hydrogels based on coordination,borate bonds and temperature with tunable mechanical properties

Quadruple shape memory hydrogels were prepared by one-pot in situ copolymerization using acrylamide, acrylic acid, agar, and poly(vinyl alcohol). The hydrogels have multiple reversible shape memory based on the coordination bonds of poly(acrylic acid) with Fe3+, borate bonds based on poly(vinyl alcohol), and hydrogen bonds of agar and poly(vinyl alcohol). The hydrogel demonstrated tunable mechanical properties when the hydrogels immersed in different solutions for various lengths of time. After immersion in the ferric chloride solution, tensile stress and elastic moduli of the hydrogels were enhanced with increasing soaking time. After immersion in the borax solution, tensile stress first increased and then decreased with increasing soaking time. Due to the reversible effect of the borate bond, the hydrogel achieved ultra-fast self-healing. The hydrogel after immersion in borax solution could begin healing in 24 h and healed at 44 h. The tensile stress and tensile strain of the self-healing hydrogel increased when soaking time increased from 48 to 96 h, and tensile stress at healing times of 96 h was nearly as the same as that of the original hydrogel when compared with it. The combination of tunable mechanical properties, efficient recoverability and self-healing abilities coupled with facile preparation endowed the developed hydrogel a high potential for use in biomedical applications.     

Properties of the crosslinked plasticized biodegradable poly(vinyl alcohol)/rambutan skin waste flour blends

Poly(vinyl alcohol) (PVOH)/rambutan skin waste flour (RWF) crosslinked films were successfully prepared by solution casting with glutaraldehyde (GLU) and hexamethylenetetramine (HMTA) and without crosslinker in the presence of glycerol as a plasticizer. The properties of cast films were evaluated by tensile testing, water absorption, and degradation behavior at different weight ratios of PVOH and RWF. The tensile results show that the PVOH/RWF films crosslinked with HMTA exhibited a slight improvement in the tensile strength and Young's modulus but a lower elongation at break than that of GLU-crosslinked films; this was attributed to the better crosslinking effect of HMTA, as shown by the Fourier transform infrared results. The HMTA-crosslinked film showed a lower water absorption and water vapor transmission rate as compared to the GLU-crosslinked and noncrosslinked films. A natural weathering test revealed that the addition of 1.5 wt % GLU and HMTA did not significantly affect the reduction in tensile properties, but the biodegradability test showed that the weight loss of noncrosslinked films was higher than those of the GLU- and HMTA-crosslinked films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Separation of MTBE-Methanol Mixtures by Pervaporation

Abstract

Membranes made of a polymer blend of poly(acrylic acid) and poly(vinyl alcohol) were evaluated for the separation of methanol from methyl tert-butyl ether (MTBE) by pervaporation. The influence of the blend composition and the feed composition on the pervaporation performance were investigated. Methanol permeates preferentially through all tested blend membranes, and the selectivity increases with increasing poly(vinyl alcohol) content in the blends. However, a flux decrease is observed with increasing poly(vinyl alcohol) content. With increasing feed temperature the flux increases, and the selectivity remains constant. In addition, the influence of crosslinking on the permselectivity was investigated. The pervaporation flux decreases with increasing crosslinking density, but the selectivity is enhanced. This is due to a more rapid decrease in the component flux of MTBE compared to that of methanol.     

New Types of Ecologically Safe Flame Retardant Polymer Systems

Abstract

New types of ecologically safe flame retardant composition based on poly(vinyl)alcohol and poly(vinyl)alcohol oxidized by KMnO₄ (polymer-organic char formers) were proposed for nylon 6,6. These systems can promote the formation of char by intermolecular crosslinking (“synergetic carbonization”). The Cone Calorimeter tests indicated the improvement of fire retardant properties for the compositions of nylon 6,6 with poly(vinyl)alcohol and poly(vinyl)alcohol oxidized by KMnO₄ in comparison with pure nylon 6,6.