Increasing PVA Content Research Articles

Amphibious hybrid nanostructured proton exchange membranes

▶ PVA enhances the film-forming capacity at a high acid doping level. ▶ PVA does not influence the thermal stability obviously. ▶ Increasing PVA content leads to a matrix change between PVA and PGA. ▶ PVA facilitates the proton conduction of the soaked membrane under wet conditions. Amphibious proton exchange membranes (PEMs) which could be used under both wet and dry conditions were prepared by sol–gel method in this work. Those novel hybrid PEMs were constructed by three parts: (1) polysiloxane with two basic sites (–NH– on the pendant and N– in the triazole); (2) H 3 PO 4 as the proton source; (3) poly(vinyl alcohol) (PVA) which had good film-forming capacity and ability to anchor the H 3 PO 4 under wet conditions. The resulting hybrid membranes were thermally stabilized up to 200 °C. A matrix-change between polysiloxane and PVA could be observed at a high PVA doping level. The proton conducting property of these membranes was investigated under both hydrous and anhydrous conditions. From 25 to 120 °C, the non-soaked and soaked (soaked in the water) membranes showed the proton conductivity of 19–68 and 9–31 mS cm −1 at 100% relative humidity (RH), respectively. Under completely dry conditions, the proton conductivity of these membranes showed large dependence on the temperature and the proton conductivity of 4.7–21 mS cm −1 was achieved at 150 °C for these membranes. The excellent performance of these hybrid membranes under both wet and dry conditions demonstrated that they have potential use as electrolytes in polymer electrolyte membrane fuel cells (PEMFCs) operating either in a watery or in a water-free environment and so called “amphibious” proton conducting membranes.

Nylon 6 crystal‐phase transition in nylon 6/clay/poly(vinyl alcohol) nanocomposites

AbstractA study of the dependence of the poly(vinyl alcohol) (PVA) content on the nylon 6 crystal‐phase transition properties and PVA morphologies of nylon 6/clay nanocomposite (NYC)/PVA specimens was conducted. The degree of compatibility between NYC and PVA was examined by dynamic mechanical analysis measurement. The strong hydrogen bonding between the nylon 6 and PVA molecules led to nearly complete inhibition of PVA crystallization when the PVA contents were less than 16.7 wt %. Moreover, scanning electron microscopy analysis indicated that the clays originally present in the nylon 6 matrices migrated gradually into the PVA phases with increasing PVA content in the NYC/PVA series specimens. This interesting migration of clay from nylon 6 to PVA led to a nylon 6 crystal‐phase transition from the γ to the α form. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Thermal and optical properties of gelatin/poly(vinyl alcohol) blends

AbstractDifferential scanning calorimetry, thermogravimetric analysis, X‐ray diffraction, and ultraviolet–visible spectroscopy of gelatin and poly(vinyl alcohol) (PVA) homopolymers and their blended samples were studied. The data revealed that the gelatin and PVA polymers were compatible over the investigated range of compositions; this contributed to the formation of hydrogen‐bonding interaction between their polar groups. The associated enthalpy‐of‐melting transition and thermal stability of the blended samples increased with increasing PVA content. This indicated that the crystalline structure of PVA was not destroyed completely in the blends, which was consistent with the X‐ray diffraction pattern of the 50/50 (wt %/wt %) blended gelatin/PVA sample. The absorption edge and optical band gap for allowed direct transition were determined from ultraviolet–visible spectra. The induced changes in the band structure are elucidated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Moisture sorption and water vapor permeability of soy protein isolate/poly(vinyl alcohol)/glycerol blend films

The aim of the present work was to investigate the moisture sensitivity of films of soy protein isolate (SPI) blended with poly(vinyl alcohol) (PVA) and plasticized with glycerol. Water vapor permeability (WVP) and moisture sorption were measured based on the PVA and glycerol content of the films. WVP values of SPI/PVA films with and without glycerol were in the range 8.25–10.9 g mm (m 2 h kPa) −1, and were significantly affected by both PVA and glycerol. WVP values decreased with increasing PVA content. XRD analysis confirmed that the glycerol can enter the macromolecular blend structure and destroy the crystallinity of the blends. Crosslinking between glycerol molecules and SPI reduced the interstitial spaces in the protein matrix, thus decreasing the rate of diffusion of water molecules through the films. Moisture adsorption and sorption isotherm data of SPI/PVA/glycerol were mathematically fitted to the GAB model. With increasing PVA content, the equilibrium moisture content (EMC) of film samples clearly decreased. That trend indicates that the addition of PVA decreased the ability of SPI protein molecules to absorb and accept water. EMC data and contact angle measurements showed that the addition of plasticizer not only loosened the microstructure of blended films, but also increased the hydrophilicity by exposing their hydroxyl groups.

Study on superabsorbent of maleic anhydride/acrylamide semi-interpenetrated with poly(vinyl alcohol)

A series of superabsorbents of maleic anhydride (MAH)/acrylamide (AM) interpenetrated with poly(vinyl alcohol) (PVA) were prepared by aqueous polymerization, using N,N-methylenebiacrylamide (NNMBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The samples were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscope (SEM). The effects of reaction variables on the water absorbency of the superabsorbents in distilled water and in 0.9 wt% NaCl solution were investigated. In addition, the effect of the PVA content on the swelling rate and sensitivity to saline of the superabsorbents were also investigated. The results showed that the absorbency, both in 0.9 wt% NaCl solution and in distilled water, first decreased and then increased with increasing PVA content. Moreover, the resultant superabsorbent had a higher absorption rate and it became less sensitive to saline by incorporating certain amount of PVA into the network of the hydrogel. Copyright © 2009 John Wiley & Sons, Ltd.

Preliminary study of SPEEK/PVA blend membranes for DMFC applications

The blend membranes consisting of PVA and SPEEK were investigated for the purpose of maintaining low methanol permeability and little swelling ratio in direct methanol fuel cells (DMFCs). SPEEK with different sulfonation degree were prepared by sulfonation of PEEK. Blend membranes with various PVA content were prepared by solvent casting. Thermal stability, uptake behavior, methanol permeability, ionic exchange capacity (IEC) and proton conductivity of the blend membranes were determined as function of PVA content. The results of TGA show that the addition of PVA increases the weight loss of the membranes at the temperature ranging from 250 °C to 350 °C and shifts the weight loss onset temperature ( T oneset) to lower direction. The uptake of blend membranes in water increases with the increase of PVA content, while the absorption of blend membranes in methanol solution show a decrease upon the PVA content, which can minimize the swelling ratio of electrolyte membrane in DMFC applications. The slightly lower ionic exchange capacity (IEC) and proton conductivity of the blend membranes indicate some interaction between SPEEK and PVA molecules. The lower methanol permeability of the blend membranes suggests its potential applications in DMFC.

Development of films based on blends of Amaranthus cruentus flour and poly(vinyl alcohol)

The aim of this work was to develop biodegradable films based on blends of Amaranthus cruentus flour and poly(vinyl alcohol). Five different PVA types were tested. Blends with higher hydrolysis (HD) degree PVA were more resistant, showing greater tensile strength (TS) and puncture force (PF). However, the films with PVA with lower HD showed more flexibility, greater elongation at break (ELO) and greater puncture deformation (PD), with the exception of PVA 325. The latter was chosen due to it superior mechanical performance (TS = 10.2 MPa, ELO = 89.8%, PF = 9.4 N and PD = 16.3%). When films based on blends of amaranth flour and PVA 325 (10–50%) were evaluated, all mechanical properties were enhanced with increase in PVA 325 content. The solubility in water of the films made with PVA and amaranth flour decreased with increasing PVA content, reaching 44% of soluble matter for the 50% PVA film. The formation of hydrogen bonds between the blend components was confirmed by the FTIR spectra analysis.

Gelation and Swelling Behavior of Semi-Interpenetrating Polymer Network Hydrogels Based on Polyacrylamide and Poly(vinyl alcohol)

Novel semi-Interpenetrating Polymer Network (semi-IPN) hydrogels based on partially Hydrolyzed Polyacrylamide (HPAM) and Poly(Vinyl Alcohol) (PVA) were prepared by solution crosslinking using chromium triacetate. Effects of PVA content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels decreased with increasing PVA content. It was also found that increasing the PVA content increases the loss factor, indicating that the viscous properties of this gelling system increase more strongly than the elastic properties. The swelling ratio of the semi-IPN gels in tap water decreased as the concentration of the PVA increased. However, the semi-IPN gels showed lower salt sensitivity factor in synthetic oil reservoir water as compared with HPAM gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.

Dehydration of acetic acid by pervaporation using SPEK-C/PVA blend membranes

Sulfonated cardo polyetherketone (SPEK-C) and poly(vinyl alcohol) (PVA) blend membranes were prepared by solution casting method and used in pervaporation (PV) dehydration of acetic acid. The membranes were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle meter. The results show that thermal crosslinking occurred to the membrane under high temperature annealing. The effective d-spacing (inter-segmental spacing) decreased with PVA content decreasing. The hydrophilicity of the blend membrane increased with SPEK-C content increasing. Swelling and sorption experiments show that the swelling degree of the blend membrane increased, however both the sorption and diffusion selectivities decreased with increasing PVA content. The diffusion selectivity is higher than the sorption selectivity. This suggests that PV dehydration of acetic acid is dominated by the diffusion process. The pervaporation separation index (PSI) of the membrane increases with increasing PVA content and arrives at a maximum when the SPEK-C/PVA ratio is 3/2, then decreases with further addition of PVA. The membrane has an encouraging separation performance with a flux of 492 g m −2 h −1 and separation factor of 59.3 at 50 °C at the feed water content 10 wt%.

Preparation and characteristics of crosslinked sulfonated poly(phthalazinone ether sulfone ketone) with poly(vinyl alcohol) for proton exchange membrane

In order to further overcome the trade-off between high conductivity and good mechanical property of proton exchange membrane (PEM), direct covalent crosslinking of sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) and poly(vinyl alcohol) (PVA) was prepared through post-heating process. Polymer PVA has attractive advantages to be a crosslinker with SPPESK, since the crosslinking of SPPESK with PVA requires relatively lower crosslinking temperature and has much higher stability in water, compared with small molecule crosslinker of glycol and glycerol. The crosslinking is confirmed by solubility change and analysis of ion exchange capacity (IEC) and sulfur content ( C S) of uncrosslinked and crosslinked SPPESK with PVA (Un S-P and Cr S-P). Calculation of degree of crosslinking (DC) of sulfonic group shows that most –SO 3Hs of SPPESK are not involved in the crosslinking, which can maintain the ion exchange and proton transport function. ATR-FTIR spectra analysis manifests the PVA in Cr S-P are oxidized and dehydrated during the crosslinking process with SPPESK. Cr S-P membrane still has higher thermal stability, despite T d (252–273 °C) is less than that (306 °C) of pristine SPPESK. SEM images and XRD patterns show that the Cr S-P is a homogenous and amorphous material. Water uptake of Cr S-P membrane decreases with increasing PVA content, and Cr S-P membrane with lower PVA content (e.g. 15% and 20%) has high water uptake (111.1% and 98.0%) at 80 °C. All the swelling ratio values of Cr S-P (15–35% of PVA content) are at a lower level (≤36%) even at 80 °C. Some Cr S-P membranes (with lower PVA content) have much higher conductivity than that of stable pristine SPPESK, e.g. conductivity of S-P 85/15 reaches 2.00 × 10 −2 S cm −1 which is almost twice as that (1.03 × 10 −2 S cm −1) of SPPESK DS 81% membrane. All above properties of Cr S-P membrane (especially PVA content: 15–20%) indicate the kind of crosslinked sulfonated polymer with PVA is another alternative or prospective approach to prepare PEM.

Pervaporation performance and Transport phenomenon of PVA blend membranes for the separation of THF/water azeotropic mixtures

Dense polymer membranes were made by mixing aqueous solutions of hydrophilic polymers poly(vinyl alcohol) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the separation of Tetrahydrofuran (THF)/water azeotropic mixtures by pervaporation (PV). In order to gain a more detailed picture of the molecular transport phenomenon, we have performed sorption gravimetric experiments at 30 °C to compute diffusion, swelling, sorption and permeability coefficients of PVA/PEI membranes in the presence of THF and water. The membranes were found to have good potential for breaking the azeotrope of THF at 6% concentration of water. An increase in PVA content in the blend caused a reduction in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest separation factor of 181.5, exhibited a flux of 1.28 kg/m2h for THF respectively at azeotropic feed composition.

Synthesis of starch‐based plastic films by electron beam irradiation

AbstractStarch‐based plastic films were prepared by the electron beam irradiation of starch and poly(vinyl alcohol) (PVA) in a physical gel state at room temperature. The influence of starch/PVA composition, irradiation dose, and plasticizer (glycerol) on the properties of the plastic films was investigated. The gel fraction of the starch/PVA films increased with both the radiation dose and PVA content in the plastic film and decreased with increasing glycerol concentration. The starch/PVA compatibility was determined by measurement of the thermal properties of the starch/PVA blends with various compositions with differential scanning calorimetry. The swelling of the starch/PVA films increased with increasing PVA content and decreasing irradiation dose. Mechanical studies were carried out, and the tensile strength of the films decreased at high starch ratios in the starch‐based mixture. This was due to the decrease in the degree of crosslinking of starch. Furthermore, when PVA, a biodegradable and flexible‐chain polymer, was incorporated into the starch‐based films, the properties of the films, such as the flexibility (elongation at break), were obviously improved. The tensile strength of the films decreased with increasing glycerol concentration, but elongation at break increased up to a maximum value at a 20% glycerol concentration, and then, it leveled off and decreased slightly. Biodegradation of the starch/PVA plastic films was indicated by weight loss (%) after burial in soil and morphological shape, which was detected by scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 504–513, 2007

Swelling of pH‐sensitive chitosan–poly(vinyl alcohol) hydrogels

AbstractThe swelling properties of different chitosan–poly(vinyl alcohol) (PVA) hydrogels were investigated as functions of the medium pH and salt concentration. The maximum swelling ability of the hydrogels was at a buffer pH of approximately 3, regardless of the PVA content in the hydrogels. The maximum mass of the swollen hydrogels was about 13 times that of their contracted counterparts. The cyclical swelling and contraction between pH 3 and pH 7 buffers and pH 3 and pH 3 buffers with salt confirmed the Donnan swelling mechanism of these hydrogels. The swelling mechanism was considered the transfer of water molecules driven by a concentration gradient. This was represented by a simplified mass‐balance model, which neglected the effect of the ionization reaction, for the initial swelling period. The effective mass‐transfer coefficient of water molecules during swelling, estimated with this model, gradually decreased with increasing PVA content in the hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4665–4671, 2006

New Biodegradable Blends from Aliphatic Polycarbonate and Poly(vinyl alcohol)

Poly(propylene carbonate/poly(vinyl alcohol) (PPC/PVA) blends with various PVA contents were prepared by a solution casting technique. The thermal and mechanical properties and the morphologies of the blends were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), static mechanical measurements, scanning electron microscopy (SEM) and FT-IR techniques. The TGA results showed that the introduction of PVA led to a slightly earlier decomposition of the PPC. DSC analysis and SEM observation indicated that the PPC/10% PVA blend was a miscible system, while those containing more than 20% of PVA were two phase systems. FT-IR revealed that the hydroxyl-stretching peak shifted to a higher wave number, and the carbonyl-stretching peak to a lower wave number with increasing PVA content. This indicated a specific interaction between PVA and PPC. Therefore the tensile strength and stiffness of the blends tended to increase greatly with increasing PVA content.

Alginate–poly(vinyl alcohol) core–shell microspheres for lipase immobilization

AbstractA lipase [triacylglycerol ester hydrolase (EC 3.1.1.3)] was encapsulated in sodium alginate (AlgNa)/poly(vinyl alcohol) (PVA) microspheres. Spherical AlgNa/PVA beads were prepared by the ionotropic gelation of an AlgNa/PVA blend in the presence of calcium tetraborate (CaB4O7). The particles were spherical and had an average diameter of 400 μm. The microspheres were studied with differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, and water transport by the equilibrium degree of swelling. The elevation of the glass‐transition temperature of the microspheres indicated specific crosslinking reactions of the component polymers (AlgNa/PVA). FTIR spectra showed no evidence of a strong chemical interaction changing the nature of the functional groups of both AlgNa and PVA in the AlgNa/PVA blends. The water diffusion coefficients increased with increasing PVA content in the microspheres, indicating a decrease in the resistance to mass transfer through the AlgNa/PVA microsphere wall. The AlgNa/PVA microspheres were characterized by the Michaelis constant (KM) and the maximum reaction velocity (Vmax), which were determined for both free and immobilized lipases. The enzyme affinity for the substrate (KM/Vmax) remained quite good after immobilization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1553–1560, 2006

Effect of blending ratio on pervaporative separation of 1,4-dioxane/water mixtures through PVA–PEI membranes

Blend membranes were made by mixing aqueous solutions of hydrophilic polymers poly(vinyl alcohol) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the separation of 1,4-dioxane/water azeotropic mixture by pervaporation (PV). Water forms azeotrope at 18 wt% concentration with 1,4-dioxane. The resulting membranes were characterized by FTIR to verify the interaction between the homopolymers, wide-angle X-ray diffraction (WAXD) to observe the effect of blending on crystallinity and thermal gravimetric analysis (TGA) to investigate the thermal stability. Sorption studies were carried out to evaluate the extent of interaction and degree of swelling of the blend membranes in pure liquids as well as binary mixtures. The effect of blend composition ratio on membrane parameters such as flux and selectivity was analyzed. An increase in PVA content in the blend caused a reduction in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest separation factor of 44.01 and exhibited a flux of 0.733 kg/m 2 h 10 μm for azeotropic feed composition at ambient temperature (30 °C).

Properties of fish protein–hydrophilic polymer hybrid gels

Biogels and bio-hybrid gels were prepared from myofibril of fish and their properties were evaluated. The muscular protein used was extracted from fish meat. After washing and centrifugal separation, the muscular protein was mixed with 3 wt % of NaCl and the gels were prepared by heating the mixtures from 50 to 90 °C. The bio-hybrid gels were prepared from fish protein gel and poly(vinyl alcohol). Tensile tests revealed that the tensile strength, strain at break and Young’s modulus of heated hybrid gels prepared at 50, 80 and 90 °C increased with increasing preparation temperature. This can be explained by the difference in crosslinking density. Also, the heated gels showed a good response to electric field in acid and alkaline solutions. Young modulus, tensile strength and elongation at break of the bio-hybrid gels increased with an increasing PVA content. Bending of hybrid gels in solutions of various pH under the electric stimulus was observed. The largest bending angle was 20–30 °C at pH=1.2.

Molecular Origins of Wettability of Hydrophobic Poly(vinylidene fluoride) Microporous Membranes on Poly(vinyl alcohol) Adsorption: Surface and Interface Analysis by XPS

Irreversible adsorption of poly(vinyl alcohol) (PVA) on hydrophobic, porous poly(vinylidene fluoride) (PVDF) membranes was carried out using aqueous PVA solution. Water permeation was observed in PVDF microporous membranes after PVA adsorption, and maximum permeability was obtained after treatment with 4% PVA solution. Water permeability increased linearly with increasing PVA concentration up to 4%, and then a marginal decrease with a further increase in PVA concentration occurred. PVA adsorbed PVDF membranes were subjected to intense physicochemical analysis, especially with XPS. XPS results display the presence of an interface between PVA and PVDF, and the binding energy (BE) of the interface is low for the PVDF membranes treated with 4% PVA. Carbon from CF2-groups and F 1s core level clearly showed a decrease in its content on the surface after PVA adsorption and showed a minimum fluorine content at 4% PVA. F 1s BE shifts by 0.5 eV upon PVA adsorption and is independent of PVA concentration. EDAX analysis indicates that the bulk oxygen content remains within 4.5 +/- 0.6% and is independent of the PVA concentration. Nonetheless, a large amount of surface atom percentage of oxygen (20 +/- 4%) from O 1s core level shows an increase in PVA content on the surface of PVDF, and it is restricted mostly to the surface. The 4% PVA treated PVDF membrane clearly shows a broadening of O 1s core level to lower BE and indicates the interaction between PVDF and PVA which is significantly different compared to any other compositions. A new valence band feature at low BE, which is nonexistent on PVDF, develops after PVA adsorption. This indicates that the shift in the nature of the highest occupied molecular orbital (HOMO) derived mostly from oxygen; simultaneously, a suppression in the PVDF derived band indicates the change in nature of the PVA adsorbed surfaces from hydrophobic to hydrophilic. The above observations also suggest an irreversible electronic interaction between PVA and PVDF, possibly through charge transfer.

Different viscosity grade sodium alginate and modified sodium alginate membranes in pervaporation separation of water + acetic acid and water + isopropanol mixtures

Different viscosity grade sodium alginate (NaAlg) membranes and modified sodium alginate membranes prepared by solution casting method and crosslinked with glutaraldehyde in methanol:water (75:25) mixture were used in pervaporation (PV) separation of water+acetic acid (HAc) and water+isopropanol mixtures at 30 °C for feed mixtures containing 10–50 mass% of water. Equilibrium swelling experiments were performed at 30 °C in order to study the stability of membrane in the fluid environment. Membranes prepared from low viscosity grade sodium alginate showed the highest separation selectivity of 15.7 for 10 mass% of water in the feed mixture, whereas membranes prepared with high viscosity grade sodium alginate exhibited a selectivity of 14.4 with a slightly higher flux than that observed for the low viscosity grade sodium alginate membrane. In an effort to increase the PV performance, low viscosity grade sodium alginate was modified by adding 10 mass% of polyethylene glycol (PEG) with varying amounts of poly(vinyl alcohol) (PVA) from 5 to 20 mass%. The modified membranes containing 10 mass% PEG and 5 mass% PVA showed an increase in selectivity up to 40.3 with almost no change in flux. By increasing the amount of PVA from 10 to 20 mass% and keeping 10 mass% of PEG, separation selectivity decreased systematically, but flux increased with increasing PVA content. The modified sodium alginate membrane with 5% PVA was further studied for the PV separation of water+isopropanol mixture for which highest selectivity of 3591 was observed. Temperature effect on pervaporation separation was studied for all the membranes; with increasing temperature, flux increased while selectivity decreased. Calculated Arrhenius parameters for permeation and diffusion processes varied depending upon the nature of the membrane.

Polarized Optical Microscopy of Cellulose/Poly(vinyl alcohol) Blend Gel Fibers.

Cellulose/poly (vinyl alcohol) (PVA) blend gel fibers were prepared by extrusion of the blend solutions in N, N-dimethylacetamide-LiCl from tubular flow field into methanol. Influences of PVA content and flow on the macroscopic orientation of cellulose in the gel fibers were examined by polarized optical microcscopy. Cellulose chains had a strong tendency to orient parallel to the gel wall. The degree of the chain orientation was much lowered with increasing PVA content. Under the lowest flow rate, with increasing PVA content, the orientational distribution deviated from longitudinal to circumferential direction. These results were attributed to influences of the interactions between the two polymers. Under the higher flow rate, all the resultant gels exhibited the larger die swell with the latter type of orientational deviation. From the observation of a PVA gel phase which remained after the treatment with the enzyme, most of PVA chains were deduced to exist as amorphous chains in the blend gel fibers.