Synthesis and characterization of polyacrylamide‐grafted sodium alginate copolymeric membranes and their use in pervaporation separation of water and tetrahydrofuran mixtures

Polyacrylamide‐grafted sodium alginate (PAAm‐g‐Na‐Alg) copolymeric membranes have been prepared, characterized, and used in the pervaporation separation of 10–80 mass % water‐containing tetrahydrofuran mixtures. Totally three membranes were prepared: (1) neat Na‐Alg with 10 mass % of polyethylene glycol (PEG) and 5 mass % of polyvinyl alcohol (PVA), (2) 46 % grafted PAAm‐g‐Na‐Alg membrane containing 10 mass % of PEG and 5 mass % of PVA, and (3) 93 % grafted PAAm‐g‐Na‐Alg membrane containing 10 mass % of PEG and 5 mass % of PVA. Using the transport data, important parameters like permeation flux, selectivity, pervaporation separation index, swelling index, and diffusion coefficient have been calculated at 30°C. Diffusion coefficients were also calculated from sorption gravimetric data of water–tetrahydrofuran mixtures using Fick's equation. Arrhenius activation parameters for the transport processes were calculated for 10 mass % of water in the feed mixture using flux and diffusion data obtained at 30, 35, and 40°C. The separation selectivity of the membranes ranged between 216 and 591. The highest permeation flux of 0.677 kg/m² h was observed for 93% grafted membrane at 80 mass % of water in the feed mixture. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 272–281, 2002     

Pervaporation separation of water/dimethylformamide mixtures using poly(vinyl alcohol)‐g‐polyacrylamide copolymeric membranes

Grafted copolymeric membranes of poly(vinyl alcohol) with acrylamide (PVA‐g‐AAm) were developed and used in the pervaporation separation of water–dimethylformamide mixtures by varying the amount of water in the feed from 0 to 100%. From these data, the permeation flux, pervaporation separation index, diffusion coefficient, swelling index, and separation selectivity were calculated at 25, 35, and 45°C. The Arrhenius activation parameters for permeation flux ranged between 22 and 63 kJ/mol, while the activation energy for diffusion ranged between 23 and 67 kJ/mol. Separation selectivity was between 15 and 22. The highest permeation flux of 0.459 kg m^?2 h^?1 was obtained for the 93% grafted membrane at 90% of water in the feed mixture. The results are discussed using the principles of the solution–diffusion model. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 273–282, 2002     

Sorption,diffusion, and pervaporation separation of water–acetic acid mixtures through the blend membranes of sodium alginate and guar gum‐grafted‐polyacrylamide

Nonporous homogeneous dense membranes were prepared from the blends of sodium alginate (Na–Alg) with guar gum‐grafted polyacrylamide (GG‐g‐PAAm) in the ratios of 3 : 1 and 1 : 1 and these were tested for the pervaporation separation of water–acetic acid mixtures at 30°C. Blend compatibility was studied in solution by measuring the viscosity and the speed of sound. Membranes were crosslinked by glutaraldehyde. The GG‐g‐PAAm polymer and the crosslinked blend membranes were characterized by Fourier transform infrared spectra. High separation selectivity was exhibited by the pure Na–Alg membrane for water–acetic acid (HAc) mixtures containing 20 mass % of water. The permeation flux increased with increasing mass percent of water in the feed as well as with an increase in the amount of GG‐g‐PAAm in the blend, but separation selectivity decreased. Sorption selectivity was higher for the Na–Alg membrane than for the blend membranes, but it decreased with increasing mass percent of GG‐g‐PAAm in the blends. Diffusion selectivity values vary systematically with the blend composition, but not with the amount of water in the feed. Diffusion coefficients of the water–HAc mixtures were calculated from Fick's equation using sorption data and compared with those calculated from flux values obtained in pervaporation experiments. The Arrhenius activation parameters were calculated for the 20 mass % of water in the feed using flux and diffusion data obtained at 30, 40, and 50°C. The diffusion and pervaporation results are explained in terms of solution–diffusion concepts. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 259–272, 2002     

Synthesis of graft copolymeric membranes of poly(vinyl alcohol) and polyacrylamide for the pervaporation separation of water/acetic acid mixtures

Graft copolymers of poly(vinyl alcohol) (PVA) with polyacrylamide were prepared and membranes were fabricated at 48 and 93% grafting of acrylamide onto PVA. These membranes were used in the pervaporation separation of water/acetic acid mixtures at 25, 35, and 45°C. The permeation flux, separation selectivity, diffusion coefficient, and permeate concentration were determined. The highest separation selectivity of 23 for neat PVA at 25°C and the lowest value of 2.2 for 93% acrylamide‐grafted PVA membranes were observed. A permeation flux of 1.94 kg m^?2 h^?1 was found for the 93% grafted membrane at 90 mass % of water in the feed mixture. The diffusion coefficients in a water/acetic acid mixture had an effect on the membrane permselectivity. The Arrhenius equation was used to calculate the activation parameters for permeation as well as for the diffusion of water and of acetic acid. The activation energy values for the permeation flux varied from 97 to 28 kJ/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 244–258, 2002     

Pervaporation separation of water‐isopropyl alcohol mixtures with blend membranes of sodium alginate and poly(acrylamide)‐grafted guar gum

The blend membranes of sodium alginate (Na‐Alg) and poly(acrylamide)‐grafted guar gum (PAAm‐g‐GG) in the ratios of 3:1 and 1:1 were prepared and studied for the pervaporation separation of water–isopropyl alcohol mixtures over the entire range of mixture composition at 30°C. Membranes prepared from neat Na‐Alg (M‐1) and the 1:1 blend of Na‐Alg and PAAm‐g‐GG (M‐3) showed the highest separation selectivity for 10 mass % water in the feed mixture, whereas membranes prepared with the 3:1 blend ratio of Na‐Alg to PAAm‐g‐GG showed the highest separation selectivity of 20 mass % water in the feed. Selectivity decreased with increasing amount of water in the feed for all the membranes, but these values show an increase with increasing amount of grafted copolymer in the blend mixture. Flux increased with increasing amount of water in the mixture, but the flux values did not change markedly with the PAAm‐g‐GG content in the blend membrane at the lower mass % water. At higher mass % of water, the flux values of the blends increase systematically with increasing amount of PAAm‐g‐GG in the blend polymer. For the 10 mass %‐containing binary mixtures, the pervaporation separation experiments were performed at 30, 40, and 50°C, and the resulting data were used to calculate the Arrhenius activation parameters. These data indicated activated pore‐type diffusion of the permeants in the membranes. Dynamic sorption studies were also performed on up to 40 mass % water–isopropyl alcohol mixtures at 30°C. These results, when analyzed by the empirical equation, indicated Fickian transport in all the cases. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2014–2024, 2002     

Synthesis and characterization of polyacrylamidegrafted sodium alginate membranes for pervaporation separation of water + isopropanol mixtures

Polyacrylamide‐grafted‐sodium alginate copolymers were prepared by persulfate‐induced radical polymerization by using polymer‐to‐monomer ratios of 2 : 1 and 1 : 1. Polymers were characterized by Fourier transform infrared spectroscopy, differential thermal analysis, and viscosity. Membranes were prepared from the polymers, crosslinked with glutaraldehyde, and used in the pervaporation separation of water + isopropanol mixtures at 30°C. Equilibrium swelling experiments were performed for mixtures containing 10 to 80 mass % of water in the feed. Both the grafted copolymer membranes were ruptured while separating 10 mass % of water in the feed mixture. However, beyond 20 mass % of water in the feed mixture, flux increased with increasing grafting ratio, while selectivity decreased. Pervaporation separation experiments were carried out at 30, 40, and 50°C for 20 mass % of water in the feed mixture. By increasing the temperature, flux increased, whereas selectivity decreased. Arrhenius activation parameters for pervaporation and diffusion decreased with increasing grafting ratio of the membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2030–2037, 2004     

Comparison of the pervaporation separation of a water–acetonitrile mixture with zeolite‐filled sodium alginate and poly(vinyl alcohol)–polyaniline semi‐interpenetrating polymer network membranes

The pervaporation (PV) separation performance of ZSM‐5‐ and Na‐Y‐type zeolite‐filled sodium alginate (NaAlg) membranes were compared with those of pure NaAlg and semi‐interpenetrating polymer network (semi‐IPN) membranes of poly(vinyl alcohol) (PVA) with polyaniline (PANI) for the dehydration of acetonitrile. The PV separation characteristics of the zeolite‐filled membranes showed a dependence on the nature of the zeolites. The variation of the acidity function of the ZSM‐5 zeolite had an influence on the flux and selectivity of the membranes when compared to unfilled membranes. The crosslinked membranes were characterized by differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. Increasing the PANI content of the semi‐IPN network increased the separation selectivity. Among the NaAlg membranes, the plain NaAlg membrane showed the highest selectivity of 414 at 30 mass % water in the feed mixture, whereas the Na‐Y‐ and ZSM‐5 (40)‐filled NaAlg membranes exhibited much lower values of selectivity, that is, 7.3 and 4.3, respectively for 30 mass % water in the feed. When the flux and selectivity data of ZSM‐5 (250)‐filled NaAlg membranes were compared with that of Na‐Y‐ or ZSM‐5 (40)‐filled NaAlg membranes, a noticeable increase in the selectivity for the ZSM‐5 (250)‐filled NaAlg membrane was observed, but a somewhat comparable flux was observed compared to the plain NaAlg membrane. For the first time, PANI was polymerized with PVA to yield a semi‐IPN. The total flux and water flux increased systematically, whereas the selectivity decreased greatly from 251.87 to 5.95 with increasing amounts of water in the feed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1968–1978, 2005     

Synthesis and characterization of hybrid membranes using poly(vinyl alcohol) and tetraethylorthosilicate for the pervaporation separation of water–isopropanol mixtures

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis and cocondensation reaction for the pervaporation separation of water‐isopropanol mixtures. The resulting membranes were characterized by Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and differential scanning calorimetry. The glass transition temperature of these membranes varied from 100 to 120°C with increasing TEOS content. Effects of crosslinking density and feed compositions on the pervaporation performances of the membranes were studied. The membrane containing 1.5:1 mass ratio of TEOS to PVA gave the highest separation selectivity of 900 at 30°C for 10 mass % of water in the feed mixture. It was found that the separation selectivity and permeation flux data are strongly dependent on the water composition of the feed and operating temperature. However, the membrane with the highest crosslinking density showed unusual pervaporation properties. The overall activation energy values were calculated using the Arrhenius‐type equation. The activation energy values for the permeation and diffusion varied from 49.18 to 64.96 and 55.13 to 67.31 kJ/mol, respectively. Pervaporation data have also been explained on the basis of thermodynamic quantities. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1304–1315, 2004     

Pervaporation separation of water‐isopropanol mixtures using polymeric membranes: Modeling and simulation aspects

Pervaporation technique was used to separate water + isopropanol azeotropic mixtures at 30°C using pure sodium alginate, pure poly(vinyl alcohol), and blend membranes of sodium alginate containing 10 and 20 mass % of poly(vinyl alcohol). The membrane performance was studied by calculating flux, selectivity, pervaporation separation index, and enrichment factor. Pure sodium alginate membrane gave the highest pervaporation separation index for all compositions of water. Pervaporation experiments were carried out for 10 mass % containing water + isopropanol mixture at 30, 40, and 50°C. The Arrhenius activation parameters were computed. The PV results have been analyzed by considering complete mixing and plug flow models. Design parameters, like membrane area, permeate concentrations, flux, stage cut, separation selectivity, etc., have been calculated for different feed compositions of water in the mixture. Results are explained in terms of sorption‐diffusion principles. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1143–1153, 2005     

Effect of operation conditions in the pervaporation of ethanol–water mixtures with poly(1‐trimethylsilyl‐1‐propyne) membranes

Poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) is known to show preferential permeation of ethanol in the pervaporation of ethanol–water mixture. Although this polymer presents good characteristics for the separation of organic–water solutions, operation conditions and membrane characteristics, such as thickness, affect its pervaporation performance. The effect of temperature and feed concentration on pervaporation was studied. During pervaporation of 10 wt % ethanol–water solution, the separation factor (α_H2O^EtOH) remains almost constant, whereas the permeation flux (F) increases exponentially with operation temperature. On the other hand, the separation factor decreases, whereas the permeation flux increases with ethanol content in the feed mixture. The membrane thickness also affects the performance of PTMSP polymer films: selectivity increases sharply with membrane thickness up to 50 μm, whereas it remains constant for thicker membranes. The permeation flux decreases with membrane thickness in the whole range studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94:1395–1403, 2004     

Permeation and separation characteristics of acetic acid/water mixtures through poly(vinyl alcohol‐g‐itaconic acid) membranes by pervaporation,evapomeation, and temperature‐difference evapomeation

In this study, itaconic acid (IA) was grafted onto poly(vinyl alcohol) (PVA) with cerium(IV) ammonium nitrate as an initiator at 45°C. The grafted PVA was characterized with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. IA‐grafted PVA membranes were prepared with a casting method, and the permeation and separation characteristics of acetic acid/water mixtures were investigated with pervaporation (PV), evapomeation (EV) and temperature‐difference evapomeation (TDEV) methods. The effects of the feed composition, operating temperature, and temperature of the membrane surroundings on the permeation rate and separation factor for the acetic acid/water mixtures were studied. The permeation rates in EV were lower than those in PV, whereas the separation factors were higher. With the TDEV method, the permeation rates decreased and the separation factors increased as the temperature of the membrane surroundings decreased. The prepared membranes were also tested in PV, EV, and TDEV to separate the various compositions of the acetic acid/water mixtures (20–90 wt % acetic acid) at 40°C. The highest separation factor, 686, was obtained in TDEV with a 90 wt % acetic acid concentration in the feed. The activation energies of permeation in PV and EV were calculated to be 8.5 and 10.2 kcal/mol, respectively, for a 20 wt % acetic acid solution. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2322–2333, 2004     

Perfluorosulfonic acid—Tetraethoxysilane/polyacrylonitrile (PFSA‐TEOS/PAN) hollow fiber composite membranes prepared for pervaporation dehydration of ethyl acetate–water solutions

Preparation of organic‐inorganic composite membranes and their pervaporation (PV) permeation and separation characteristics for the aqueous solution of ethyl acetate were described. Polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane as support membrane, the mixtures of perfluorosulfonic acid (PFSA) and tetraethoxysilane (TEOS) by the sol‐gel reaction as the coating solution, the PFSA‐TEOS/PAN hollow fiber composite membranes by the different annealing conditions were prepared. The swelling of PFSA in ethyl acetate aqueous solutions was inhibited with addition of TEOS. The PFSA‐TEOS/PAN composite membranes containing up to 30 wt % TEOS in coating solution exhibited high selectivity towards water, then the selectivity decreased and permeation flux increased with increasing the TEOS concentration more than 30 wt %. When the PFSA‐TEOS/PAN composite membranes were annealed, the separation factor increased with increasing annealing temperature and time. Higher annealing temperature and longer annealing time promoted the crosslinking reaction between PFSA and TEOS in PFSA‐TEOS/PAN composite membranes, leading to the enhanced selectivity towards water. For the PFSA/PAN and PFSA‐TEOS/PAN composite membrane with 5 and 30 wt % TEOS annealed at 90°C for 12 h, their PV performance of aqueous solution 98 wt % ethyl acetate were as follows: the separation factors were 30.8, 254 and 496, while their permeation flux were 1430, 513 and 205 g/m² h at 40°C, respectively. In addition, the PV performance of PFSA‐TEOS/PAN composite membranes was investigated at different feed solution temperature and concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of PVA membrane modified by water‐soluble hyperbranched polyester (WHBP) for the dehydration of n‐butanol

Water‐soluble hyperbranched polyester (WHBP) was synthesized through the esterification reaction of the fourth generation hyperbranched polyester and maleic anhydride. A novel cross‐linked WHBP/PVA membrane was prepared by adding WHBP into poly(vinyl alcohol) (PVA) solution with glutaraldehyde as the cross‐linker. WHBP was characterized by Nuclear Magnetic Resonance and Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR‐FTIR), while WHBP/PVA membranes were characterized by ATR‐FTIR, X‐ray Diffraction, Scanning Electron Microscopy, Thermogravimetric Analysis, mechanical capacity, and water contact angle. Testing results showed that maleic anhydride was grafted on the surface of WHBP; compared with PVA membrane, WHBP/PVA membrane had lower crystallinity, weaker mechanical strength, higher hydrophilicity, and better thermal stability. Sorption and diffusion behaviors of n‐butanol and water in WHBP/PVA membrane were investigated; pervaporation performances of WHBP/PVA membrane were studied through the dehydration of the 90 wt % n‐butanol aqueous solution at 40°C. With an increase of the WHBP content from 0 to 30 wt %, both n‐butanol uptake and n‐butanol diffusion coefficient first decreased then increased; n‐butanol flux first decreased from 10 to 2 g·m^?2·h^?1 then increased to 213 g·m^?2·h^?1; both sorption selectivity and diffusion selectivity first increased then decreased; separation factor first increased from 88 to 1309 then decreased to 16. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43533.     

Pervaporation study of water and tert‐butanol mixtures

The permeation behavior of water/tert‐butanol mixture through Sulzer Pervap2510 hydrophilic poly(vinyl alcohol) membranes was investigated and the effects of feed composition and temperature on separation efficiency of the membranes were studied. The pervaporation experiments were carried out with feed water content varying from 0 to 20 wt % according to the existing industrial needs and with the feed temperature from 60 to 100°C. Over this range, both water flux and separation factor increased with increasing water content and feed temperature. These phenomena may be attributed to (1) the strong interaction between water and the membrane, (2) the decoupling effect of the permeants and the membrane at elevated temperatures, and (3) the steric hindrance effect of branch chain alcohol. The permeability ratio (the ideal separation factor) of water to tert‐butanol across the membrane was calculated and found to follow the same relationship with increasing temperature and water content. Both flux and separation factor obtained from the Pervap2510 membrane in this study were much higher than previous reported values, possible causes for which were analyzed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4082–4090, 2004     

Preparation and characterization of layered membranes constructed by sequential redox‐initiated grafting onto polyacrylonitrile ultrafiltration membranes

Layered membranes were prepared by sequential grafting—by means of redox initiators—of water‐soluble monomers, with oppositely charged ionic groups, onto ultrafiltration (UF) polyacrylonitrile (PAN) membranes at room temperature. Grafting of a single layer of 2‐hydroxyethylmethacrylate (HEMA) onto a PAN membrane gave a highly grafted membrane with a relatively high water flux. Bilayered membranes with various properties containing poly‐2‐(dimethylamino)ethyl methacrylate (p‐2DMAEMA) as the bottom layer and polymethacrylic acid or polystyrenesulfonic acid (p‐SSA) as the upper layer were prepared and compared—by means of infrared spectroscopy and electron microscopy—with single‐layered membranes of grafted polyhydroxyethylmethacrylate. Layered membranes exhibited a significant decline in water flux in comparison with the initial UF membranes. The flux could, however, be manipulated by controlling the concentration of monomers, the time of grafting, and the number of layers. When four layers of p‐2DMAEMA and p‐SSA were sequentially grafted onto a PAN membrane, pure water fluxes were stable over a wide range of pH values and did not change over long storage times. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 509–520, 2005     

Dehydration of light oil by pervaporation using poly(vinyl alcohol)–poly(acrylic acid‐co‐maleic acid) membranes

A new blended membrane was prepared and tested by pervaporation of light oil, a mixture of five alcohols plus water. The blended membrane was synthesized by blending poly(vinyl alcohol) and poly(acrylic acid‐co‐maleic acid) sodium salt in the presence of sulfuric acid to dope the reaction. We tested several membranes in order to choose the adequate composition to have the best permselectivity. The PVA(60)–PAA‐co‐maleic acid(40) membrane was selected as it was found to be highly selective. Sorption experiments were performed using binary and ternary water–alcohol solutions. The influence of temperature and feed composition on the selectivity and flux in pervaporation was investigated for two different binary mixtures (water/ethanol, water/isobutanol) and one ternary system (water/ethanol/isobutanol). This membrane presents good permselective properties, high water flux, and good selectivity and can even be used for high‐water activities The performances of this new membrane were compared to those obtained with the PVA(90)–PAA(10) membrane synthesized recently: The fluxes observed for the water–ethanol separation were of the same order of magnitude but the selectivity was found to be much higher. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1709–1716, 2002     

Permeation and Separation Characteristics of Acetic Acid‐Water Mixtures by Pervaporation through Acrylonitrile and Hydroxy Ethyl Methacrylate Grafted Poly(vinyl alcohol) Membrane

Abstract

In this study, acrylonitrile (AN) and hydroxyl ethyl methacrylate (HEMA) were grafted onto poly(vinyl alcohol) (PVA) using cerium (IV) ammonium nitrate as initiator at 30°C. The graft copolymer was characterized using the Fourier transform infrared spectroscopy (FTIR) and elemental analysis. The grafted PVA membranes (PVA‐g‐AN/HEMA) were prepared by a casting method, and used in the separation of acetic acid‐water mixtures by pervaporation. The effects of the membrane thickness, operating temperature, and feed composition on the permeation rate and separation factor for acetic acid‐water mixtures were studied. Depending on the membrane thickness, the temperature and feed composition PVA‐g‐AN/HEMA membranes gave separation factors 2.26–14.60 and permeation rates of 0.18–2.07 kg/m²h. It was also determined that grafted membranes gave lower permeation rates and greater separation factors than PVA membranes. Diffusion coefficients of acetic acid‐water mixtures were calculated from permeation rate values. The Arrhenius activation parameters were calculated for the 20 wt.% acetic acid content in the feed using the permeation rate and the diffusion data obtained at between 25–50°C.     

Pervaporation separation of water–acetic acid mixtures through NaY zeolite‐incorporated sodium alginate membranes

The pervaporation (PV) separation and swelling behavior of water–acetic acid mixtures were investigated at 30, 40, and 50°C using pure sodium alginate and its zeolite‐incorporated membranes. The effects of zeolite loading and feed composition on the pervaporation performance of the membranes were analyzed. Both the permeation flux and selectivity increased simultaneously with increasing zeolite content in the polymer matrix. This was discussed on the basis of a significant enhancement of hydrophilicity, selective adsorption, and molecular sieving action, including a reduction of pore size of the membrane matrix. The membrane containing 30 mass % of zeolite showed the highest separation selectivity of 42.29 with a flux of 3.80 × 10^?2 kg m^?2 h^?1 at 30°C for 5 mass % of water in the feed. From the temperature dependency of diffusion and permeation data, the Arrhenius activation parameters were estimated. The E_p and E_D values ranged between 72.28 and 78.16, and 70.95 and 77.38 kJ/mol, respectively. The almost equal magnitude obtained in E_p and E_D values signified that both permeation and diffusion contribute equally to the PV process. All the membranes exhibited positive ΔH_s values, suggesting that the heat of sorption is dominated by Henry's mode of sorption. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2101–2109, 2004     

pH‐ and temperature‐sensitive in vitro release of salicylic acid through poly(vinyl alcohol‐g‐acrylamide) membranes

In this study, acrylamide (AAm) was grafted onto poly(vinyl alcohol) (PVA) in solution with UV radiation, and membranes were prepared from the graft copolymer (PVA‐g‐AAm) for transdermal release of salicylic acid (SA) at in vitro conditions. Permeation studies were carried out using a Franz‐type diffusion cell. Release characteristics of SA through PVA and PVA‐g‐AAm membranes were studied using 2.0 mg/mL SA solutions. Effects of the presence of AAm in the copolymer, pH of donor and acceptor solution, and concentration of SA and temperature on the release of SA were investigated. Permeation of SA through the membranes was found to be pH‐dependent, and increase in pH generally increased the release percentage of SA, and the presence of AAm in the membrane positively affected the permeation. The effect of concentrations of SA on the permeation was also searched using saturated solution of SA, and permeated amount of SA was found to be less than in the case of unsaturated SA solution. Studies showed that the release of SA from PVA‐g‐AAm membranes was temperature‐sensitive and increase in temperature increased the permeation rate. 82.76% (w/w) SA was released at the end of 24 h at (39 ± 1)°C, and the overall activation energy for the permeation of SA through PVA‐g‐AAm membranes was found to be 19.65 kJ/mol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pervaporation separation of MTBE–methanol mixtures using cross‐linked PVA membranes

Poly(vinyl alcohol)(PVA)/poly(acrylic acid)(PAA) and PVA/sulfosuccinic acid (SSA) membrane performances have been studied for the pervaporation separation of methyl tert‐butyl ether (MTBE)/methanol (MeOH) mixtures with varying operating temperatures, amount of cross‐linking agents, and feed compositions. Typically, the separation factor, about 4000, and the permeation rate, 10.1 g/m²/h, were obtained with PVA/PAA = 85/15 membrane for MTBE/MeOH = 80/20 mixtures at 50°C. For PVA/PAA membranes, it could be considered that the flux is affected by the structural changes of the membranes due to the cross‐linking and the free carboxylic acid group also took an important role in the separation characteristics through the hydrogen bonding with PVA and the feed components leading to the increase of flux. The latter membrane of the 5% SSA membrane shows the highest separation factor of 2095 with the flux of 12.79 g/m²/h for MTBE/MeOH = 80/20 mixtures at 30°C. Besides the swelling measurements were carried out for pure MTBE and MeOH, and MTBE/MeOH = 90/10, 80/20 mixtures using PVA/SSA membranes with varying SSA compositions. It has been recognized that there are two factors, the membrane network and the hydrogen bonding in the swelling measurements of PVA/SSA membranes. These two factors act interdependently on the membrane swelling. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1699–1707, 2000