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     

Gas permeation through water‐swollen polysaccharide/poly(vinyl alcohol) membranes

The effect of Na‐alginate content on the gas permeation properties of water‐swollen membranes prepared by varying Na‐alginate and poly(vinyl alcohol) (PVA) content in membranes was investigated. The influences of water content and crystallinity of the membranes on the gas permeation performance of the water‐swollen membranes were studied. The gas permeation rate and selectivity of Na‐alginate/PVA water‐swollen membranes were compared with those of the dry membranes. The permeation rates of nitrogen and carbon dioxide through water‐swollen membranes were in the range of 0.4–7.6 × 10^?7 to 3.7–8.5 × 10^?6 cm³ (STP)/cm² s^?1 cmHg^?1, which were 10,000 times higher than those of dry‐state membranes. The permeation rates of mixture gases through water‐swollen Na‐alginate/PVA membranes were found to increase exponentially with the increase of Na‐alginate content, whereas carbon dioxide concentration in permeates was decreased linearly. It was found that the gas permeance of the water‐swollen membranes increased with increasing the Na‐alginate content in the membrane. Gas permeation rates of the water‐swollen Na‐alginate/PVA membranes increased with increasing the water content in the membrane and decreasing the crystallinity of the membrane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3225–3232, 2004     

Network characterization and swelling behavior of chemical hydrogels based on acid‐containing poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) was modified with phthalic and succinic anhydrides to give vinyl alcohol–vinyl ester copolymers that contain carboxylate groups. These half‐esters were then crosslinked by using the poly‐ (ethylene glycol) (PEG) 400 diglycidylether. Low crosslinker/carboxylate ratios were used to obtain low degrees of crosslinking, so the capacity of the resulting hydrogel to absorb water was high. Water absorption was determined gravimetrically as a function of time at room temperature. The equilibrium swelling ratio and compressive modulus were characterized for all the resulting PVA hydrogels and related to the network structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3026–3031, 2003     

Modification of poly(vinyl alcohol) membranes using sulfur-succinic acid and its application to pervaporation separation of water–alcohol mixtures

For the purposes of the water-selective membrane material development for pervaporation separation, we crosslinked poly(vinyl alcohol) (PVA) with sulfur-succinic acid (SSA), which contains —SO₃OH, by heat treatment and investigated the effect of the crosslinking density on the separation of water–alcohol mixtures by pervaporation technique. The crosslinking reaction between PVA and SSA was characterized through Fourier transform infrared spectroscopy and differential scanning calorimetry tests by varying the amount of the crosslinking agent, the reaction temperature, and the swelling measurements of each pure component. The separation performance of the water–methanol mixture is not good due to the existence of sulfonic acid, hydrophilic group, in the crosslinking agent. However, for the water–ethanol mixture, the flux of 0.291 kg/m²h and the separation factor of 171 were obtained at 70°C when PVA-crosslinked membrane containing 7 wt % SSA was used. The same membrane also showed flux of 0.206 kg/m²h and a separation factor of 1969 at the same operating temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1717–1723, 1998     

辐照法制备聚乙烯醇水凝胶研究进展

简要评述了聚乙烯醇水凝胶的制备方法,分析了各种方法的优点和缺点,介绍聚乙烯醇辐照交联的基本原理,并展望了辐射交联聚乙烯醇水凝胶研究及应用前景.     

Preparation of chemically crosslinked gels with maleate‐denatured poly(vinyl alcohol) and its application to drug release

Maleate‐denatured poly(vinyl alcohol) (M‐PVA) was crosslinked with heating. The mechanism of crosslinking was studied with several procedures: titration, Fourier transform infrared, and solubility. The carboxyl groups of M‐PVA consisted of carboxylates and a few free carboxyl groups. The crosslink was the ester linkage between hydroxyl and carboxyl groups. Several kinds of M‐PVA tablets were prepared under different conditions: pressures of 200–600 kgf/cm² and grain sizes of 75 (pass) to 250 μm (on). The swelling behavior of these chemically crosslinked tablets was studied in a buffer solution of pH 7.4, mainly at 37°C. Moreover, the effect of temperature from 5 to 50°C and the effect of repeated swell–dry cycles on the behavior of the tablets in a buffer solution [106 μm (on), 200 kgf/cm²] were studied. The release of p‐acetamidophenol from those tablets in the pH 7.4 buffer solution was studied. The different release patterns were due to the differences in the swelling behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1178–1184, 2002; DOI 10.1002/app.10411     

Preparation and swelling properties of semi‐IPN hydrogels based on chitosan‐g‐poly(acrylic acid) and phosphorylated polyvinyl alcohol

The phosphorylated poly(vinyl alcohol) (P‐PVA) samples with various substitution degrees were prepared through the esterification reaction of PVA and phosphoric acid. By using chitosan (CTS), acrylic acid (AA) and P‐PVA as raw materials, ammonium persulphate (APS) as an initiator and N,N‐methylenebisacrylamide as a crosslinker, the CTS‐g‐PAA/P‐PVA semi‐interpenetrated polymer network (IPN) ssuperabsorbent hydrogel was prepared in aqueous solution by the graft copolymerization of CTS and AA and followed by an interpenetrating and crosslinking of P‐PVA chains. The hydrogel was characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) techniques, and the influence of reaction variables, such as the substitution degree and content of P‐PVA on water absorbency were also investigated. FTIR and DSC results confirmed that PAA had been grafted onto CTS backbone and revealed the existence of phase separation and the formation of semi‐IPN network structure. SEM observations indicate that the incorporation of P‐PVA induced highly porous structure, and P‐PVA was uniformly dispersed in the polymeric network. Swelling results showed that CTS‐g‐PAA/P‐PVA semi‐IPN superabsorbent hydrogel exhibited improved swelling capability (421 g·g^?1 in distilled water and 55 g·g^?1 in 0.9 wt % NaCl solution) and swelling rate compared with CTS‐g‐PAA/PVA hydrogel (301 g·g^?1 in distilled water and 47 g·g^?1 in 0.9 wt % NaCl solution) due to the phosphorylation of PVA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Bending behaviour of electroresponsive poly(vinyl alcohol)/poly(acrylic acid) semi‐interpenetrating network hydrogel fibres under an electric stimulus

Poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) composite fibres were prepared via solution spinning and subsequently, semi‐interpenetrating networks (SIPN) were obtained by crosslinking the fibres with glutaraldehyde. The hydrogel fibres exhibited bending behaviour under DC electric stimulation. The effects of a number of factors have been systematically studied, including the PAA content within the network, electric voltage imposed across the fibre, the fibre diameter, concentration of the crosslinking agent, pH and ionic strength of the bath solution. Our experimental results show a stable reversibility of bending behaviour under the applied electric field. The degree of bending at equilibrium and the bending speed of the hydrogel fibre increased with the intensity of the applied electric voltage and the PAA content having negatively charged ionic groups within the SIPN. The electroresponsive behaviour of the present SIPN hydrogel fibre was also affected by the aforementioned extrinsic factors. These observations are interpreted in terms of fibre stiffness, fixed charge density and swelling pressure, which depend on the hydrogel equilibrium states in different pH and ionic environments together with the electrochemical reactions under DC electric field. © 2002 Society of Chemical Industry     

Poly(vinyl alcohol) and poly(vinyl amine) blend membranes for isopropanol dehydration

Blended membranes of hydrophilic polymers poly(vinyl alcohol) (PVA) and poly(vinyl amine) (PVAm) were prepared and crosslinked with glutaraldehyde. The prepared membranes were characterized using infrared (attenuated total reflection mode) spectroscopy, differential scanning calorimetry, X‐ray diffractometry, and scanning electron microscopy measurements. Pervaporation performances of the membranes were evaluated for the separation of water‐isopropanol (IPA) mixtures. As the PVAm content increased from PVAm0 to PVAm1.5, the flux through a 70 μm film increased from 0.023 to 0.10 kg/m² h at an IPA/water feed ratio of 85/15 at 30 °C. The driving force for permeation of water increased due to the temperature but it has no effect on IPA permeation. Activation energies for the permeation of IPA and water were calculated to be 17.11 and 12.46 kJ/mol, respectively. Controlling the thickness of the blend membrane could improve the permeation flux with only a marginal reduction in the separation factor. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45572.     

室温交联PVA水凝胶的制备与性能研究

以环氧氯丙烷为交联剂,采用室温化学交联法制备了聚乙烯醇(PVA)水凝胶,研究了交联温度和交联时间对PVA溶胀性能和力学性能的影响,借助差示扫描量热法(DSC)和扫描电子显微镜(SEM)对PVA水凝胶进行分析表征。结果表明,当交联时间为3d且交联温度为50℃时PVA水凝胶的综合性能最佳。PVA的玻璃化转变温度为-54.50℃,PVA水凝胶中包含有自由水、束缚水和非冷冻水。     

The water state in crosslinked poly(vinyl alcohol)–collagen hydrogel and its swelling behavior

Poly vinyl alcohol (PVA) with pendent carboxyl group was synthesized and verified. The collagen was chemical crosslinked with the produced PVA under the help of crosslinker. Then, the PVA–collagen hydrogels were prepared through the repeated freezing–thawing. Since the water states in hydrogels play an important role in the performance of the product, thermogravimetric (TG) analysis and differential scanning calorimeter (DSC) were conducted to study the different states of water. The results indicated that the weight ratio of nonfreezable water to dry gel in PVA–collagen hydrogels was about 25%. Meanwhile, the swelling behaviors in distilled water and 0.9% saline were studied. The one‐phase exponential associate equation can fit the process very well. Calculated from the simulation equation, the swelling ratios at equilibrium in distilled water and saline were 14.353 g/g dry gel and 14.205 g/g dry gel, respectively. The results illustrated that the ions in solution would decrease the swelling ratio of the hydrogel. At the same time, the lyophilization might have slighter influence to the microstructure of hydrogels and should be more suitable for the swelling research than heat drying. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characterization and determination of swelling and diffusion characteristics of poly(n‐vinyl‐2‐pyrrolidone) hydrogels in water

Hydrogels in the form of rods with varying crosslink densities and three‐dimensional network structures were prepared from Poly(N‐vinyl‐2‐pyrrolidone) (PVP)/water and PVP/water/persulfate systems by irradiation with γ rays at ambient temperature. Average molecular weights between crosslinks, percent swelling, swelling equilibrium values, diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant), and equilibrium water content were evaluated for both hydrogel systems. Water diffusion to the hydrogel is a non‐Fickian type diffusion and diffusion coefficients vary from 6.56 × 10⁻⁷ to 2.51 × 10⁻⁷cm²min⁻¹ for PVP and 6.09 × 10⁻⁷ to 2.14 × 10⁻⁷ cm²min⁻¹ for PVP/persulfate hydrogel systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 994–1000, 2000     

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     

Gelation of a new hydrogel system of atactic‐poly(vinyl alcohol)/NaCl/H2O

a‐PVA/NaCl/H₂O hydrogels have been prepared by gelation of aqueous atactic‐poly(vinyl alcohol) (a‐PVA) solutions in the presence of NaCl. The gelling temperature, melting temperature and the preservation of water of the hydrogels have been measured. The effect of the addition of NaCl to the hydrogels on gelling temperature and melting temperature is marked when the NaCl concentration is over a certain value. High NaCl concentration favours high‐melting‐point hydrogels. When the NaCl concentration is high enough (such as 11%), high‐melting‐point and white turbid opaque a‐PVA/NaCl/H₂O hydrogels can be prepared, regardless of the PVA concentration. Similarly, the low gelling temperature of a‐PVA/NaCl/H₂O solutions comes from low NaCl concentration, while high gelling temperature ranges from 50 to 70 °C when the NaCl concentration is 11%. In appearance, the types of syneresis of a‐PVA/NaCl/H₂O are χ‐type or a mixture of χ‐ and n‐types; water release of the hydrogels is slowed down by the addition of NaCl. © 2002 Society of Chemical Industry     

Enhanced oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) blended with poly(acrylic acid) for packaging applications

To enhance the oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) (PVA) and expand its food packaging applicability, five crosslinked poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blend films were prepared via esterification reactions between hydroxyl groups in PVA and carboxylic acid groups in PAA. The physical characteristics of the blends, including the thermal, barrier, mechanical and optical properties, were investigated as a function of PAA ratio. With increasing PAA content, the crosslinking density was significantly increased, resulting in changes in the chemical structure, morphology and crystallinity of the films. The oxygen transmission rate of pure PVA decreased from 5.91 to 1.59 cc m^?1 day^?1 with increasing PAA ratio. The water resistance, too, increased remarkably. All the blend films showed good optical transparency. The physical properties of the blend films were strongly correlated with the chemical structure and morphology changes, which varied with the PAA content. © 2016 Society of Chemical Industry     

Selective separation of some heavy metals by poly(vinyl alcohol)‐grafted membranes

A poly(vinyl alcohol) membrane (PVA) was modified by radiation graft copolymerization of acrylic acid/styrene (AAc/Sty) comonomers. The Cu and Fe ion‐transport properties of these membranes were investigated using a diaphragm dialysis cell. In the feed solution containing CuCl₂ or a mixture of CuCl₂ and FeCl₃, the PVA‐g‐P(AAc/Sty) membranes showed high degrees of permselectivity toward Cu²⁺ rather than toward Fe³⁺. The permeation of Cu²⁺ ions through the membranes was found to increase with decrease in the grafting yield. However, as the content of Cu²⁺ ions in the Cu/Fe binary mixture feed solutions decreased, the rate and the amount of transported Cu²⁺ through the grafted membrane decreased, with no appreciable permselectivity toward Fe³⁺. When Fe²⁺ ions were used instead of Fe³⁺ ions in the feed solution containing Cu²⁺, the transport of both Cu²⁺ and Fe²⁺ through the membrane was observed. The rate of transport of Fe²⁺ was higher than that of Cu²⁺. In addition, it was found that the selective transport of ions was significantly influenced by the pH difference between both sides of the membranes. As the pH of the feed or the received solution decreased, both Cu²⁺ and Fe³⁺ passed through the membrane and were transported to the received solution. The role of carboxylic acid and the hydroxyl groups of the grafted membranes in the transportation process of ions is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 125–132, 2000     

Preparation and electroresponsive property of poly(vinyl alcohol)/sodium alginate composite hydrogel

Poly(vinyl alcohol) (PVA)/sodium alginate composite hydrogel was prepared by solidifing the blending solution of PVA and sodium alginate, then freezing and thawing repeatedly. In the direct current electric field, the composite hydrogel in aqueous NaCl solution swelled, contracted, and bent. The gel's bending speed and maximum bending degree increased with increase in the electric field intensity and the concentration of NaCl solution. The maximum bending degree increased with increase in the sodium alginate content in the composition hydrogel. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3493–3496, 2006     

Separation characteristics of pervaporation membrane separation processes using modified poly(vinyl alcohol) membranes

Modified poly(vinyl alcohol) (PVA) membranes prepared by the ‘solution technique’ were tested for ethanol-water mixtures by varying the reaction density (X_cr = 0.05, 0.1) at various temperatures. The results are compared with those of PVA membranes (X_cr = 0.05) prepared by the technique of the GFT Company, Germany.     

PVA/PEG/TEOS杂化膜制备及性能研究

以聚乙烯醇(PVA)与聚乙二醇(PEG)共混,并与正硅酸乙酯(TEOS)进行交联反应制备杂化膜。FTIR证实杂化溶胶液发生交联反应形成共价键Si—O—C,WXRD观察表明加入TEOS改变了膜结晶度,加入PEG提高了PVA膜对乙醇/水溶液的渗透通量,但分离因子下降,随着TEOS的加入,膜的分离因子提高。在TEOS质量分数为10%时,杂化膜的分离因子达到最大。提高退火温度可以提高膜的分离因子,但通量下降。在100℃下退火12 h的杂化膜对乙醇质量分数为85%的乙醇/水溶液的分离性能最佳。     

Preparation and characterization of interpenetrating network beads of poly(vinyl alcohol)‐grafted‐poly(acrylamide) with sodium alginate and their controlled release characteristics for cypermethrin pesticide

Interpenetrating network polymeric beads of poly(vinyl alcohol)‐grafted‐acrylamide with sodium alginate have been prepared by crosslinking with glutaraldehyde. Cypermethrin, a widely used pesticide, was loaded with 80% efficiency in these hydrogel beads. The beads were characterized by Fourier transform infrared spectroscopy to confirm the grafting. Scanning electron microscopy was used to know the morphology of the beads. Equilibrium swelling experiments indicated that swelling of the beads decreased with an increase in crosslinking. The in vitro release studies were performed under static conditions and the release data have been fitted to an empirical relation to estimate the transport parameters. The diffusion coefficients have been calculated for the transport of pesticide through the polymeric beads using the initial time approximation method. These values showed decrease with increasing crosslinking as well as increasing pesticide loading. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 552–560, 2002; DOI 10.1002/app.10306