Sorption equilibria and diffusion coefficients of ethanol and water in the PVA membranes containing cyclodextrin

Effects of cyclodextrin (CD) on the pervaporation characteristics for water/ethanol through the PVA/CD membranes (PVA membranes containing β-CD oligomer) have been investigated in terms of sorption equilibria and diffusion coefficients based on the sorption–diffusion theory. The increase in water selectivity through the pervaporation by CD was due mainly to the changes in the diffusion coefficients by CD, which depended on the feed composition and the cross-linking time. The water selectivity through the sorption equilibria was not increased by the addition of CD, and the ethanol-sorption amount was increased by CD. These effects of CD were interpreted by the inclusion strength in the CD cavity and the cross-linking density of the PVA phase. © 1994 John Wiley & Sons, Inc.     

Sorption characterization of poly(vinyl alcohol)/chitosan interpenetrating polymer network hydrogels

Poly(vinyl alcohol) (PVA)/chitosan interpenetrating polymer networks (IPN) were prepared by UV irradiation. The water sorption behavior of the IPNs was measured at various temperatures and humidity levels. The water uptake of IPN13 is greater than that of other IPNs. Vapor sorption behavior is more affected by the density of water vapor than by hydrophilic properties with increasing temperature. Equilibrium water uptake increases as humidity increases, and the increase is more noticeable at high humidity. The sorption system of all IPNs is a relaxation‐controlled mechanism at a relative humidity (RH) of 90%, but it is a Fickian diffusion‐controlled mechanism when the RH is below 50%. With an increase in humidity, the diffusion coefficients were found to increase due to greater penetration of water into the IPNs. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 86–90, 2003     

Development and evaluation of pH-dependent interpenetrating network of acrylic acid/polyvinyl alcohol

The objective of the present work was to synthesize interpenetrating networks (IPNs) of acrylic acid/polyvinyl alcohol (AA/PVA) by free radical polymerization using N,N-methylenebisacrylamide (MBAAm) and glutaraldehyde as cross-linkers. The IPNs were evaluated for swelling, diffusion coefficient and network parameters by using Flory–Huggins theory, i.e., the average molecular weight between cross-links (M _c), polymer volume fraction in swollen state (V _2,s), number of repeating units between cross-links (M _r) and cross-linking density (N). It was found that the degree of swelling of AA/PVA interpenetrating network increases greatly within the pH range 5–7 depending on composition. The gel fraction and porosity increased by increasing the concentration of AA or PVA, while by increasing the degree of cross-linking, porosity decreased and gel fraction increased. Selected samples were loaded with chlorpheniramine maleate as a model drug. Drug release was studied in USP, hydrochloric acid buffer solution of pH 1.2 and phosphate buffer solutions of pH 5.5 and 7.5. Drug release data were fitted into various kinetics models, e.g., zero-order, first-order, Higuchi and Peppas models. The results of the kinetics investigation showed that the drug release from IPNs followed non-Fickian diffusion. Fourier transform infrared spectra confirmed the formation of cross-linked IPNs as there was a shifting to lower frequency of 1,713–1,718 cm^?1 with reduced intensity, while scanning electron microscopy revealed uniform distribution of drug in IPNs.     

SORPTION BEHAVIOR AND PRELIMINARY PERVAPORATION RESULTS OF CROSS-LINKED POLYVINYLALCOHOL AND POLYDIMETHYLSILOXANE MEMBRANES PREPARED FOR THE SEPARATION OF WATER-ETHYLACETATE MIXTURES

Since pervaporation process is the coupling of solution and diffusion mechanisms, a sorption study was carried out with membranes prepared by cross-linking polyvinylalcohol (PVA) and polidimethylsiloxane (PDMS). Tartaric acid (Tac) was used as the cross-linking agent for PVA, and a commercial cross-linking agent was used for PDMS. Sorption experiments were carried out at 30-50°C temperature range in pure water and ethyl acetate using the films prepared. The PVA and PDMS films prepared preferentially sorb water and ethylacetate, respectively. A pervaporation study at 30°C was carried out for pure ethylacetate and pure water, and mixtures of ethylacetate containing 2 and 2.5 wt% water using 100 μm thick PVA membrane. The results indicate that the PVA membrane prepared is extremely selective for water.     

Sorption behavior and preliminary pervaporation results of cross-linked polyvinylalcohol and polydimethylsiloxane membranes prepared for the separation of water-ethylacetate mixtures

Since pervaporation process is the coupling of solution and diffusion mechanisms, a sorption study was carried out with membranes prepared by cross-linking polyvinylalcohol (PVA) and polidimethylsiloxane (PDMS). Tartaric acid (Tac) was used as the cross-linking agent for PVA, and a commercial cross-linking agent was used for PDMS. Sorption experiments were carried out at 30-50°C temperature range in pure water and ethyl acetate using the films prepared. The PVA and PDMS films prepared preferentially sorb water and ethylacetate, respectively. A pervaporation study at 30°C was carried out for pure ethylacetate and pure water, and mixtures of ethylacetate containing 2 and 2.5 wt% water using 100 w m thick PVA membrane. The results indicate that the PVA membrane prepared is extremely selective for water.     

Effect of degree of cross-linking on swelling and on drug release of low viscous chitosan/poly(vinyl alcohol) hydrogels

In the present work, a series of cross-linked LVCS/PVA hydrogels with various feed compositions were prepared using glutaraldehyde as cross-linking agent. The prepared hydrogels were used for dynamic and equilibrium swelling studies. The swelling behavior of these hydrogels was investigated as functions of effect of pH, polymeric compositions and degree of cross-linking. Swelling studies were performed in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing PVA contents in the structure of hydrogels in solutions of higher pH values. This is due to the presence of more hydroxyl groups (–OH) in the PVA structure. On the other hand, by increasing LVCS contents, swelling increased in a solution of acidic pH and it is due to ionization of amino groups (–NH₂), but this swelling was not significant. Swelling of hydrogels was decreased with increase in cross-linking ratio due to tighter hydrogel structure. Porosity and sol–gel fraction were also investigated. It was found that with increase in LVCS and PVA contents porosity and gel fraction increased, whereas by increasing glutaraldehyde content gel fraction increased and porosity decreased. Diffusion coefficient (D) and network parameters, i.e., the average molecular weight between cross-links (M _C), solvent interaction parameters (χ), polymer volume fraction in swollen state (V _2S) and cross-linked density (q) were calculated using Flory–Rehner theory. Selected samples were loaded with model drug diphenhydramine HCl. The release of diphenhydramine HCl was studied for 12 h period in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5 and 7.5. It was observed that drug release increased with increasing PVA contents in the hydrogels, while release of drug decreased as the ratio of cross-linking agent increased in the hydrogel structure owing to strong physical entanglements between polymers. The release mechanisms were studied by fitting experimental data to model equations like zero order, first order, Higuchi and Peppas. Results showed that the kinetics of drug release from hydrogels in buffer solutions of pH 1.2, 5.5 and 7.5 was mainly non-fickian diffusion. Hydrogels were characterized by Fourier transform infrared and X-ray diffraction to confirm the structure and study the crystallinity of hydrogel, respectively.     

Morphology and water affinity of superabsorbent hydrogels composed of methacrylated cashew gum and acrylamide with good mechanical properties

This paper comprises the characterization of superabsorbent hydrogels based on methacrylated cashew gum (CGMA) co-polymerized with acrylamide (AAm) by measuring of the water uptake, water retention capacity in dependence of time, morphological and mechanical properties. The morphological features of hydrogels were evidenced by SEM images. Stress measurements of hydrogels as a function of temperature were considered as being the necessary force for compressing the hydrogels at 1 mm deformation. Stress-strain modeling was used to obtain the compressive elastic modulus and apparent cross-linking density of superabsorbent hydrogels. Hydrolyzed CGMA-co-AAm hydrogels showed highly water absorbing. Another remarkably feature of these hydrogels is the efficiency in the water retaining that was caused by increasing in CGMA content. Higher temperature leads to an enhancement in the stress values of superabsorbent hydrogels because the large content of water that penetrates into superabsorbent hydrogels and expands their polymer network. The increase in the amount of CGMA and AAm were accompanied by an increasing on the apparent cross-linking density of hydrogels. This contributed to increase their elastic modulus, which is inherent to a more rigid structure.     

Preparation and characterization of biocompatible spongy cryogels of poly(vinyl alcohol)–gelatin and study of water sorption behaviour

Porous biocompatible spongy hydrogels of poly(vinyl alcohol) (PVA)–gelatin were prepared by the freezing–thawing method and characterized by infrared and differential scanning calorimetry. The prepared so‐called ‘cryogels’ were evaluated for their water‐uptake potential and the influence of various factors, such as the chemical architecture of the spongy hydrogels, pH and the temperature of the swelling bath, on the degree of water sorption by the cryogels was investigated. It was found that the water sorption capacity constantly decreased with increasing concentration of PVA while initially an increase and thereafter a decrease in swelling was obtained with increasing amounts of gelatin in the cryogel. The water sorption capacity decreased with an increase in the number of freeze–thaw cycles. The hydrogels were also swollen in salt solutions and various simulated biological fluids and a fall in swelling ratio was noticed. The effect of the drying temperature of the cryogel on its water sorption capacity was also investigated, and a decrease in swelling was obtained with increasing temperature of drying. The biocompatibility of the prepared materials was assessed by in vitro methods of blood‐clot formation, platelet adhesion, and per cent haemolysis. It was noticed that with increasing concentration of PVA and gelatin the biocompatibility increased, while a reduced biocompatibility was noted with an increasing number of freeze–thaw cycles. Copyright © 2005 Society of Chemical Industry     

Effects of mixed solvent on gelation of poly(vinyl alcohol) solutions

The relationship between the polymer–solvent interaction and gelation behavior of poly(vinyl alcohol) (PVA) solutions prepared from ethylene glycol/water (EG/water) mixed solvents was investigated using a viscometer, light scattering, FTIR, X‐ray, and pulsed NMR analyses. The viscometric result showed that the affinity to PVA for water is higher than that for EG. The light scattering result showed that the spinodal decomposition rate of the PVA solution decreases rapidly as the water content in the EG/water mixed solvent is increased. On the other hand, the FTIR and X‐ray results both indicated that the crystallinity of the PVA gel decreases with water content. These results imply that the water molecules must improve the affinity of the solvent to PVA to inhibit the aggregation or crystallization of PVA chains. The pulsed NMR measurement results showed that the spin–spin relaxation times related to the polymer‐rich and polymer‐poor phases of the PVA gel increase, and the fractional amount of the polymer‐poor phase increases while that of the polymer‐rich phase decreases with increasing water content. These facts indicated that the increase in the mobility of PVA chains must give rise to the difficulty in chain aggregation of PVA solutions with increasing water content. Two transition temperatures were found in the phase transition of the polymer‐rich phase. The lower transition temperature was attributed to the destruction of the denser chain entanglements in the polymer‐rich phase and the higher transition temperature was mainly concerned with the melting of the crystallites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1113–1120, 2001     

Water sorption of poly(methyl methacrylate): 2. Effects of crosslinks

Glassy crosslinked networks were made by copolymerization of methyl methacrylate both with ethylene glycol dimethacrylate and with triethylene glycol dimethacrylate, using a redox initiator. Residual monomer was largely or wholly removed by extraction with water, by heating at 100°C, or by γ-irradiation. Water sorption conformed approximately to Fick's laws but with a retarded swelling component which increased with crosslink density. Approximate values were obtained for apparent diffusion coefficients both in sorption and desorption. The pattern of results was similar for both dimethacrylate systems. Values of diffusion coefficients were little influenced by crosslink density up to a dimethacrylate feed of 50 wt%. The saturation value for water uptake increased with increasing feed of dimethacrylate to more than twice the value for the linear polymer, i.e. poly(methyl methacrylate).     

Preparation of PVA membranes containing β-cyclodextrin oligomer (PVA/CD membrane) and their pervaporation characteristics for ethanol/water mixtures

Poly(vinyl alcohol) (PVA) membranes were modified by introducing β-cyclodextrin (β-CD) oligomer, which has an inclusion ability sensitive to size, structure, and hydrophilicity of the guest molecule. The modified membranes (PVA/CD membrane) were prepared by casting of the aqueous solutions of PVA and β-CD oligomer. The CD oligomer was immobilized in the membranes by cross-linking with glutaraldehyde. The cross-linking times were 1 and 8 h. The content of CD in the membranes was 33 wt %. The effects of CD on the pervaporation characteristics for water/ethanol were investigated by comparisons with those of the cross-linked PVA membranes. For the 1 h cross-linked membranes, CD increased both the water permeation rate and selectivity at lower ethanol concentrations in the feed. At higher ethanol concentrations, CD increased the water selectivity, but it decreased the water permeation rate. For the 8 h cross-linked membranes, at lower ethanol concentrations, CD increased the water permeation rate, but the water selectivity through the PVA/CD membrane was almost equal to that of the PVA membrane. At higher ethanol concentrations, CD increased the water selectivity and decreased the water permeation rate. These effects of CD can be interpreted in terms of the inclusion strength in the cavity and the reduction of the cross-linking density of the PVA phase in the membranes. © 1994 John Wiley & Sons, Inc.     

Synthetic absorbent for dyestuffs based on gamma crosslinked poly(vinyl alcohol) (PVA)

This work reports on the characterization and uses of gamma radiation‐crosslinked poly(vinyl alcohol) (PVA) films as absorbents for different classes of dyestuffs normally released from textile factors. Dyestuffs were selected from different producers. These dyestuffs were Remacryl Blue (basic dye), Remazol Golden Orange (reactive dye), Solar Orange (direct dye), and Sandolan (acid dye). The percentage dye sorption by PVA was determined by spectroscopic analysis and color‐strength measurements of the PVA films after absorbing the different dyestuffs. The results showed that the concentration of dimethylbisacrylamide as a crosslinking agent has a great effect on the gel fraction and percentage swelling in water of the PVA polymer. In general, crosslinked PVA showed a low tendency to absorb the different dyestuffs under investigation at room temperature. This tendency was shown to increase with an increasing temperature of the dye solution from room temperature to 70°C. Meanwhile, the highest percentage of dye sorption was found in the case of the basic dye and the lowest one in the case of the reactive dye depending on the active groups on the dyes. Moreover, the percentage dye sorption by PVA was slightly higher in the acid medium rather than in the alkaline one. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 349–354, 2003     

Water sorption and water‐resistance properties of poly(vinyl alcohol)/clay nanocomposite films: Effects of chemical structure and morphology

A series of poly(vinyl alcohol)/sodium montmorillonite (PVA/NaMMT) nanocomposite films were prepared via a solution method, and their water sorption and water‐resistant properties were investigated as a function of clay content. The water sorption and water resistance properties were strongly dependent on the chemical structure and film morphology originating from the NaMMT content. The water diffusion coefficient and water uptake of the PVA/NaMMT nanocomposite films were obtained by best fits to a Fickian diffusion model. The diffusion coefficient and water uptake in the PVA/NaMMT nanocomposite films varied between 8.16 × 10⁻¹⁰ and 3.60 × 10⁻¹⁰ cm² s⁻¹ and 35.6 and 29.9 wt%, respectively. Both the diffusion coefficient and water uptake decreased as the content of NaMMT in pure PVA was increased. Additionally, the water resistance pressure (mm) of the PVA/NaMMT nanocomposite films increased with increasing NaMMT content. Contact angle analyses showed that the chemical affinity to water and the surface energy of the nanocomposite films decreased with increasing NaMMT content. Furthermore, the well‐dispersed and exfoliated structure in the nanocomposite films not only induced an increased tortuous path for water molecules to pass through, but also increased the molecular order. However, to enhance the water sorption properties and water resistance of hydrophilic PVA, further studies to increase the dispersion of clay particles and ensure desired morphological qualities such as crystallinity and molecular packing order in the PVA/clay nanocomposite films are required. POLYM. COMPOS., 36:660–667, 2015. © 2014 Society of Plastics Engineers     

Studies on the sulfonation of poly(phenylene oxide) (PPO) and permeation behavior of gases and water vapor through sulfonated PPO membranes. III. Sorption behavior of water vapor in PPO and sulfonated PPO membranes

Water vapor absorption and desorption by poly(phenylene oxide) (PPO) and sulfonated PPO (SPPO) membranes were studied at a constant temperature of 30°C and over a broad range of water activity (0.05 ≤ a < 0.8) by the weighing method. The experimental sorption isotherms of both PPO and SPPO possessed a general sigmoidal shape, which suggested that they belong to type II; thus, the data may be quantitatively analyzed according to the BET or GAB equation for multilayer sorption processes. The number of site-bound water molecules per monomeric unit was increased by a factor of 150 after sulfonation of PPO. The features of the reduced absorption and desorption curves of both PPO and SPPO suggested that the sorption processes were non-Fickian. The diffusion coefficient calculated from the slope of the initial linear part of the curves showed concentration dependence. The permeability of water vapor through SPPO was more pressure-dependent than was that through PPO. The Flory–Huggins interaction parameter derived from experimental data on SPPO had a smaller value compared with that of PPO and was a monotonic increasing function of water activity in the low-activity region and then leveled off at a > 0.6, showing a corresponding initial decrease of the polymer–water interaction, which then gradually reached a certain stable value. Water clustering for SPPO was much less than that for PPO, which is clear proof of its higher hydrophilicity. The results from this study showed that SPPO could be an excellent dehumidification membrane material. © 1994 John Wiley & Sons, Inc.     

Mixed matrix membranes prepared from natural rubber/poly(vinyl alcohol) semi-interpenetrating polymer network (NR/PVA semi-IPN) incorporating with zeolite 4A for the pervaporation dehydration of water-ethanol mixtures

The pervaporation dehydration of water-ethanol mixtures was investigated using the mixed matrix (MM) membranes prepared from natural rubber (NR) and crosslinked poly(vinyl alcohol) (PVA) semi-IPN embedded with the zeolite 4A. With the presence of NR as well as zeolite, the swelling of MM membranes in water was effectively suppressed. Examined by DSC, the non-freezing bound water in the MM membranes was found decreasing with more zeolite loading because the water-polymer interaction is diminishing. The sorption study of MM membranes revealed a preferential sorption to water with improved water sorption selectivity as increasing the zeolite loading. For pervaporation at 5 vol% water in feed, the reversed trade-off with respect to the zeolite loading was encountered such that the total permeation flux increased along with an enhancement of the water separation factor. For higher feed water concentration, despite the greater total permeation flux, the separation factor was reduced owing to the extensive swelling of the polymer matrix. The temperature dependency of the partial water and ethanol fluxes followed the Arrhenius relationship and the estimated activation energies for water flux were lower than those of the ethanol flux, suggesting that the developed MM membranes are highly water selective.     

Sorption and permeation properties of water and ethanol vapors in poly[bis(trifluoroethoxy)phosphazene] (PTFEP) membranes

The permeability and solubility for water and ethanol in PTFEP membranes were determined experimentally, and the data were analyzed by the solution-diffusion model. The permeability for water and ethanol ranged from several hundreds to several thousands Barrers, and they increased exponentially with the vapor activity and increased with temperature. At the same temperature and vapor activity, the permeability ratio between water and ethanol ranged from 5.7 to 2.3, and it decreased as the vapor activity increased. The sorption isotherms for water and ethanol were fitted by the Henry’s law relationship. The solubility decreased as the temperature increased so that the heat of sorption for both water and ethanol was negative. The solubility for water was more than twice the solubility for ethanol. The solubility seems to be inversely proportional to the molecular size of the penetrants in such a system. The solubility ratio between water and ethanol is smaller than their molecular volume ratio possibly due to the slightly stronger nonpolar interaction and the higher degree of plasticization in the ethanol-polymer system. The diffusivity for water and ethanol ranged from 10⁻⁸ to 10⁻⁷ cm²/s, and the values for water were larger than those for ethanol at the same temperature and vapor activity. The diffusivity for water and ethanol also increased exponentially with the vapor activity. The diffusivities for water and ethanol increased with temperature and their activation energies of diffusion were very similar possibly due to the same energy characteristic of polymer main chain movement.     

In situ characterization of moisture sorption/desorption in thin polymer films using optical waveguide spectroscopy

The kinetics of moisture sorption/desorption in poly(terephthalate-co-phosphate) thin films was investigated in situ at T = 25 °C using optical waveguide spectroscopy (OWS). At low water activities, Fickian diffusion was observed for the initial phase of the sorption process, while at high activities, due to the clustering of water, a complex sorption behavior was found. The moisture sorption isotherms were analyzed according to both the Zimm and Lundberg model as well as the Brown model, which suggests the formation of clusters of water molecules in poly(terephthalate-co-phosphate) at water activities of α₁ = 0.58 or higher. The water diffusion coefficient decreases with increasing water activity, which also suggests water cluster formation. A biphasic desorption behavior was also observed upon decreasing the water activity from α₁ = 1 to 0. This study demonstrated the unique advantages of OWS in characterizing in situ the sorption/desorption behavior of penetrants in polymer thin films.     

Preparation and characterization of high strength and high modulus PVA fiber via dry-wet spinning with cross-linking of boric acid

To improve the mechanical properties of polyvinyl alcohol (PVA) fibers, a series of PVA fibers were prepared via dry-wet spinning with cross-linking of boric acid (BA) (PVA/BA fibers), and using the mixed solvent of dimethyl sulfoxide and water. Moreover, the final PVA/BA fibers were characterized by Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), differential scanning calorimetery (DSC), thermogravimetric analyzer (TGA), powder X-ray diffraction (XRD) and yarn strength tester. Furthermore, with the increasing of BA content, FTIR analysis showed that the degree of crosslinking of BA with PVA increased. SEM images of final PVA/BA fibers presented smooth surfaces, and the diameters decreased firstly and then increased. DSC, TGA, and XRD analysis indicated that the melting temperatures, thermal properties and crystallinities first increased and then decreased with the increasing of BA content. In addition, mechanical properties measurements illustrated that the cross-linking existed at an optimal BA content of 0.3 wt%, and PVA/BA-0.3 fiber had the highest tensile strength and Young's modulus of 13.1 ± 0.4 and 360.2 ± 10.4 cN/dtex, respectively.     

Preparation and characterization of polyvinyl alcohol based biomaterials: Water sorption and in vitro blood compatibility study

Semi‐interpenetrating polymer networks (semi‐IPNs) based on polyvinyl alcohol (PVA) and crosslinked polyacrylamide (PAM) were prepared by redox polymerization and further characterized by FTIR, ESEM, and XRD techniques. The semi‐IPNs of varying compositions were investigated for their water sorption behavior, and the network parameters like average molecular weight between crosslinks (M_C) and crosslink density were evaluated from water imbibition measurements. The semi‐IPNs were also judged for their in vitro blood compatibility by blood clot formation and percent hemolysis test. It was noticed that the chemical architecture exert a profound effect on the over all performance of the biomaterials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2402–2408, 2006     

Property analysis of triglyceride-based thermosets

Triglycerides with acrylate functionality were prepared from various oils and model triglycerides. The triglyceride-acrylates were homopolymerized and copolymerized with styrene. The cross-link densities of the resulting polymer networks were predicted utilizing the Flory-Stockmayer theory. Although the model predictions overestimated the cross-link density, the trends in the cross-link density predictions matched the experimental results. In both cases, the cross-link density was found to increase gradually at low levels of acrylation and then linearly at higher levels of acrylation. The deviation in the experimental results and model predictions were the result of intramolecular cross-linking. Approximately 0.5 and 0.8 acrylates per triglyceride were lost to intramolecular cyclization for homopolymerized triglyceride-acrylates and triglycerides copolymerized with styrene, respectively. The glass transition temperature (T_g) increased approximately linearly with the cross-link density from as low as −50 °C to as high as 92 °C. Simple models accurately predicted the effect of cross-link density on T_g. The tensile strength and modulus of triglyceride-based polymers increased exponentially at low levels of acrylate functionality, but increased linearly at higher levels of acrylate functionality, as predicted by vector percolation theory.