Separation of liquid mixtures by using polymer membranes. III. Grafted poly(vinyl alcohol) membranes in vacuum permeation and dialysis

A series of poly(vinyl alcohol) membranes were modifed by radiation-induced graft copolymerization with acrylic acid and methacrylic acid monomers. These grafted poly(vinyl alcohol) membranes were then tested for their separation and permeability characteristics in vacuum permeation and dialysis experiments. The permselectivity of the membranes toward methanol and water was studied on a vacuum permeation apparatus at 30, 40, and 50°C. The permeation process was found to be a temperature-activated process. The logarithm of the permeation rate varied linearly with the reciprocal of the absolute temperature. The permeability of the grafted membranes was found to increase with the degree of grafting, with no appreciable selectivity toward water in binary mixtures. The acrylic acid-grafted membranes generally showed greater improvement in permeability than the methacylic-grafted membranes. The permeability of the grafted membranes toward methanol, sodium chloride, urea, creatinine, and uric acid was studied in a dialyzer. In all cases, the grafted membranes showed an improved permeability toward these solutes over the commercial poly(vinyl alcohol) membranes. The dialysis results were then compared with those obtained for dialysis-grade cellophane membranes. For the case of sodium chloride, urea, and methanol, the permeability of the grafted membranes was comparable to that of cellophane. A comparison of commercial and grafted poly(vinyl alcohol) membranes in their permeability toward ionic solutes exhibited somewhat anomalous behavior in that the permeability of the commercial membranes was higher than that of the grafted membranes. This related to the ionic nature of the modified membrane. The permeability coefficients determined in the dialysis experiments were found to be directly related to the degree of hydration of the grafted membrane. This behavior was attributed to changes in the size and shape of voids within the membrane structure.     

Grafting of acrylamide to Nylon-6 by the electron beam preirradiation technique

Summary In water swollen nylon grafted acrylamide (NYgAM) membranes, prepared by the electron beam preirradiation technique, water was classified into three categories: bound, free and intermediate states. The partition of water into these states was evaluated by utilising the data of water sorption capacity and permeability coefficients of water and ionic solutes through the membranes. Reevaluation of the partition was done utilizing the data of water proton relaxation times T_i, measured by pulsed NMR technique. The partition was evaluated as follows: the first 2 moles of water per mole of grafted polyacrylamide (PAM) are bound, the next 4/3 moles are intermediate and the rest of the water is free. It was further found that in highly water swollen membranes, the water beyond 2 moles per mole of PAM can be classified as free water.     

Grafting of acrylamide to nylon-6 by the electron-beam preirradiation technique. II. Kinetic aspects and film permeability

Single- and multilayered laminated nylon-6 films were grafted with acrylamide (AM) using the electron-beam preirradiation technique. Very high grafting yields were obtained within short time periods. Grafting onto single films was shown to proceed via “diffusion free” pseudo zero-order kinetics. Grafting onto multilayered films was diffusion controlled. SEM and EDAX measurements indicate uniform grafting of single-film membranes and asymmetric grafting of membranes prepared by grafting onto multilayered films. The permeability of grafted membranes to a number of permeants was found to increase with extent of grafting. The specific permeability to both water and solutes exceeded that of the dialysis grade cellophone at 500% graft. The selectivity of grafted films towards various solutes had also been found to be higher than that of cellophane.     

Quaternary salts as solubilization site modifiers of organic compounds in anionic micellar solutions

The effects of the addition of different salts (quaternary bromides or NaBr) on the viscosity (measured under Newtonian flow conditions) of sodium dodecylbenzenesulfonate (SDBS) micellar solutions were studied at 30°C. Tetra-n-butylammonium bromide (Bu₄NBr) was found most effective in increasing the viscosity (due to possible change in micellar shape) at fairly low SDBS concentration (50 mM). The effectiveness of Bu₄NBr may be due to the presence of four butyl chains and to the positive charge on its counterion (Bu₄N⁺) which can subsequently interact with anionic SDBS micelles electrostatically as well as hydrophobically; owing to solubility/steric problems, other salts were ineffective. Organic additives such as cyclohexylamine and cyclohexanol had marginal effects on viscosity when added to 50 mM SDBS solutions having no Bu₄NBr. However, in the presence of Bu₄NBr, the effect was dependent on salt concentration and the nature of the additive. The overall effect is discussed on the basis of change in the solubilization site of the additive in the presence of Bu₄NBr.     

Grafting of acrylamide to nylon-6 by electron beam preirradiation. IV. Sorption of water in nylon grafted acrylamide membranes

Membranes prepared by extensive grafting of acrylamide onto nylon-6 films exhibit high water sorption capacity. Swelling of the membranes increases after treatment with aqueous solutions of formic acid. Sorption of water into these annealed membranes reaches values of ca. 25 moles of water per mole of grafted acrylamide. The sorption characteristics of the swollen membrane-gels crosslinked with bis-acrylamide were explored. Membranes grafted with acrylamide, crosslinked with bis-acrylamide and annealed with formic acid reach the maximum swelling capacity at low graft yields.     

Grafting onto Tedlar films by the electron beam preirradiation technique

Summary Polyvinylfluoride (Tedlar) films, 12.5m and 25m thick, were grafted with acrylamide monomer (AM) in a mixed solvent of water and tetrahydrofurane (THF), following preirradiation with a 550 kV electron beam accelerator. The highest graft yields were attained with AM/THF/H₂O solutions in which the concentration of THF was in the range of 40–50% (w/w) . At this range, the graft yield rise with grafting period was almost linear, and graft yields of 600%. and higher were attained at AM concentration of 30% within 12–15 min without significant gelation of the solution. Water permeation rates through the Tedlar films were increased, upon grafting with AM, by a factor of up to 500. Water permeation rates through the Tedlar grafted with acrylamide (TEDgAM) films, grafted in solutions containing at least 30%. THF, were high and comparable with those of cellophane films or nylon grafted acrylamide films (NYgAM) of comparable thickness, implicating that the Tedlar film cross-section has been completely penetrated through by the grafted copolymer. The highest rates of water permeability were observed in TEDgAM films grafted in monomer solutions which contained 60%. THF.     

Preparation of thermosensitive cellophane-graft-N-isopropylacrylamide copolymer membranes and permeation of solutes through the membranes

Thermosensitive membranes with high mechanical strength were prepared by heterogeneous graft copolymerization of N-isopropylacrylamide (NIPAAm) onto cellophane in a nitric acid solution using cerium ammonium nitrate as an initiator, and the permeation behavior of solutes such as lithium chloride and poly(ethylene glycol)s (PEGs) through the membranes at various temperatures was investigated. The degree of graft copolymerization of NIPAAm on cellophane depended on temperature, time, initiator concentration, and so on. The copolymer membranes having a high content of the NIPAAm moiety could be obtained at 25°C for 24 h. The permeation of Li⁺ through the membranes was affected by temperature, i.e., the permeation rate of Li⁺ increased with increasing temperature up to 32°C and then decreased rapidly above 35°C. The permeation rate of Li⁺ through the copolymer membranes at 40°C decreased considerably, but that at 20°C decreased slightly with an increasing amount of the NIPAAm moiety in the membranes. The permeation rate of PEGs with a molecular weight more than 1000 through the cellophane-g-NIPPAm copolymer membranes was considerably suppressed and only the permeation rate of PEG300 increased with increasing temperature up to 35°C and then decreased at 40°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 209–216, 1997     

Permeability of solutes through cellophanes grafted with vinyl monomers. II. Diffusion of potassium chloride through cellophanes grafted with acrylic acid

The permeability behavior of potassium chloride through cellophane grafted with acrylic acid by a γ-irradiation method was studied by the theoretical equation derived from the phenomenological equation and compared with the results of Donnan membranes equilibrium. It was shown that the permeation of potassium chloride through the grafted cellophanes exhibited behavior typical of a polyionic membrane for grafts of more than 55% but depended on the permeability of both cellophane and graft regions for lower percents of grafting. It was found that the dominant factor affecting the permeation of potassium chloride was an effective concentration of fixed charge in the membrane.     

Effect of Quaternary Ammonium Salts on Carrier-Mediated Transport of Lanthanide Ions through Cellulose Triacetate Membranes

Abstract

Fluxes of all lanthanides, except promethium, across cellulose triacetate membranes were determined by using mixtures of o-nitrophenyl n-octyl ether and quaternary ammonium salts as plasticizers, and 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone (BMPP) and 4-trifluoroacetyl-3-methyl-1-phenyl-5-pyrazolone (TMPP) as carriers. The quaternary ammonium salts used were didodecyldimethyl-, distearyldimethyl-, tetrahexyl-, tetraoctyl-, and tetradecylammonium bromides [referred to as (C₁₂)₂NBr, (C₁₈)₂NBr, (C₆)₄NBr, (C₈)₄NBr, and (C₁₀)₄NBr, respectively]. The effect of these ammonium bromides on the flux was demonstrated. For membranes containing 0.1 M (C₁₂)₂NBr and (C₁₈)₂NBr, BMPP exhibited considerably high fluxes. The fluxes of lanthanum and cerium using BMPP for (C₁₂)₂NBr were higher than those of the other lanthanides. For the membranes containing 0.5 M (C₁₂)₂NBr and 0.1 M (C₁₈)₂NBr, however, no difference in flux among the lanthanides was observed. The fluxes using TMPP for (C₁₂)₂NBr and (C₁₈)₂NBr were very small, with the exception of some lanthanides. Appreciably high fluxes were observed for membranes containing 0.1 M (C₆)₄NBr using BMPP. For (C₈)₄NBr and (C₁₀)₄NBr, BMPP exhibited low fluxes. For these membranes using TMPP, the lanthanides were scarcely transported.     

Preparation and permeability of solutes through acrylic acid-g-methylcellulose copolymer membranes

Graft copolymer membranes from the methylcellulose and the acrylic acid were prepared and their properties and the permeability of four solutes were estimated. Acrylic acid-g-methylcellulose (AA-g-MC) copolymer dissolved in aqueous acetone solvent was cast to prepare membranes followed by the subsequent crosslinking either with aluminium potassium sulfate or by the thermal-curing method. The equilibrium water content in the membrane increased with the volume fraction of acetone in the aqueous acetone solvent system. Membrane, the ionically crosslinked with the aluminum potassium sulfate, showed the water content in the range of 38.5 and 58.4% and 0.25–0.33 kg/mm² of the tensile strength in the wet state. Compared with ionically crosslinked membranes, thermally dried membranes exhibited a more dense structure, resulting in lower water contents and higher mechanical strength. Experimental results on the permeation of four small and midsize solutes through the graft copolymer membranes revealed the molecular weight dependence of the permeability coefficient. The higher the degree of swelling, the greater the permeability coefficient. Ionically crosslinked membranes had higher solute permeability than the commercial Cuprophane membrane had. © 1993 John Wiley & Sons, Inc.     

Small-angle neutron scattering studies on sodium dodecylbenzenesulfonate-tetra-n-butylammonium bromide systems

A phase study was completed on aqueous sodium dodecylbenzenesulfonate (SDBS) and tetra-n-butyl-ammonium bromide (Bu₄NBr) systems, and consolute boundaries were drawn through cloud points. Samples were selected from both miscibility regions [under the lower consolute boundary (LCB) and above the upper consolute boundary (UCB)] for small-angle neutron scattering (SANS) studies. In the first set of experiments, the effect of varying Bu₄NBr concentration on micellular parameters of 100 mM SDBS was studied at 30°C. The pure SDBS micelle has an aggregation number (n _s ) of 51, and the effective charge on the monomer (α) is 0.17. With the addition of Bu₄NBr, the n _s of SDBS micelles increases while α decreases. The system with [Bu₄NBr]=39.5 mM (an above-UCB sample) showed clouding near room temperature (≈29°C) and had a high n _s value (300) and a low α (=0.09). The data indicated that the micelles lose ionic character in the presence of Bu₄NBr. The temperature effect on this sample shows that α remains almost constant, while n _s decreases on heating. A similar effect was observed with samples of lower Bu₄NBr concentration (32 or 25 mM) in the presence of 100 mM SDBS. The same type of temperature effect was seen on a sample of under-LCB region (50 mM SDBS+32 mM Bu₄NBr); the n _s values increased significantly as the LCB was approached. The overall SANS observations suggest that the micelles have low ionic character together with high n _s values (a case of micellar growth) near LCB/UCB.     

Separation of liquid mixtures by using polymer membranes. II. Permeation of aqueous alcohol solutions through cellophane and poly(vinyl alcohol)

The permeation and separation characteristics of four different alcohol—water systems through cellophane and poly(vinyl alcohol) membranes were investigated. The homologous series of linear alcohols n-propanol, ethanol, and methanol as well as isopropanol were studied. A specially designed permeation cell was used to study permeation rates at temperatures ranging from 30° to 50°C. The dependency of both permeation and separation on the molecular size and shape of the permeating species was discussed qualitatively. The temperature dependence of the permeation rate for both pure compounds and binary mixtures was expressed by Arrhenius-type relationships. The rate was found to increase with increasing temperature while the separation decreased. Activation energies of 4–9 kcal/mole were calculated for alcohol—water solutions through cellophane, and of 8–15 kcal/through poly(vinyl alcohol). Departure of permeation rates from the ideal rates were discussed in terms of permeation “enhancement” or “depression.” These phenomena were explained in terms of both the plasticizing action of water and the “clustering” of water molecules within the polymer network.     

Plasma graft polymerization of acrylamide onto crosslinked HTPB based PU membrane for pervaporation

Pervaporation of water-ethanol mixtures through plasma graft polymerization of acrylamide onto crosslinked hydroxyl terminated poly-butadiene (HTPB) based PU membranes, plasma graft polymerization of acrylamide onto crosslinked PU membrane (AAm-p-CPU), were investigated. The grafting was dependent on the discharge power and pretreatment period. The effects of crosslinking, plasma treatment conditions, feed compositions, and feed temperature on the performance of these membranes were studied. The physical properties of crosslinked membrane were better than those of the uncrosslinked membrane. In addition, compared with crosslinked PU membranes (CPU), the plasma modified crosslinked PU membranes effectively improve the pervaporation separation performances.     

Use of radiation-grafted polyethylene in dialysis of low molecular weight metabolites

Radiation-induced graft copolymerization of styrene/maleic anhydride (Sty/MAn) binary monomers into high-density polyethylene (HDPE) has been studied. The optimum conditions under which a high grafted yield is obtained and the grafting process proceeds homogeneously have been determined. A suitable solvent for the grafting process is acetone for a (Sty/MAn) composition of (70/30 mol%). The permeability of low molecular weight metabolites (urea, creatinine, uric acid, glucose and phosphate salts) through the untreated and treated grafted HDPE membranes has been studied. The hydrophilicity of the membrane, the degree of grafting and the molecular weight and chemical structure of the metabolites have a great influence on the transport properties of the membrane. For all solutes investigated, the permeability increases with the degree of grafting. The basic metabolites show higher permeation rates through the modified membrane compared with that for the acidic metabolite, especially phosphate salts. The permeabilities of vitamin B₁₂, bovine albumin and KCl through the treated grafted membranes have been measured and those of the high molecular weight compounds are low. © 1999 Society of Chemical Industry     

Die gasdurchlässigkeit von formaldehyd-vernetztem zellglas

Permeabilites of weakly crosslinked and commercial cellophone for O₂ and CO₂ were evaluated under the condition of decreasing and increasing relative humidity. There was found a hysteresis of the permeability within a rasonable time-space of measuring. Respectively, an increased value for permeability at equal humidity of gas was obtained when coming from higher humidity. Low crosslinked cellophane shows lower effects of this hysteresis than commercial products. Differences of gaspermeability caused by hysteresis have ratios up to 6,2 times. Cellophane crosslinked by formaldehyde shows fist decreasing then increasing permeability rates with increasing content of formaldehyde. There was found a highly lowered permeability of the foils with a certain content of formaldehyde as compared with untreated cellophane. The gradient of the line showing the values of permeability plotted against the values of relative humidity of the gases in the range of 0 to 100% is decreased in a ratio of 1 : 4000 by crosslinking with formaldehyde. Tightness of crosslinked cellophane within the whole range of humidity is better than of all now known commercial-grade foils, more tight, respectively, than saran® and cellophane coated with saran® and nitrocellulose, and coated composit foils of cellophane-PE. ?Plasticizing”? crosslinked cellophane with glycerol decreases the gaspermeability further in contrast to untreated foils. The ratio of the permeabilities of CO₂ to O₂ is only slightly changed by crosslinking.     

Permeability of solutes through cellophanes grafted with vinyl monomers. I. Diffusion of potassium chloride,urea, and uric acid

The diffusive permeability of potassium chloride, urea, and uric acid through cellophanes grafted with acrylamide, acrylic acid, styrene, and N-vinyl-2-pyrrolidone by γ-ray irradiation was studied. The diffusive permeability coefficients of the permeants through the grafted cellophanes were increased with increase in hydration of the grafted membranes, except for the permeation of potassium chloride through cellophanes grafted with acrylic acid. The permeation of potassium chloride, urea, and uric acid through the various grafted cellophanes is explained by the free volume concept of homogeneously water-swollen membranes. However, the behavior of the permeation of potassium chloride through cellophane grafted with acrylic acid deviated from that of nonionic membranes because of the contribution of the electrical interaction between electrolyte and charge of the membrane.     

Grafting onto TEDLAR films by the electron beam preirradiation technique

Summary Polyvinylfluoride (tedlar) films, 12.5–25 m thick, were grafted with acrylamide monomer (AM) in an aqueous solution, following preirradiation with a 550 kV electron beam accelerator. The graft yield rose with grafting period up to 285% and 475%, for the 25 m and the 12.5 m tedlar films, respectively, and then levelled off due to gelation of the solution.Water permeation rates through the tedlar films were increased, upon grafting with AM, by a factor of up to 3. Water permeation rates through the tedlar grafted with acrylamide (TEDgAM) films were relatively low, as compared with those of cellophane films or nylon grafted acrylamide films (NYgAM) of comparable thickness, implicating that only part of the tedlar film cross-section has been penetrated through by the grafted copolymer. The highest rates of water permeability were observed in 12.5 m films grafted with 475% acrylamide.     

Pervaporation separation of ethanol–water mixtures using ionically crosslinked blended polyacrylic acid (PAA)–nylon 6 membranes

The pervaporation separation of ethanol–water mixtures was carried out through a series of ionically crosslinked polyacrylic acid (PAA)–Nylon 6-blended membranes crosslinked to varying degrees in aluminum nitrate solution. The polyacrylic acid (PAA)–Nylon 6 membranes were cast from homogeneous PAA–Nylon 6 mixtures to various thicknesses and then crosslinked. Optimum pervaporation results were obtained from crosslinked blends containing 75 wt% Nylon 6 and 25 wt% PAA. These membranes have separation factors (water/ethanol) of 35–40 at flux rates of 120–160 g/m² h. The optimum crosslinking time was found to be approximately 35 h to yield membranes with the best separation and flux rates at 25 wt% PAA content.     

Preparation and characterization of novel grafted cellophane‐phosphoric acid‐doped membranes for proton exchange membrane fuel‐cell applications

This work concerns preparation of acid‐base polyelectrolyte membranes for fuel‐cell applications from cellulosic backbones for the first time. Grafted cellophane‐phosphoric acid‐doped membranes for direct oxidation methanol fuel cells (DMFC) were prepared following three steps. The first two steps were conducted to have the basic polymers. The first step was introducing of epoxy groups to its chemical structure through grafting process with poly(glycidylmethacrylate) (PGMA). The second step was converting the introduced epoxy groups to imides groups followed by phosphoric acid (? PO₃H) doping as the last step. This step significantly contributes to induce ion exchange capacity (IEC) and ionic conductivity (IC). Chemical changes of the cellophane composition and morphology characters were followed using FTIR, TGA, and SEM analysis. Different factors affecting the membranes characters especially IEC, methanol permeability, and thermal stability were investigated and optimized to have the best preparation conditions. Compared to Nafion 117 membrane, cellophane‐modified membranes show a better IEC, less methanol permeability, and better mechanical and thermal stability. IEC in the range of 1–2.3 meq/g compared to 0.9 meq/g per Nafion was obtained, and methanol permeability has been reduced by one‐order magnitude. However, the maximum obtained IC for cellophane‐PGMA‐grafted membrane doped with phosphoric acid was found 2.33 × 10^?3 (S cm^?1) compared to 3.88 × 10^?2 (S cm^?1) for Nafion 117. The obtained results are very promising for conducting further investigations taking into consideration the very low price of cellophane compared to Nafion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Partition Coefficients of Alkyl Parabens and Ibuprofen in Micellar Systems

The partitioning of alkyl parabens and ibuprofen in aqueous solutions of nonionic and ionic surfactants is studied experimentally and via a priori predictions using the COSMO‐RS model. The effects of organic (Bu₄NBr) and inorganic (NaCl) electrolytes are examined. Addition of NaCl results in a slight increase in the partition coefficients of parabens in solutions of octylphenolpoly(ethyleneglycolether) and a more pronounced increase in the sodium dodecyl sulfate (SDS) system. The partition coefficients of ibuprofen increase on addition of NaCl to aqueous solutions of SDS and decrease if Bu₄NBr is added to dodecyl trimethyl ammonium bromide (DTAB) solutions. Good agreement between experimental and calculated data shows a high potential of COSMO‐RS in the prediction of micelle/water partition coefficients in the presence of electrolytes and makes it a valuable tool in drug and drug‐carrier design as well as in optimizing micellar reactions or micelle‐enhanced separation processes.