The transport phenomena of some model solutes through postcrosslinked poly(2-hydroxyethyl methacrylate) membranes with different tactic precursors

Two series of membranes of various degree of hydration have been prepared by postcrosslinking highly syndiotactic and isotactic poly(2-hydroxyethyl methacrylate) [P(HEMA)] with various amounts of hexamethylene diisocyanate (HMDIC). The equilibrium water content, the partition coefficient, and the permeability of the model solutes such as urea, acetamide, NaCl, 2-propanol, and isobutanol for these membranes were measured. In addition, differential scanning calorimetry (DSC) study for the membranes was performed. The membranes of the isotactic precursor are more hydrated at 25°C compared to the ones of its syndiotactic counterpart. This may be due to the more hydrophobic nature of syndiotactic P(HEMA). The partition coefficient data show that the solutes of urea, acetamide, and NaCl are partitioned only into the water-containing region, whereas the alcohol solutes are preferentially sorbed on to polymer matrix. The permselectivity data of urea to NaCl reveal that the permselectivity of crosslinked isotactic P(HEMA), (ISO) membranes increases as the amount of HMDIC is increased from 2.5 to 10 mol %, while the trend is reversed for crosslinked syndiotactic P(HEMA), (SYN) membranes. The apparent diffusivity order of urea, acetamide, and NaCl is not the same in those two characteristic membranes: the order is urea > NaCl > acetamide for highly crosslinked ISO membranes, and NaCl > urea > acetamide for all SYN membranes, which was compared with the free diffusion data in aqueous solution and interpreted in terms of the water-structural orderlines within membranes.     

Plasma deposition modified nylon 4 membranes for hemodialysis

The purpose of this research is to prepare high solute permeability membranes for hemodialysis by plasma depositing hydrophilic monomers onto chemically treated or O₂ plasma etched Nylon 4 substrate. The factors that affect the performances of membranes, such as deposition conditions and chemical or plasma etching conditions, were studied. The monomers used in this study were 1-vinyl-2-pyrrolidone (VP), 2-Hydroxyethyl methacrylate (HEMA), and Methyl methacrylate (MMA). The permeabilities of NaCl, urea, vitamin B₁₂, and albumin were measured, as were the water content, hydration, diffusivity, partition coefficient, and protein adsorption ratio of fibrinogen to albumin by membrane surface of plasma deposited membranes. The permeabilities of NaCl, urea, vitamin B₁₂, and albumin of HEMA 5 w-1 h plasma deposited onto chemical treated Nylon 4 membranes were 2.896 ± 0.192, 3.301 ± 0.325, 0.010 ± 0.007, and 0.000 x 10^?5 cm²/min, respectively. The mole ratio of adsorbed fibrinogen to adsorbed albumin (F/A) is 0.26 ± 0.05, which is much lower than that of the pure Nylon 4 membrane (0.94 ± 0.06) and the Gambro® membrane (0.90 ± 0.15). The HEMA deposited membrane possesses the highest feasibility as hemodialysis material among those plasma deposited membranes considered.     

HEMA‐grafted chitosan for dialysis membrane applications

Chitosan was graft copolymerized with HEMA (2‐Hydroxyethylmethacrylate) for the development of blood‐compatible dialysis membranes. The permeation characteristics of HEMA‐grafted chitosan films for four different solutes creatinine, urea, glucose, and albumin was studied in vitro at 37°C for assessment of the suitability as dialysis membranes. The grafted film CH‐12.5 composition (425% grafting) showed very high permeation to creatinine by reaching the equilibrium within 45 min. The compositions CH‐7.5 and CH‐12.5 showed excellent permeation to glucose when compared to virgin chitosan films. In the case of urea permeation, all the grafted compositions exhibited higher percent permeation than the virgin chitosan films. The copolymer films CH‐7.5 and CH‐12.5 showed enhanced permeability for the high molecular weight solute, albumin. The other grafted copolymer compositions followed almost the same trend as that of chitosan for the low molecular weight solutes as well as the high molecular weight solute. The copolymer films were also found to be highly blood compatible, noncytotoxic, and biodegradable. Hence, the need for developing blood‐compatible chitosan membranes with desirable permeability properties is achieved by the graft copolymerization of HEMA onto chitosan. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2960–2966, 2006     

Influence of degree of grafting and grafting temperature on the permeabilities of grafted polypropylene membranes

Polypropylene dialysis membranes were prepared using cobalt-60 gamma radiation to directly graft 2-hydroxyethyl methacrylate (HEMA) onto polypropylene (PP) membranes. The surface structures of both the grafted membranes and the PP membrane were observed by using FTIR–PAS and ESCA methods. The X-ray diffraction diagrams of the PP and PP-g-HEMA membranes indicated a transformation process of the β-form toward the α-form crystallinity with increasing degree of grafting. The SEM data of the membrane grafted under a low grafting temperature showed many spheres of PHEMA embedded in the PP matrix, whose size was well distributed and increased with the degree of grafting. The influences of the degree of grafting and grafting temperature on the permeabilities of PP-g-HEMA membranes toward urea and creatinine were studied in a dialyzer. In all cases, the PP-g-HEMA membrane obtained under higher grafting temperature showed higher permeability toward those solutes. The permeation coefficients of urea and creatinine through the PP-g-HEMA membrane obtained at 59°C were about 10.4 and 28.8 times that through the PP membrane, respectively. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:83–89, 1998     

Fabrication of efficient pervaporation desalination membrane by reinforcement of poly(vinyl alcohol)–silica film on porous polysulfone hollow fiber

Pervaporation membrane technology is commercially successful in the dehydration of organic solvents, and the technology has potential for seawater desalination with high recovery because of its capability to treat highly saline water. But to make the technology advantageous over the other available membrane desalination technologies in terms of productivity flux without additional energy cost, the selective barrier layer is required to be extremely thin, defect‐free, hydrophilic, and selective to water. In this work, we prepared an efficient membrane by reinforcing a highly water‐permeable but continuous barrier layer of poly(vinyl alcohol)–silica (PVA‐SiO₂) hybrid material on porous polysulfone hollow fibers. The PVA‐SiO₂ in acidified and hydrated ethanol was aged at room temperature for a period to allow solvent evaporation to obtain the solution concentration desired for the reinforcement. The reinforced hollow fiber membrane with optimal PVA‐SiO₂ barrier layer thickness exhibited a performance with a flux of 20.6 L m^?2 h^?1 and 99.9% salt rejection from a saline feed of 2000 ppm NaCl at 333 K. The effects of PVA‐SiO₂, temperature, and feed salinity on the pervaporation performance of the membrane were also studied. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45718.     

Reverse osmosis separations for some alcohols and phenols in aqueous solutions using aromatic polyamide membranes

The performance of aromatic polyamide membranes for reverse osmosis separations of eight alcohol and four phenol solutes in dilute aqueous solutions has been studied. The Taft polar parameter σ^* for the solutes studied were in the range of ?0.3 to 1.388. Positive solute separations were obtained for each one of the solutes. In the σ^* value range of ?0.3 to 0, data on PR/PWP ratio scattered close to 1, and solute separation decreased with increase in σ^*. For the phenol solutes, PR/PWP ratio decreased and solute separation increased with increase in σ^*. The results are interpreted on the following basis. The aromatic polyamides are more nonpolar than cellulose acetates. In the σ^* range of ?0.115 to ?0.3, solute separation is governed primarily by polar interactions; in this range, solute transport parameter D_AM/Kδ is well correlated by the expression D_AM/Kδ = C^* exp (ρ^*σ^*). The solute separation for ethyl and methyl alcohol solutes (σ^* = ?0.1 and 0, respectively) is reduced by the nonpolar character of the membrane material. Positive solute separation for each of the phenolic solutes is due to preferential sorption of solute at the membrane-solution interface caused by both the nonpolar character of the membrane material and acidity of the solutes.     

Parameters for prediction of reverse osmosis performance of cellulose acetate propionate membranes

Data on reverse osmosis separations have been obtained for 12 alkali metal halide solutes and 24 organic solutes (including eight alcohols, four aldehydes, seven ketones, and five ethers) with cellulose acetate propionate (CAP) membranes using single-solute dilute aqueous feed solutions at 250 psig. From the analysis of these data, the parameters and correlations needed to calculate the values of solute transport parameter D_AM/Kδ for the above classes of inorganic and organic solutes for a CAP membrane of any surface porosity from data on D_AM/Kδ for NaCl only have been generated. These parameters and correlations enable one to predict reverse osmosis separations of different solutes included in the classes of compounds studied in this work, from a single set of experimental data on membrane specifications given in terms of pure water permeability constant and D_AM/Kδ for NaCl. The reverse osmosis characteristics of CAP material lie intermediate between those of cellulose acetate and aromatic polyamide materials reported in the literature.     

Correlation of the solubility of volatile liquids in molten polymers

The solubility of volatile liquids at infinite dilution (i.e., in the Henry's law region) in poly(vinyl acetate) (PVAc) and polystyrene (PS) at elevated temperatures has been correlated by plotting ln(1/K_p) against (T_c/T)², where T_c is the critical temperature of the solute and K_p is Henry's constant at temperature T and a total pressure of approximately at 1 atm, defined as P₁ = K_pV₁⁰, where P₁ is the partial pressure of the solute in the vapor phase and V₁⁰ is the solubility (cm³ solute per g polymer at 273.2 K and 1 atm). For this correlation, we have used experimental data available in the literature for 16 solutes covering 81 data points for PVAc and 17 solutes covering 82 data points for PS. We have calculated values of 1/K_p from the literature data reported in terms of the retention volume V_g⁰, weight-fraction Henry's constant H₁, and activity coefficient at infinite dilution Ω₁^∞. We have made the following observations: (1) for PVAc, ln(1/K_p) = ?1.564 + B(T_c/T)²; and (2) for PS, ln(1/K_p) = ?2.028 + B(T_c/T)². In both cases, we found that values of B, the slope in the ln(1/K_p) versus (T_c/T)² plots, vary with the acentric factor ω of the solutes. It has been found that, in both PVAc and PS at the same value of ω, values of B for slightly polar aromatic solutes are larger than those for nonpolar aliphatic solutes. Further, in PS at the same value of ω, values of B are smaller for strongly polar solutes than for slightly polar solutes, whereas in PVAc the opposite trend holds. This observation may be interpreted as that the solubility of strongly polar solutes in a polar polymer (e.g., PVAc) is greater than that of slightly polar and nonpolar solutes, whereas the solubility of strongly polar solutes in a nonpolar polymer (e.g., PS) is less than that of slightly polar solutes but greater than that of nonpolar solutes. The dependence of B on ω, observed in this investigation, is at variance with the correlations reported by Tseng, Lloyd, and Ward for PVAc and by Stiel and Harnish for PS.     

Nylon 4/HEMA chemical homografted membrane

To enhance the degree of grafting, homografting copolymerization of 2-hydroxyethyl methacrylate (HEMA) onto nylon 4 using a chemical initiator has been attempted. The factors that affect the grafting copolymerization are the concentration of reactants, reaction time, and temperature. The dialysis permeabilities of solutes, water content, surface energy, mechanical properties, and blood compatibility of the membrane were investigated. Under the same reaction conditions, the degree of grafting by the homografting method is remarkably higher than of the heterografting method for the nylon 4–HEMA grafting system. The dialysis permeabilities of NaCl, vitamin B₁₂, and ovalbumin of the homografted membrane with a 14.8% degree of grafting are 2.760, 0.392, and 0.073 × 10^?5 cm²/min, respectively. These permeabilities are higher than the corresponding ones of ungrafted nylon 4 membrane. The mol ratios of adsorbed fibrinogen/albumin (F/A) of the heterografted membranes were found to decrease from 0.53 to 0.33, and the surface energy, to increase from 40.6 to 46.4 dyn/cm with the degree of grafting in the range of 12.5–29.9%, and their relationship is not remarkable for the homografted membranes for which the mol ratios of F/A are about 0.22–0.32 with the degree of grafting in the range of 14.8–103.8%. Observed from scanning electron micrographs of the membrane surface, denseness was found to be important to improve blood compatibility. Based on the dialysis permeabilities of solutes and the blood compatibility observed in this study, the homografted nylon 4/HEMA membrane can be considered as a hemodialysis material.     

Prediction of isobaric and isothermal vapour–liquid equilibria from limited experimental data

Malesinski's method for prediction of isobaric vapour–liquid equilibrium data using a single experimental datum on a T–x isobar has been modified and extended to a more general case where the molar entropies of vaporisation of the components are not necessarily equal and the non-ideality in the vapour phase is considered. However, it is assumed that the solution behaves like a strictly regular one over the temperature range in question, that is, the constant A in the expression for excess free energy: g^E=Ax₁x₂ is independent of temperature. The method has been illustrated for several systems and is found to be highly satisfactory for non-polar–non-polar as well as polar–non-polar systems in which the boiling points of the pure components are not much different. Incorporating temperature dependence of the constants in the Redlich–Kister equation for excess free energy, a method has been developed for predicting isothermal vapour–liquid equilibrium data at several temperature levels from equilibrium values at a single pressure. For testing the validity of this method, predicted results have been compared with the available experimental data for zeotropic as well as azeotropic systems comprising non-polar–non-polar, polar–non-polar and polar–polar mixtures, and the method has been found to be satisfactory for all systems.     

Polyether-segmented nylon hemodialysis membranes. IV. Membrane morphologies and permeability characteristics of dialysis membrane composed of poly(ethylene oxide)-segmented Ny69/M10

Dialysis membrane was prepared by a phase inversion method using a new polyether-segmented nylon which dissolves in common organic solvents such as dimethylsulfoxide. The polyether-segmented nylon contained poly(ethylene oxide) block and nylon block (random copolyamide: Ny69/M10) prepared by sebacic acid, azelaic acid, m-xylenediamine, and hexamethylenediamine. The morphologies and permeability characteristics of the membranes were investigated. It was shown by scanning electron microscope observation that the membrane had a fingerlike structure when dimethylsulfoxide was used as a polymer solvent, and a spongelike structure when an additive such as calcium chloride was added to the polymer solution. The high permeability for the solutes such as urea and vitamin B₁₂ were observed in comparison with the polyether-segmented Ny610 membranes prepared by a phase inversion method. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1731–1737, 1997     

Plasma-modified Nylon 4 membrane for dialysis

The effects of plasma treatment conditions, such as supply power, treatment time, gases used in reactor, surface energy, water content, dialysis permeability, partition coefficient, diffusion coefficient, and free volume of Nylon 4 membranes, were studied. The solutes considered for dialysis system were NaCl, urea, and MgCl₂. The permeabilities of NaCl and urea of membranes with plasma treated in argon at 80 W for 20 min are 5.57 × 10^?5 and 5.89 × 10^?5 cm²/min, respectively. Much higher permeabilities of NaCl and urea obtained by oxygen plasma-treated membranes under 20 W and for 20 min are 30.74 × 10^?5 and 17.66 10^?5 cm²/min, respectively, compared to that of untreated Nylon 4 membranes.     

Poly(hydroxyethyl methacrylate‐co‐glycidyl methacrylate) reactive membrane utilised for cholesterol oxidase immobilisation

Poly(2‐hydroxyethyl methacrylate‐co‐glycidyl methacrylate) p(HEMA–GMA) membrane was prepared by UV‐initiated photopolymerisation of 2‐hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) in the presence of an initiator, azobisisobutyronitrile (AIBN). Cholesterol oxidase was immobilised directly on the membrane by forming covalent bonds between its amino groups and the epoxide groups of the membrane. An average of 53 µg of enzyme was immobilised per cm² of membrane, and the bound enzyme retained about 67% of its initial activity. Immobilisation improved the pH stability of the enzyme as well as its temperature stability. The optimum temperature was 5 °C higher than that of the free enzyme and was significantly broader. The thermal inactivation rate constants for free and immobilised preparations at 70 °C were calculated as k_{i (free)} 1.06 × 10^?1 min^?1 and k_{i (imm)} 2.68 × 10^?2 min^?1, respectively. The immobilised enzyme activity was found to be quite stable in the repeated experiments. © 2002 Society of Chemical Industry     

Combination of chemical oxidation‐membrane filtration processes for the elimination of phenyl‐ureas in water matrices

BACKGROUND: Phenyl‐urea herbicides are found in surface waters and wastewaters as a consequence of their extensive use in agriculture. Due to their pollutant power, the removal of phenyl‐ureas is a priority objective in water treatment technologies. RESULTS: Four selected phenyl‐ureas herbicides (linuron, diuron, chlortoluron and isoproturon), dissolved in two water matrices (a groundwater and and a reservoir water), were subjected to sequential combinations of chemical treatments and membrane filtration processes. Two specific sequences were conducted: first, a chemical oxidation stage (where UV radiation, ozone and ozone plus hydrogen peroxide were used) followed by a nanofiltration process; and second, a membrane filtration stage (using UF and NF membranes) followed by an ozonation stage. Values for the herbicide removals in the oxidation stages and for the rejection coefficients in the filtration stages are provided, and the partial contribution of the different stages is established for each combined treatment. CONCLUSIONS: High removals (over 80%) were reached for phenyl‐ureas elimination by most of the combined processes tested. In the combined chemical oxidation/nanofiltration processes, the most effective was an ozonation pretreatment ([O₃]₀ = 1.5 mg L^?1)) followed by a NF step. In the opposite sequence filtration/chemical oxidation, the most effective was a NF pretreatment followed by the ozonation ([O₃]₀ = 2 mg L^?1). Copyright © 2009 Society of Chemical Industry     

The rejection of polar organic solutes in aqueous solution by an interpolymer anionic composite reverse osmosis membrane

Reverse osmosis separation for many kinds of polar organic solutes (alcohols, phenols, monocarboxylic acids, amines, and ketones) was examined by an anionic charged composite membrane. The solute permeation was carried out in single-solute aqueous solution (200 mg/L) under applied pressure of 7.88 MPa at 25°C. The correlation between the solute rejection and polar parameters for these organic solutes have been investigated. For n-alkyl alcohols, monocarboxylic acids, and ketones, the solute rejection increases with molecular weight and/or molecular branching. For undissociable polar organic solutes such as alcohols and ketones, solute rejections are closely related with the Taft's number. For dissociable polar organic solutes, solute rejections depend greatly upon the dissociation constant and the degree of dissociation of solute. This membrane showed higher rejection (80%) for phenol in an undissociated state at a 98% rejection level of NaCl. Also, rejections of phenolic derivatives depend upon the pH value of the feed solution and the polar effect of substituted groups. For acetic acid and methylamine, the solute rejection increases proportionally to the degree of dissociation of solute. From these facts, the main factors in reverse-osmosis separation by an anionic composite membrane are discussed.     

Novel Co‐Mn‐O nanosheet catalyst for CO preferential oxidation toward hydrogen purification

Co‐Mn‐O composite oxide nanosheet catalyst was successfully prepared using a facile urea‐assisted one‐step hydrothermal method in the absence of organic or organic templating reagent. Co‐Mn‐O nanosheet catalyst was optimized by varying hydrothermal process parameters such as molar ratio of Co‐Mn to urea, hydrothermal temperature, and hydrothermal time. Various characterization techniques including scanning electron microscopy, X‐ray diffraction, nitrogen adsorption, X‐ray photoelectron spectroscopy, Raman spectroscopy, and H₂ temperature‐programmed reduction were used to reveal the relationship between catalyst nature and catalytic performance in CO preferential oxidation (CO PROX) in excess H₂. The developed Co‐Mn‐O nanosheet catalyst have demonstrated much superior catalytic performance to Co‐Mn‐O nanoparticle, particularly in the low temperature range, and 100% CO conversion over the developed Co‐Mn‐O nanosheet can be achieved in temperature range of 50 to 150°C at 10,000 mL g^?1 h^?1 of gas hourly space velocity in the standard feed. Furthermore, the almost complete CO removal over Co‐Mn‐O nanosheet at 125°C of low temperature with 94.9% selectivity can be achieved even in the simulated reformed gas. The excellent catalytic performance is ascribed to nanosheet morphology, more surface Co³⁺, smaller average crystallite size, higher reducibility, and strong Co‐Mn interaction. Catalytic stability investigation indicates the developed nanostructured catalyst exhibits high catalytic stability for CO PROX reaction in simulated gas. The developed Co‐Mn‐O nanosheet catalyst can be a potential candidate for catalytic elimination of trace CO from H₂‐rich gas for Proton exchange membrane fuel cell applications. © 2014 American Institute of Chemical Engineers AIChE J, 61: 239–252, 2015     

Diffusive permeability of solutes in poly(vinyl alcohol) membranes as a function of the degree of hydration

Sorption and permeation of sodium chloride, Congo Red (a direct dye), and Sunset Yellow (an acid dye) in PVA membranes were measured to discuss the relation among the degree of hydration H, permeability P, and diffusion coefficient D. Above H of 0.9, the permeability and diffusion coefficient of various solutes could be described by free volume theory provided that the value of V^*_s/V_fw is estimated properly, where V^*_s is the ratio of critical volume of permeating molecule to vander Waals volume of water and V_fw is the free volume fraction of water. Below H of 0.9, however, Ogston's relation which predicts a linear relation between (1-H) and the logarithm of P or D fits better than the free volume relation. It seemed to indicate that the polymer networks simply had a geometrical obstruction effect in the diffusion of solutes. The diffusion coefficient extrapolated at H = 1 in Ogston's plot decreased with the increase in the interaction between solute and polymer as suggested by the partition coefficient. The hydration dependence of the partition coefficient K changed at H = 0.8 corresponding to the maximum amount of the bound water.     

Performance of cellulose acetate butyrate membranes in hyperfiltration of sodium chloride and urea feed solution

Cellulose acetate butyrate (CAB) membranes gave high salt and urea rejection with a water flux of about 3 gfd (gallons/ft² · day) during hyperfiltration at 600 psig. Evidence was obtained which indicated that the CAB membranes used in this work were asymmetric. Membrane heat treatment increased urea rejection significantly while salt rejection was invariant, and water flux decreased. An increase in feed solution temperature caused a significant increase in water flux and a small decrease in urea and salt rejection. Increasing the pressure increased water flux and urea and salt rejection. During a 400-hr life test, the water flux decreased by about 25% while urea rejection increased and salt rejection was invariant. The influence of pressure, membrane heat treatment, and compaction during CAB membranes life testing on urea and salt rejection provided evidence that these two solutes were rejected by somewhat different mechanisms. Salt rejection was consistent with a solution–diffusion mechanism for membrane transport and uncoupled flow while changes in urea rejection with pressure, membrane heat treatment, and compaction during life testing suggested that urea was at least partially rejected by membrane exclusion resulting from geometric factors.     

Studies on polyurea-amide membranes

Different polyurea-amides were synthesized by interfacial polymerization of acid chloride, diamine, and diisocyanate. The polymers and the membranes were characterized for their RO/UF applications. Highly porous membranes could be prepared from the sulfuric acid-based casting formulation and the membrane casting conditions were established. The resulting membranes are not asymmetric as they give high permeability to water and salt solutions. They are found to be resistant to many organic solvents, thus making them useful in concentration/separation applications. Whole milk, egg albumin and Na-alginate were found to be rejected 100% by these membranes, while solutes of about 20,000 M_w are found to be rejected to the extent of 70-80%.     

Advantages of a Polyimide Membrane Support in Nonhumidified Fluorohydrogenate‐Polymer Composite Membrane Fuel Cells

We have successfully prepared composite membranes consisting of the ionic liquid N‐ethyl‐N‐methylpyrrolidinium fluorohydrogenate and the polymer 2‐hydroxyethylmethacrylate and have secured them on a polyimide (PI) membrane support. The resulting EMPyr(FH)_1.7F–HEMA (9:1 molar ratio) composite possesses ionic conductivity of 75 mS cm⁻¹ at 120 °C when a 16‐µm support is employed, showing improved performance with elevated temperature; this marks a significant difference from devices using conventional polytetrafluoroethylene supports. In the single cell test, a maximum power density of 31 mW cm⁻² is observed at 120 °C. Cross‐sectional SEM images of the corresponding membrane electrode assemblies reveal no significant difference in membrane thickness before and after cell testing, implying that this support does not suffer from membrane softening issues.