Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. II. Comparative studies on the permeation characteristics of membranes prepared from N‐methylmorpholine‐N‐oxide and cuprammonium solutions

Two kinds of regenerated cellulose membranes for hemodialysis were prepared from casting solutions of N‐methylmorpholine‐N‐oxide (NMMO) and cuprammonium (denoted NMMO membranes and cuprammonium membranes, respectively). The concentration of cellulose in the casting solution investigated was 6–8 wt %. The permeation characteristics of both membrane series were compared in terms of the ultrafiltration rate (UFR) of pure water, the sieving coefficient (SC) of dextran, and the solute permeabilities of urea, creatinine, and vitamin B₁₂. The UFR and SC of the NMMO membranes were strongly affected by the cellulose concentration of the casting solution, and NMMO was a preferable solvent for the production of cellulose membranes with high performance; the cuprammonium solution gave low‐performance membranes. The pore structures of both types of membranes were estimated with the Hagen–Poiseuille law. The results showed that the NMMO membranes had larger pore radius and smaller pore numbers than the cuprammonium membranes. The differences in the membrane pore structures led to the differences in the performance between the two membrane series. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 333–339, 2003     

Charged polyacrylonitrile membranes having amphiphilic quaternized ammonium groups for ultrafiltration

Four types of positively charged polyacrylonitriles having quaternized N,N-dimethylaminoethyl methacrylate (DAMA) were synthesized and were used to prepare ultrafiltration membranes by a phase-inversion method. The effect of aliphatic ethyl, octyl, and stearyl groups and the benzyl group, which covalently bind to the quaternary ammonium group, on filtration properties was studied by ultrafiltration under an applied pressure of 760 mmH₂O. Water permeability through the resultant membranes increased as the aliphatic chain length on the quaternary ammonium group increased. For a copolymer membrane having a benzyl group on the quaternary ammonium group, water permeability was lower than that for the ethyl type of copolymer membrane. The membrane permeability and pore size for the molecular size-exclusion effect were studied at various NaCl concentrations in the 0–0.15M region. The membranes having octyl and stearyl groups showed stable filtration behavior by increase of the NaCl concentration, while the membranes having an ethyl group and a benzyl group on the quaternary ammonium group showed a change of the water permeability due to a pore-size increase for the membrane by NaCl addition. Measurements of membrane potential indicated the shielding of positively charged sites of the membranes by salt addition. Further, the copolymer membranes showed a separation ability for water/2-butanol of low water content. The separation ability was attributed to the chemical structure of the membranes having different interaction characteristics with the mixture components. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1821–1828, 1998     

Triblock copolymers of methyl methacrylate/N‐vinyl pyrrolidone and their hydrophilication effects on poly(vinylidene fluoride) porous membranes

The new amphiphilic triblock copolymers of poly(N‐vinyl pyrrolidone‐b‐methyl methacrylate‐b‐N‐vinyl pyrrolidone) (P(VP‐b‐MMA‐b‐VP)) were synthesized via a reversible addition fragmentation chain transfer polymerization route. Using these copolymers as additives in casting solutions, the porous blend membranes of poly (vinylidene fluoride) and P(VP‐b‐MMA‐b‐VP) were prepared following a typical nonsolvent induced phase separation process. The influences of P(VP‐b‐MMA‐b‐VP) on the morphologies of the blend membranes were observed by scanning electron microscopy. The chemical compositions in membrane surface layers were measured by X‐ray photoelectron measurement. Water contact angle and water flux experiments were used to evaluate the hydrophilicity and permeation properties of the blend membranes. It was found that the P(VP‐b‐MMA‐b‐VP) copolymers could be retained in membrane stably in membrane formation and application process. The copolymers could enrich in surface layer and endowed the blend membrane with efficient hydrophilicity and higher water permeation flux. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on syntheses and permeabilities of special polymer membranes: 30. Ultrafiltration and dialysis characteristics of cellulose nitrate-poly(vinyl pyrrolidone) polymer blend membranes

The ultrafiltration and dialysis characteristics of the semipermeable polymer blend membranes obtained from cellulose nitrate, poly(vinyl pyrrolidone), and N,N-dimethyl formamide were investigated under various conditions. The water content fraction and the ultrafiltration rate were dependent on the poly(vinyl pyrrolidone) content in the membranes, and the strengths were governed by the cellulose nitrate content in the polymer blend. If the pore radius in the membranes, calculated according to the Hagen-Poiseuilli equation for capillary model, was identical, the water content in each membrane was not identical. It was found that urea molecules broke very weak hydrogen bonds of the bound water in the membrane, but sodium chloride did not, also, the diffusion of urea through the membrane was more rapid than that of sodium chloride. The ratio of the membrane diffusion coefficient to the ultrafiltration rate was explained qualitatively by the capillary model, however, when the bound water in the water content fraction was considered, this ratio showed better agreement with the model.     

Quest for high performance carbon capture membranes: Fabrication of SAPO-34 and CNTs-doped polyethersulfone-based mixed-matrix membranes

Gas separation process is an effective method for capturing and removing CO₂ from post-combustion flue gases. Due to their various essential properties such as ability to improve process efficiency, polymeric membranes are known to dominate the market. Trade-off between gas permeability and selectivity through membranes limits their separation performance. In this study, solution casting cum phase separation method was utilized to create polyethersulfone-based composite membranes doped with carbon nanotubes (CNTs) and silico aluminophosphate (SAPO-34) as nanofiller materials. Membrane properties were then examined by performing gas permeation test, chemical structural analysis and optical microscopy. While enhancing membranes CO₂ permeance, SAPO-34 and CNTs mixture improved their CO₂/N₂ selectivity. By carefully adjusting membrane casting factors such as filler loadings. Using Taguchi statistical analysis, their carbon capture efficiency was improved. The improved mixed-matrix membrane with loading of 5 wt% CNTs and 10 wt% SAPO-34 in PES showed highly promising separation performance with a CO₂ permeability of 319 Barrer and an ideal CO₂/N₂ selectivity of 12, both of which are within the 2008 Robeson upper bound. A better mixed-matrix membrane with outstanding CO₂/N₂ selectivity and CO₂ permeability was produced as a result of the synergistic effect of adding two types of fillers in optimized loading.     

Specialty polymeric membranes. V. Selective permeation of carbon dioxide through synthetic polymeric membranes having 2-(N,N-dimethyl)aminoethoxycarbonyl moiety

Permeation of CO₂ was investigated by using synthetic polymeric membranes having a tertiary amine moiety, 2-(N,N-dimethyl)aminoethoxycarbonyl moiety. Permselectivity of the present membranes towards CO₂ was achieved. Through poly{2-(N,N-dimethyl)aminoethyl methacrylate-co-acrylonitrile} (DMAEMA/AN-199) membrane, where DMAEMA mol fraction was 0.199, the separation factor towards CO₂ for CO₂/N₂ separation ranged from 60 to 90, ranging in the CO₂ partial pressure in the feed gas from 61 to 3.6 cmHg. © 1995 John Wiley & Sons, Inc.     

Atomic force microscopy of cellulose membranes prepared from the N‐methylmorpholine‐N‐oxide/water solvent system

Cellulose membranes were obtained by solutions of cellulose being cast into a mixture of N‐methylmorpholine‐N‐oxide (NMMO) and water under different processing conditions. Atomic force microscopy (AFM) was used to investigate the surface structures of the membranes. The AFM method provided information on both the size and shape of the pores on the surface, as well as the roughness of the skin, through a computerized analysis of AFM micrographs. The results obtained showed that the surface morphologies were intrinsically associated with the permeation properties. For the cellulose membranes, increasing the NMMO concentration and the temperature of the coagulation bath led to higher fluxes and lower bovine serum albumin rejection. These were always correlated with higher values of the roughness parameters and larger pore sizes of the membrane surfaces. When the cellulose concentration of the casting solution was 11 wt %, the membrane showed a nodular structure with interconnected cavity channels between the agglomerated nodules. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3389–3395, 2002     

Influence of the coagulation‐bath temperature on the phase‐separation process of poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) solutions and membrane structures

A poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) copolymer was synthesized, and flat‐sheet membranes were prepared via the phase‐inversion method with N,N‐dimethylformamide (DMF) as the solvent and water as the coagulation bath. The effects of the coagulation‐bath temperature on poly(vinylidene fluoride) (PVDF)/DMF/water and PVDF‐g‐PNIPAAm/DMF/water ternary systems were studied with phase diagrams. The results showed that the phase‐separation process could be due to the hydrophilicity/hydrophobicity of poly(N‐isopropylacrylamide) at low temperatures, and the phase‐separation process was attributed to crystallization at high temperatures. The structures and properties of the membranes prepared at different coagulation‐bath temperatures were researched with scanning electron microscopy, porosity measurements, and flux measurements of pure water. The PVDF‐g‐PNIPAAm membranes, prepared at different temperatures, formed fingerlike pores and showed higher water flux and porosity than PVDF membranes. In particular, a membrane prepared at 30°C had the largest fingerlike pores and greatest porosity. The water flux of a membrane prepared in a 25°C coagulation bath showed a sharp increase with the temperature increasing to about 30°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Pervaporation of ethanol–water mixtures through styrene-substituted N-phenylmaleimide copolymer membranes

A number of copolymers of styrene with substituted N-phenylmaleimides were synthesized and their solutions in chloroform were used in the casting of homogeneous membranes. The latter were applied in the separation of variously concentrated ethanol—water mixtures by pervaporation at 35°C. The membranes were characterized by the separation factor related to preferentially transported water and by the flux of the permeate. In contrast to membranes made from copolymers of styrene with N-phenylmaleimide, the separation factor of membranes containing substituted N-phenylmaleimides increased with increasing amount of ethanol in the feed solution. The effect of incorporated imide units on the properties of the membranes under investigation is discussed. © 1992 John Wiley & Sons, Inc.     

Polycarbonate/(N,N′-dialicylidene ethylene diamine) cobalt(II) complex membrane for gas separation

A polycarbonate/(N,N′-dialicylidene ethylene diamine) cobalt(II) (cosalen) complexed membrane was prepared by introducing oxygen carrier (cosalen) into polycarbonate for gas separation. With increasing amount of oxygen carrier in the membranes, the selectivity of O₂/N₂ increased and the permeabilities of both O₂ and N₂ decreased. The selectivity of O₂/N₂ decreased with increasing operating temperature. The pure gases sorption measurements indicated that the affinity between oxygen and the membranes was appreciable higher than that of nitrogen. According to the X-ray analysis of the complexed membranes, the decreased gas diffusivities were caused by the increase of the packing density. The selectivity of O₂/N₂ was 15 and oxygen permeability for the cobalt complexed membrane with 3 wt % oxygen carrier was 0.33 barrers at 5°C. Furthermore, a dual mode sorption mechanism was utilized to describe the behavior of gas sorption and permeation through the cobalt complexed membrane. © 1996 John Wiley & Sons, Inc.     

Separation of VOCs from N2 using poly(ether block amide) membranes

This work deals with the separation of volatile organic compounds (VOCs) from nitrogen streams for organic vapour emission control by poly(ether block amide) membranes. As representative air pollutant VOCs, n‐pentane, n‐hexane, cyclohexane, n‐heptane, methanol, ethanol, n‐propanol, n‐butanol, acetone, dimethyl carbonate, and methyl tert‐butyl ether were used in this study. The separation of both binary VOC/N₂ and multicomponent VOCs/N₂ gas mixtures was carried out, and the membranes exhibited good separation performance. A VOC concentration of more than 90 mol% was achieved at a feed VOC concentration of 5 mol%. It was found that the permeances of the VOCs were mainly dominated by their solubilities in the membrane, whereas the permeance of N₂ was affected by the presence of the VOCs. The permeance of N₂ in the VOC/N₂ mixtures was shown to be higher than pure N₂ permeance due to membrane swelling induced by the VOCs dissolved in the membrane. Nevertheless, theVOC/N₂ selectivity increased with an increase in the feed VOC concentration. Among the VOCs studied, the membrane showed a higher permeance to alcohol VOCs than paraffin VOCs. The effects of feed VOC concentration, temperature, stage cut, and permeate pressure on the separation performance were investigated.     

Polypropylene membranes with the double sensitivity effect

This article describes the modification of polypropylene membranes leading to the preparation of thermo‐ and pH‐sensitive structures. Poly(N‐isopropylacrylamide), poly(acrylic acid), or copolymer poly(N‐isopropylacrylamide‐co‐acrylic acid) was grafted on to the membranes' surface activated by dielectric barrier discharge plasma. The properties of the modified membranes were evaluated by means of infrared spectroscopy and contact angle measurements. The effect of modification was monitored by the determination of water flux at two temperatures (20 and 45°C) and at various pH values (2.8–8.0). The membrane separation properties were investigated for the solutions of o‐bromocresol purple. It was found that membranes grafted with copolymer were responsive to both stimuli and they could be used for separation purpose. The separation performance was tailored by alteration of pH and temperature of feed solution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41763.     

Electrospun fiber membranes from blends of poly(vinylidene fluoride) with fouling‐resistant zwitterionic copolymers

Nonwoven super‐hydrophobic fiber membranes have potential applications in oil–water separation and membrane distillation, but fouling negatively impacts both applications. Membranes were prepared from blends comprising poly(vinylidene fluoride) (PVDF) and random zwitterionic copolymers of poly(methyl methacrylate) (PMMA) with sulfobetaine methacrylate (SBMA) or with sulfobetaine‐2‐vinylpyridine (SB2VP). PVDF imparts mechanical strength to the membrane, while the copolymers enhance fouling resistance. Blend composition was varied by controlling the PVDF‐to‐copolymer ratio. Nonwoven fiber membranes were obtained by electrospinning solutions of PVDF and the copolymers in a mixed solvent of N,N‐dimethylacetamide and acetone. The PVDF crystal phases and crystallinities of the blends were studied using wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). PVDF crystallized preferentially into its polar β‐phase, though its degree of crystallinity was reduced with increased addition of the random copolymers. Thermogravimetry (TG) showed that the degradation temperatures varied systematically with blend composition. PVDF blends with either copolymer showed significant increase of fouling resistance. Membranes prepared from blends containing 10% P(MMA‐ran‐SB2VP) had the highest fouling resistance, with a fivefold decrease in protein adsorption on the surface, compared to homopolymer PVDF. They also exhibited higher pure water flux, and better oil removal in oil–water separation experiments. © 2018 Society of Chemical Industry     

Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. III. The relationship between the drying condition of the membrane and its permeation behavior

The effects of drying condition on the performance (ultrafiltration rate, diffusive solute permeability, and sieving) of hemodialysis membranes prepared from cellulose/N‐methylmorpholine‐N‐oxide (NMMO) solution (NMMO membrane) and cellulose/cuprammonium solution (cuprammonium membrane; the referential membrane) were studied. The drying condition investigated was the glycerin concentration of the solution, which was used to substitute glycerin for the water in the membrane before the membrane was dried. A lower glycerin concentration in the solution brought about a lower reswelling degree (water content) in the dried membrane in pure water, which resulted in a drop in the performance of the as‐cast membrane. The NMMO membrane had a high water content and a high membrane performance compared with the cuprammonium membrane when both the membranes were treated under the same drying condition. The differences in the performance between both membrane series is discussed on the basis of the results of the observation of the membrane morphology by scanning electron microscopy, the observation of the crystallinity of the membranes by wide‐angle X‐ray diffraction, and the estimation of the pore structure of the membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1671–1681, 2003     

Permeability through cellulose membranes grafted with vinyl monomers in a homogeneous system. VIII. N-vinylpyrrolidone-grafted cellulose membranes

The homogeneous grafting of N-vinylpyrrolidone (NVP) onto cellulose was carried out in a dimethyl sulfoxide/paraformaldehyde (DMSO/PF) solvent system. The diffusive permeabilities of solutes through the NVP-grafted cellulose membranes, apparent activation energy for solute permeation through them, states of water in them, and their microphaseseparated structures were investigated. The solute permeability through the grafted membranes was superior to that through the cellulose membrane cast from the DMSO/PF solution of cellulose. The total water and nonfreezing water contents of the grafted membranes were larger than those of the cellulose membrane. The difference in permeability through the membranes was not correlated quantitatively with the amount of each state of water in them. Activation energies for permeation of solutes through the grafted membranes were similar to those through the cellulose membrane. © 1994 John Wiley & Sons, Inc.     

Asymmetric membranes fabricated from poly(acrylonitrile‐co‐N‐vinyl‐2‐pyrrolidone)s with excellent biocompatibility

Poly(acrylonitrile‐co‐N ‐vinyl‐2‐pyrrolidone)s (PANCNVPs) show excellent biocompatibility. In this work, PANCNVPs with different contents of N‐vinyl‐2‐pyrrolidone (NVP) were fabricated into asymmetric membranes by the phase inversion method. The surface chemical composition of the resultant membranes was determined by Fourier transform infrared spectroscopy–attenuated total reflection. Field emission scanning electron microscopy was used to examine the surface and cross section morphologies of the membranes. It was found that the morphologies hardly change with the increase of NVP content in PANCNVP, while the deionized water flux increases remarkably and the bovine serum albumin (BSA) retention decreases slightly. Experiment of dynamic BSA solution filtration was carried out to evaluate the antifouling properties of the studied membranes. The relative flux reduction of PANCNVP membrane containing 30.9 wt % of NVP is 25.9%, which is far smaller than that of the polyacrylonitrile membrane (68.8%). Results deduce that this improvement comes from the excellent biocompatibility of NVP moieties instead of the hydrophilicity change, because the water contact angles of these membranes fluctuate between 60 and 70°. Results from the membranes using poly(N‐vinyl‐2‐pyrrolidone) (PVP) as an additive confirm that, to a certain extent, the PANCNVP membranes show the advantages of antifouling compared with the polyacrylonitrile/PVP blending membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4577–4583, 2006     

Application of jojoba wax bound to polyethylene membranes and hollow fibers in ion‐exchange and pervaporation processes

Chlorosulfonated polyethylene membranes and hollow fibers were reacted with allylic amino jojoba to bind the wax chemically to the polymer. The modified membranes and hollow fibers were then tested in the ion‐exchange and pervaporation processes, respectively. The jojoba‐bound polyethylene membranes were selective in preventing transfer of divalent ions such as Ca²⁺ and Mg²⁺, while monovalent ion such as K⁺ and Na⁺ could penetrate the membranes. The flux of the monovalent ions depended on the amount of jojoba bound to the polymer, which acted as a barrier to the ions (the monovalent ions could be eluted by acid washing). The concentration of ions (in the range of 0.05–1.0 N) in the feed solution had little effect on the flux. Preliminary results of pervaporation of a dioxane/water mixture through hollow fibers made of jojoba‐bound chlorosulfonated polyethylene show separation of the dioxane from the water with a separation factor of 6. This technique can be applied to remove residual organic solvents in the purification of industrial waste water. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 763–768, 2001     

Removal of N‐butanol from aqueous solutions by ion–exchange membranes containing organic counterions

The pervaporation of aqueous butanol solutions was investigated using thin‐film composite membranes composed of a poly(vinylidene fluoride) substrate coated with a sulfonated poly(2,6‐dimethyl‐1,4‐phenelene oxide) polymer. The polymer was ion‐exchanged with quaternary ammonium cations having aliphatic substituents of various chain lengths. The pervaporation of aqueous n‐butanol solutions using these membranes gave a permeate more concentrated in n‐butanol; therefore, they were alcohol‐selective. The separation factor increased and the permeate flux decreased as the chain lengths of the aliphatic substituents were increased. Hence, the mass‐transport properties of such membranes can be controlled or altered to yield some desired permselectivity by the introduction of a proper counterion. It was observed that the n‐butanol flux was small relative to the total flux and, therefore, the water flux dominated the total permeate flux. The degree of swelling of the membranes and its effect on membrane performance was investigated as well. As the n‐butanol content was increased, the swelling of the membranes increased greatly. High membrane swelling caused a reduction in the separation factor. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 47–58, 1999     

Gas permselection properties in silicone-coated asymmetric polyethersulfone membranes

The gas permeation properties of H₂, He, CO₂, O₂, and N₂ through silicone-coated polyethersulfone (PESf) asymmetric hollow-fiber membranes with different structures were investigated as a function of pressure and temperature and compared with those of PESf dense membrane and silicone rubber (PDMS) membrane. The PESf asymmetric hollow-fiber membranes were prepared from spinning solutions containing N-methyl-2-pyrrolidone as a solvent, with ethanol, 1-propanol, or water as a nonsolvent-additive. Water was also used as both an internal and an external coagulant. A thin silicone rubber film was coated on the external surface of dried PESf hollow-fiber membranes. The apparent structure characteristics of the separation layer (thickness, porosity, and mean pore size) of the asymmetric membranes were determined by gas permeation method and their cross-section morphologies were examined with a scanning electron microscope. The results reveal that the gas pressure normalized fluxes of the five gases in the three silicone-coated PESf asymmetric membranes are nearly independent of pressure and did not exhibit the dual-mode behavior. The activation energies of permeation in the silicone-coated asymmetric membranes may be larger or smaller than those of PESf dense membrane, which is controlled by the membrane physical structure (skin layer and sublayer structure). Permselectivities for the gas pairs H₂/N₂, He/N₂, CO₂/N₂, and O₂/N₂ are also presented and their temperature dependency addressed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 837–846, 1997     

Effect of solvents on performance of polyethersulfone ultrafiltration membranes: Investigation of metal ion separations

The new polyethersulfone (PES) based ultrafiltration membranes were formed using a two stage process of dry and wet phase inversion in non solvent coagulation bath. The effects of three different solvents such as, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and Dimethyl sulphoxide (DMSO) of 82.5% and 85% concentrations on the performance of final membranes were extensively investigated. Scanning electron microscopy (SEM) image results proved that PES membranes with an asymmetric structure were successfully formed. The number of pores formed on the top layer of PES membranes using above-mentioned three solvents was the result of the combined effect of the thermodynamic properties of the system (composition, concentrations, and phase behaviour) and membrane formation kinetics, whereas, the formation of the macroporous sub layer of those membranes was controlled by the diffusion rate of solvent–nonsolvent. The flux of pure water, membrane resistance, mechanical stability, molecular weight cut-off (MWCO) and separation performance of the PES membranes were studied. Separation of metal ions from aqueous solutions was studied for Ni(II), Cu(II) and Cr(III) using two complexing polymer ligands: polyvinyl alcohol (PVA) and poly(diallyldimethylammonium chloride) (PDDA).The separation and permeate rate (flux) efficiencies of the new membranes are compared using different solvents and different PES/solvent compositions.