Sulfonated polyphenylsulfone asymmetric membranes: Effect of coagulation bath (acetic acid‐NaHCO3/isopropanol) on morphology and antifouling properties

Sulfonated polyphenylsulfone porous asymmetric membranes, S‐PPSU with different sulfonation degrees, 21, 33, 50 wt %, were prepared by phase inversion. Two different coagulation baths were explored for asymmetric membrane preparation: acetone/isopropanol and acetic acid (AA)‐NaHCO₃/isopropanol. The latter bath allows better morphology control for the nucleation and pore formation of the membrane. Scanning electron microscopy of membranes shows that pore interconnectivity is improved, when the mixture of AA‐NaHCO₃/isopropanol was used for asymmetric S‐PPSU ultrafiltration membranes preparation. S‐PPSU asymmetric membranes show an increasing hydrophilicity with increasing sulfonation degree. Asymmetric membrane antifouling properties improve as the concentration of sulfonic groups increases in the membrane showing twice the flux recovery ratio and lower BSA protein absorption in static and dynamic flux tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44502.     

Fabrication of hollow and porous polystyrene fibrous membranes by electrospinning combined with freeze-drying for oil removal from water

A novel method was proposed to fabricate hollow and surface porous polystyrene (PS) fibrous membranes for the removal of oil from water. Spinning solutions were prepared by using camphene and tetraethoxysilane (TEOS) as pore-forming agents, and hollow PS fibers with 100–400 nm pores on the surface were fabricated by electrospinning and freeze-drying. The distribution and volatilization of camphene and TEOS, as well as the drying behavior of solvents in high relative humidity, were important factors in forming the porous structure of PS fibers. The specific surface area of obtained PS fibrous membranes was twice that of conventional electrospun PS fibrous membranes and displayed superhydrophobic properties. Moreover, the large adsorption storage space was formed due to the hollow structure and porous surface of PS fibers. The maximum oil adsorption capacity of the porous PS fibrous membrane was 105.4 g g⁻¹, and was larger than that of the conventional PS fibrous membrane after repeated five times, thus making it a promising tool for oil spill cleanups. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47262.     

Synthesis and properties of sulfonated biphenyl poly(ether sulfone) and its mixed‐matrix membranes containing carbon nanotubes for gas separation

We prepared mixed‐matrix membranes (MMMs) composed of carboxylated single‐walled carbon nanotubes (f‐SWCNTs) and a sulfonated biphenyl poly(ether sulfone) (S‐PPSU) polymer matrix. The thermal stability and properties of the pores of the S‐PPSU and f‐SWCNTs were characterized by thermogravimetric analysis and sorption isotherm curves, respectively; these showed that the surface and pore diameter decreased after the introduction of carboxyl groups to the single‐walled carbon nanotubes (SWCNTs), and the pore properties did not restore original values even when the f‐SWCNTs were preheated to 350 °C to remove carboxyl groups. The gas‐separation measurement showed that the MMMs comprised of the S‐PPSU and f‐SWCNTs possessed better gas‐separation properties than the ones composed of biphenyl poly(ether sulfone) and SWCNTs. The permeability for N₂, O₂, He, and CO₂ and the selectivity for O₂/N₂ and O₂/CO₂ were enhanced simultaneously because of the good dispersion of f‐SWCNTs and the improved interaction between the two phases. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44995.     

Development of new hybrid ultrafiltration membranes by entanglement of macromolecular PPSU‐SO3H chains: Preparation,morphologies, mechanical strength,and fouling resistant properties

The present work focuses on the preparation of Polyphenylsulfone (PPSU) membranes with enhanced antifouling surfaces through an incorporation of sulfonated Polyphenylsulfone (PPSU‐SO₃H), which acts as both, surface modifying agent and macromolecular additive. Initially, Sulfonated polyphenylsulfone (PPSU‐SO₃H) was synthesized by using chlosulfonic acid via bulk modification method. The degree of sulfonation (DS, %) of PPSU‐SO₃H was calculated by using NMR (nuclear magnetic resonance).The phase inversion technique was used to prepare all asymmetric membranes by allowing the PPSU‐SO₃H (different wt %) to entangle with the PPSU membrane matrix. All prepared membranes were characterized by using scanning electron microscope (SEM), X‐ray diffraction analysis (XRD), contact angle analysis (CA), mechanical strength analysis, molecular weight cut off (MWCO), porosity (%), mean pore size, and BSA adsorption studies. The performance efficiency of the membranes was evaluated by using BSA protein as a model foulant in terms of permeability, rejection (SR %), R_m (hydraulic resistance), R_c (cake layer resistance), R_p (pore plugging resistance), R_r (reversible fouling), R_ir (irreversible fouling), and FRR (flux recovery ratio). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41986.     

Effects of crosslinking modification on the O2/N2 separation characteristics of poly(phenyl sulfone)/poly(bisphenol A‐co‐4‐nitrophthalic anhydride‐co‐1,3‐phenylenediamine) blend membranes

A series of blend membranes of poly(phenyl sulfone) (PPSU) with poly(bisphenol A‐co‐4‐nitrophthalic anhydride‐co‐1,3‐phenylenediamine) (PBNPI) were prepared through a solution casting method. This was done to examine the permeation characteristics of oxygen and nitrogen. The effect of the PPSU/PBNPI ratio on the membrane structure and O₂/N₂ separation performance were investigated. The results show that the permeability increased remarkably with the content of PPSU, whereas the selectivity decreased slightly. To enhance the selectivity of O₂/N₂, the blend membranes were further crosslinked with a p‐xylylenediamine agent via the immersion method. According to the Fourier transform infrared analysis, the N? H group was formed on the imide group of PBNPI. Therefore, we suggest that during the crosslinking modification, the PBNPI served as a crosslinkable polymer; this resulted in increased crosslinking efficiency with PBNPI content. The high‐resolution X‐ray diffraction and melting point method results show that crosslinking modification improved the selectivity with an acceptable loss in permeability along with increased crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Swelling behavior and pervaporation properties of new composite membrane systems: Porous polyethylene film‐poly(acrylic acid) hydrogel

A new type of composite membrane for pervaporation has been developed. These membranes were prepared by free‐radical copolymerization of acrylic acid with a macromolecular polyfunctional crosslinker (allylhydroxyethylcellulose) inside the porous polyethylene (PE) film. It was shown that the porous structure of the PE matrix is filled with poly(acrylic acid) (PAA), and a layer of acid is formed on the film surface. To investigate the effect of the porous matrix on the composite membrane properties, a hydrogel membrane of crosslinked PAA was also prepared without the matrix using the same procedure. PAA in both membranes was in the neutralized form (K⁺). Swelling behavior of the membranes and their separation characteristics for pervaporation were investigated in water–ethanol solutions depending on the ethanol concentration. All membranes exhibited a high degree of equilibrium swelling (Q = 20–50 g/g) in dilute ethanol solutions (0–30 vol %), and Q sharply dropped to 1.5–2 g/g at a EtOH concentration of 30–40 vol % due to collapse of the gel. All membranes under study were highly permeable and selective to water over a wide range of ethanol concentrations in the feed (50–96 vol %), but composite membranes had a higher separation factor due to the restriction effect of the matrix porous structure on swelling of PAA(K⁺) inside the pores. However, composite membranes were characterized by a lower permeation rate, compared to the crosslinked PAA membranes without a matrix, because of their lower effective surface for diffusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1461–1465, 2004     

Separation of oil/water emulsions using nano MgO anchored hybrid ultrafiltration membranes for environmental abatement

This work focuses on utilizing the dual role of sulfonated polyphenyl sulfone (SPPSU) as both an anchoring agent and an interlayer modifying agent in the preparation of nano MgO/SPPSU/PPSU membranes for oil removal from water. These asymmetric membranes were prepared using the phase inversion technique. The dispersed nano MgO was observed in the membrane matrix as seen by scanning electron microscope and energy dispersive X‐ray analysis. The reduction in contact angle value establishes the increases in hydrophilicity. An increase in SPPSU (wt %) loosens the nano MgO/SPPSU/PPSU membrane packing as exhibited by the increase of d‐spacing by X‐ray diffraction analysis. The antifouling properties were tested using humic acid, as a model foulant. Further, in castor oil/water emulsion separation, it was found that the membrane with 25 wt % anchored moiety SPPSU/nano MgO produced a greater flux recovery ratio of 94.9% (±0.3) without compromising the oil rejection of 99% (±0.4) and better oleophobic surfaces for oil. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42848.     

Formation,morphology and control of high-performance biomedical polyurethane porous membranes by water micro-droplet induced phase inversion

Biomedical polyurethane (BPU) porous membranes with controlled morphology and excellent permeability and mechanical properties were prepared via a method involving a phase inversion induced by water micro-droplets, which were generated by an ultrasonic atomizer. The cross-section morphology, air permeability and mechanical properties of the porous membranes were investigated. The SEM images demonstrated that the adjacent pores were connected by a micro-hole, serving as a “backdoor” for the pore. An interconnected porous structure was obtained, improving the air permeability of the BPU membrane relative to the membrane produced by immersion precipitation. Our studies indicated that the diameter of the pores in the membrane depended on the solution viscosity, allowing porous membranes with a desired morphology to be obtained by adjusting the polymer concentration and solution viscosity. The application of micro-droplets of water during membrane preparation reduced the exchange rate between the solvent and nonsolvent, resulting in the microphase separation of polymer molecules and the formation of a uniform porous structure in the membrane, which improved the air permeability and mechanical properties of the BPU porous membranes. This is a simple and effective preparation method for high-performance porous membranes with potential applications in tissue engineering scaffolds, controlled-release drug delivery and vascular grafts.     

Pore structure and properties of poly(ether ether ketone) hollow fiber membranes: influence of solvent‐induced crystallization during extraction

Poly(ether ether ketone) (PEEK) hollow fiber membranes were prepared by a thermally induced phase separation method with polyetherimide as diluent, and N‐methyl pyrrolidone (NMP), dichloromethane and a composite extractant composed of NMP, ethanolamine and water as extractant. The effects of the different solvents induced crystallization on the pore structure during extraction and the properties of the PEEK hollow fiber membranes were investigated in detail. The crystallization behaviors of the membranes were characterized by DSC and XRD. The effect of the extractants on the microscopic morphologies, pore structures, water fluxes and mechanical properties of the membranes were investigated. The results showed that the extraction ability of the composite extractant was the most significant, followed by NMP and dichloromethane. The crystallinity of the hollow fiber was 39.0% before extraction and was elevated to 39.2% after the extraction with NMP, 46.6% with dichloromethane and 46.7% with the composite extractant, which shows that dichloromethane and the composite extractant have strong ability to induce the crystallization of PEEK. The inner and outer surfaces of the membranes obtained after extraction by the composite extractant had the largest pore size and the highest surface porosity. The most probable pore diameter of the membranes obtained after extraction by NMP, dichloromethane and the composite extractant was 23.26 nm, 24.43 nm and 24.43 nm, respectively, which indicated that solvent‐induced crystallization was beneficial for the formation of larger pores. The pure water flux of the PEEK membrane prepared by the composite extractant was the largest, but the tensile strength was the lowest. © 2019 Society of Chemical Industry     

Preparation of porous poly(D,L‐lactide) and poly(D,L‐lactide‐co‐glycolide) membranes by a phase inversion process and investigation of their morphological changes as cell culture scaffolds

Porous membranes composed of the biodegradable polyesters poly(D,L ‐lactide) (PLA) and poly(D,L ‐lactide‐co‐glycolide) (PLGA) were prepared by a phase inversion process. The molecular weights of the polymers and the concentrations of the polymer solutions affected the pore size and structure of the PLA and PLGA membranes. The molecular weights and morphological changes of the membranes as a function of time were investigated under incubation at 37°C in a humidified 5% CO₂ atmosphere. The pores that formed in the membranes changed dramatically with increasing time under these conditions. From the thermal characterization of the polymers in their dry and wet states, we found that the glass‐transition temperatures of PLA and PLGA affected morphological structure changes in the porous membranes. We also prepared a collagen‐coated membrane to improve the interaction between the cell and the substrate, and we observed that the collagen coating enhanced the attachment and growth of Chinese hamster ovary cells on the substrate. Finally, we found that only PLA was a suitable material to prepare a porous membrane scaffold with the phase inversion process with PLA, and a collagen coating was necessary for cell culture on the membrane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2082–2092, 2004     

Development of a high-performance polysulfone hybrid ultrafiltration membrane using hydrophilic polymer-functionalized mesoporous SBA − 15 as filler

A novel polysulfone hybrid ultrafiltration membrane was developed by blending hydrophilic poly[poly(ethylene glycol) methyl ether methacrylate] [P(PEGMA)] grafted mesoporous SBA-15 [SBA-g-P(PEGMA)] as filler. The hydrophilic SBA-g-P(PEGMA) fillers were synthesized via surface-initiated atom transfer radical polymerization. The effects of the SBA-g-P(PEGMA) fillers on the prepared hybrid membranes were systematically investigated. Compared with pristine SBA-15 fillers, SBA-g-P(PEGMA) fillers contributed to higher hydrophilicity and a more developed pore structure in the hybrid membranes. Specifically, SBA-15 grafted with a moderate P(PEGMA) molecular weight could better preserve the valid open-ended filler pore structure in the membrane matrix, thus facilitating membrane permeability. The pure water flux of the as-prepared polysulfone (PSF)/SBA-g-P(PEGMA) membrane was three times that of the PSF/SBA-15 membrane (271.7 L m⁻² h⁻¹ vs. 88.2 L m⁻² h⁻¹) with similar membrane selectivity. Moreover, the PSF/SBA-g-P(PEGMA) membranes showed improved antifouling property. This work paves the way for developing high-performance hybrid membranes by blending of hydrophilic polymer-functionalized mesoporous fillers in the future. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47353.     

Green synthesis of porous polyvinyl alcohol membranes functionalized with l-arginine and their application in the removal of 4-nitrophenol from aqueous solution

Green and single-step synthesis of porous poly(vinyl alcohol) membrane functionalized with l -arginine (PVA-g-Arg) is presented. Crosslinking, l -arginine functionalization and pore forming occurred simultaneously by a thermally induced process without using a crosslinker or an initiator. As-synthesized PVA-g-Arg membranes possessed a porous structure with an average pore size of 32–56 μm depending on the amount of l -arginine. The PVA-g-Arg were utilized as adsorbent membranes for the removal of 4-nitrophenol (4-NP) from aqueous solutions and demonstrated higher adsorption capacity than that of the unmodified PVA porous membrane. The pseudo-second-order described satisfactorily the kinetic adsorption of 4-NP by the membranes while the isotherms followed both the Langmuir and Freundlich models. The negative values of ΔG° and thermodynamic parameters confirmed that the adsorption of 4-NP by the PVA-g-Arg membranes was spontaneous and exothermic. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47835.     

Thermo‐Responsive Membranes with Cross‐linked Poly(N‐Isopropyl‐acrylamide) Hydrogels inside Porous Substrates

Thermo‐responsive membranes were prepared by fabricating cross‐linked poly(N‐isopropylacrylamide) (PNIPAM) hydrogels inside the pores of porous Nylon‐6 (N6) membranes by the free radical polymerization method. SEM micrographs of the prepared membranes showed that PNIPAM hydrogels were filled uniformly throughout the entire thickness of the porous N6 membranes. Both PNIPAM‐filled N6 membranes prepared at 60 °C and at 25 °C exhibited significant reversible and reproducible thermo‐responsive diffusional permeability. When the environmental temperature remained constant, the diffusional coefficient of vitamin B₁₂ (VB₁₂) across the PNIPAM‐filled N6 membrane prepared at 25 °C was ca. twice the value of that prepared at 60 °C due to different filling yields. The thermo‐response factor of the membrane prepared at 25 °C was higher than that prepared at 60 °C. The 3‐dimensional interpenetrating network structure of the cross‐linked PNIPAM hydrogels inside the N6 porous substrates could effectively ensure a repeatable thermo‐responsive permeation performance.     

Development of polyethersulfone phase‐inversion membranes for membrane distillation using oleophobic coatings

Highly porous macrovoid‐free polyethersulfone membranes have been prepared using the phase‐inversion process with water as the non‐solvent. These membranes are of great interest for membrane distillation (MD) after application of a hydrophobic/oleophobic coating. The membrane structure was controlled by optimizing the process conditions and dope composition. Counter intuitively, increasing the polymer concentration favors the formation of larger surface pores under similar process conditions. A symmetric membrane is obtained when a sufficient amount of high‐molecular‐weight polyvinylpyrrolidone was added to the dope solution, which appears to play an important role in the structure formation process. The final membrane shows similar performance compared to commercial MD membranes. However, the membranes developed in this study show an oleophobic character, broadening the applications of MD. Moreover, the compressibility of these membranes is severely reduced compared to stretched membranes, which is expected to result in an improved MD performance at full scale. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45516.     

Preparation of porous silicon rubber membranes by breath figure method

A series of porous silicon rubber membranes with regularity and uniform size had been prepared by breath figure method form polydimethylsiloxane and hydrogen silicon oil (Si-H1341). Hydrophilicity and hydrophobicity of polymer, different methods of cast films, co-solvents, solid particle dispersants, temperature, solution concentration, and molecular weight of silicon rubber are considered and discussed in the article to analyze effects of experiment situations on porosity of porous silicon rubber membranes. Remarkably, using the method of blending silicon rubber with branch hydrophilic silica-gel, large area hydrophilic modification of the silicon rubber can be achieved, and it is easy to form pores with regular structure. With synergies of co-solvents, the excellent porosity with more rounded pore shape and better regularity is acquired. The results indicate that the pore size of the silicon were affected greatly by the addition of co-solvent, the boiling point of solvent, molecular weight of raw materials, and reaction temperature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47912.     

Gating Characteristics of Thermo‐Responsive Membranes with Grafted Linear and Crosslinked Poly(N‐isopropylacrylamide) Gates

Thermo‐responsive porous membranes with grafted linear and crosslinked poly(N‐isopropylacrylamide) (PNIPAM) gates are successfully prepared at temperatures above and below the lower critical solution temperature (LCST) of PNIPAM by using a plasma‐induced grafting polymerization method, and the effects of operation pressure and grafting temperature on the thermo‐responsive gating characteristics of the prepared membranes are investigated systematically. The fluxes of water through the grafted membranes increase simply with increasing the operation pressure no matter whether the environmental temperature is 40 °C or 25 °C. Under high operation pressure (e.g., higher than 0.14 MPa), the grafted linear PNIPAM gates deform to a certain extent, whereas the grafted crosslinked PNIPAM gates do not deform. For both membranes with grafted linear and crosslinked PNIPAM gates, the membranes prepared at 25 °C (below the LCST of PNIPAM) show larger thermo‐responsive gating coefficients than those prepared at 40 °C (above the LCST of PNIPAM), which results from different distributions of grafted PNIPAM gates in the membrane pores. When the PNIPAM gates are grafted at 25 °C, the grafted layer near the membrane surface is much thicker than that inside the membrane pores; on the other hand, when the PNIPAM gates are grafted at 40 °C, the grafted layer is homogeneously formed throughout the whole pore length. Both linear and crosslinked grafted PNIPAM gates in the membrane pores exhibit stable and repeatable thermo‐responsive “open‐close” switch performances under the operation pressure of 0.26 MPa. The results in this study provide valuable guidance for designing, fabricating, and operating thermo‐responsive gating membranes with desirable performances.     

MOF-801 polycrystalline membrane with sub-10 nm polymeric assembly layer for ion sieving and flow battery storage

Molecular sieving metal–organic framework (MOF) polycrystalline membranes have great potential for ion sieving and are desirable as efficient separators for devices of energy storage such as flow battery. Herein, we report a continuous MOF-801 polycrystalline membrane with an ultrathin polymeric assembly layer (less than 10 nm) for the vanadium flow battery (VFB). Owing to the precise sub-nanometer sieving pores and abundant H-bond networks in MOF-801 frameworks, the membrane exhibited better H/V selectivity (up to 194) and conductivity (about 0.028 S/cm) than commercial Nafion-117 membrane (H/V selectivity: ~9.5, conductivity: 0.017 S/cm). VFB results revealed that a cell with above MOF polycrystalline membrane showed high coulombic efficiency (CE: 96.1%) and excellent energy efficiency (EE: 83.2%) at 20 mA/cm², which was much comparable to Nafion membrane. This work demonstrates that MOF polycrystalline membrane is a promising candidate as ion sieving membrane for energy technique.     

Structural manipulation of PES constituents to prepare advanced alternative polymer for ultrafiltration membrane

Polyethersulfone (PES) is the most well-known polymer for the preparation of ultrafiltration (UF) membrane, but its membrane suffers from fouling. In this study, two engineered polymers were synthesized to provide optimal antifouling properties for UF membranes that simultaneously benefit from good properties of polyamide and PES. The choice of polyamide is due to its prominent characteristics and the convenience of its synthesis with various functional groups in a cost-effective way. Two hydroxyl containing polyamide bearing sulfone groups (PAS) and ether group (PAE) were synthesized by polycondensation method. The UF membranes were fabricated using the phase inversion method via immersion precipitation of PAS, PAE, and PES in dimethylacetamide, as a solvent and water, as a nonsolvent. The obtained membranes were compared and characterized by means of atomic force microscopy, scanning electron microscopy, contact angle, and Fourier transform infrared spectroscopy in the attenuated total reflection mode. The performance of membranes illustrated that the PAS and PAE membranes in comparison with the PES membrane had better porosity, water permeability, lesser protein fouling, more vertically finger-like pores, and more hydrophilic surface. The water permeability of PES, PAE, and PAS was 7.3, 64.0, and 78.0 L m⁻² h⁻¹ while their flux recovery ratio was 59.4, 83.3, and 86.7%, respectively. The promising permeability and antifouling properties of the PAS are potentially applicable in the efficient industrial separation and wastewater treatment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48690.     

Hierarchical structure control of MgAl2O4 porous ceramics and application to organic polymer filtration membrane

Asymmetric porous ceramic membranes typically have a very thin top layer with finer pores covered on thick porous layers with micrometer-scale pores. In this study, triple-layer asymmetric MgAl₂O₄ filtration membranes composed of (i) an Al₂O₃ support layer (circular pellet with ~10 µm pores) prepared by dry pressing, (ii) a reactively sintered MgAl₂O₄ intermediate layer (~40 µm in thickness), prepared by dip-coating with tackifier (PEG-20000), and (iii) another reactively sintered finer MgAl₂O₄ membrane layer (~20 µm in thickness), prepared by dip-coating without tackifier. Different from our previous studies for the microfiltration of submicrometer-sized particles, in this study we have challenged the ultrafiltration of water-soluble polymer molecules. Their filtration performance was investigated by removing 1 million molecular-weight polyethylene oxide (PEO) from water. The rejection rate of the triple-layer asymmetric filtration membrane to PEO was ~14%. The all-ceramic membrane in this study showed a comparable rejection rate with the reported inorganic–organic membrane, and it must be promising for excellent chemical and thermal stabilities as well as long durability.     

Morphology of microporous neosepta ion-exchange membranes and its effect on separation of biological mixtures

Specially prepared microporous Neosepta ion-exchange membranes were investigated to establish a correlation between their structural characteristics (pore-size distribution, porosity) and permeability to components of immunoglobulin (Ig) fractions of mouse ascitic fluids. The solutions to be separated contained IgG₁ with specificity to horseradish peroxidase or to the heavy chain of human IgM, some other proteins, and a large amount of ammonium sulfate (0.22–0.35M). Analysis of the membrane morphology carried out by scanning electron microscopy and mercury porosimetry showed that the membranes possess a polymodal pore-size distribution. There are large open pores (400–600 and 200–300 nm in diameter) on the membrane surfaces, but the void volume of the membranes is a system of connected pores of smaller diameters (from 60–100 to 7–10 nm). The main part of the pores in the membranes displaying the best separation ability was 8–17 nm in diameter. It was found that highly porous charged membranes (relative porosity 58–60%) with low ion-exchange capacity (0.02–0.1 meq/g) made it possible to achieve the desired desalination degree of protein mixture (80–83%) within 5–7 h instead of 5 days needed in the traditional dialysis. Moreover, the amount of separated accompanying proteins reached 25–30% depending on membrane porosity and the quality of specific IgG₁ was considerably improved. © 1995 John Wiley & Sons, Inc.