Effects of casting solution composition on performance of poly(ether sulfone) membrane

Flat-type poly(ether sulfone) (PES) membranes for ultrafiltration were prepared by the traditional phase-inversion technique. The effects of the concentration of PES and the combination of two solvents, dichloromethane (DCM) and N-methyl-2-pyrrolidone (NMP), with differences in volatility and solvating power on membrane performance were examined in terms of pure water flux (PWF) and solute rejection (SR) against poly(ethylene glycol) (PEG, MW 20,000). Changing the thermodynamic quality of PES/NMP casting solution by combining DCM, a volatile and weak solvent, affected the PWF of the resulting membrane. The SR of PES/DCM–NMP membrane, however, was more likely dependent upon the effect of evaporating the volatile solvent from the casting solution/air interface rather than the effect of changing the thermodynamic quality of the casting solution. Combining DCM in PES/NMP casting solution transformed the fingerlike macrovoids of PES/NMP membrane prepared without DCM into the isolated macrovoids. PES/DCM–NMP membrane prepared with PVP, a water soluble poreforming agent, showed an increased PWF while maintaining SR of over 90%, even under the reduced feeding pressure of 1 kg/cm². It is necessary to measure molecular weight cutoff of membrane for demonstrating the potential of PVP for improving the membrane permeability without losing the selectivity.© 1996 John Wiley & Sons, Inc.     

Preparation and properties of polyimide solvent‐resistant nanofiltration membrane obtained by a two‐step method

This study investigated the preparation of polyimide solvent‐resistant nanofiltration membranes by a two‐step method (casting the membrane first and then crosslinking by the thermal imidization method). The influences of polymer concentration, thickness of membranes, temperature of the imidization, phase inversion time and thermal imidization procedure were studied. The membranes with the highest rejection rate of Fast Green FCF (molecular weight 808.86 g mol^?1) were prepared in the following conditions: polymer concentration 13 wt%, phase inversion time 1 h, membrane thickness 150 µm and thermal imidization procedure 200 °C for 2.5 h, 250 °C for 2 h and 300 °C for 2 h in a vacuum environment; the heating rate was 5 °C min^?1. The membrane was stable in most of the solvents tested and the fluxes of some common solvents were equal to or higher than a number of commercial solvent‐resistant nanofiltration membranes. A much higher rejection of dyes in water than in methanol was observed in the filtration experiments and a new way to explain it was developed. Copyright © 2011 Society of Chemical Industry     

Sulfonated poly(ether ether ketone)‐induced porous poly(ether sulfone) blend membranes for the separation of proteins and metal ions

Asymmetric ultrafiltration (UF) membranes were prepared by the blending of poly(ether sulfone) (PES) and sulfonated poly(ether ether ketone) (SPEEK) polymers with N,N′‐dimethylformamide solvent by the phase‐inversion method. SPEEK was selected as the hydrophilic polymer in a blend with different composition of PES and SPEEK. The solution‐cast PES/SPEEK blend membranes were homogeneous for all of the studied compositions from 100/0 to 60/40 wt % in a total of 17.5 wt % polymer and 82.5 wt % solvent. The presence of SPEEK beyond 40 wt % in the casting solution did not form membranes. The prepared membranes were characterized for their UF performances, such as pure water flux, water content, porosity, and membrane hydraulic resistance, and morphology and melting temperature. We estimated that the pure water flux of the PES/SPEEK blend membranes increased from 17.3 to 85.6 L m^?2 h^?1 when the concentration of SPEEK increased from 0 to 40 wt % in the casting solution. The membranes were also characterized their separation performance with proteins and metal‐ion solutions. The results indicate significant improvement in the performance characteristics of the blend membranes with the addition of SPEEK. In particular, the rejection of proteins and metal ions was marginally decreased, whereas the permeate flux was radically improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology and performance of poly(vinylidene fluoride) flat sheet membranes: Thermodynamic and kinetic aspects

In this study, poly(vinylidene fluoride) (PVDF) membranes were prepared using two different solvents with various polymer concentrations to investigate the predominant kinetic or thermodynamic aspects of membrane preparation in a phase separation process. For this purpose, dimethyl sulfoxide (DMSO) as a weak solvent and N‐2‐methylpyrrolidone (NMP) as a strong solvent were used with polymer concentrations between 8 and 15 wt %. Scanning electron microscopy and water content, contact angle, and pore size measurements were used to assess the factors affecting the physicochemical properties of the prepared membranes. The results showed that in the case of NMP, the membrane structure is mainly controlled by thermodynamic parameters, while when using DMSO, kinetic parameters are predominant. According to the results, the prepared PVDF‐based membranes with DMSO exhibited a relatively denser top layer and less permeation compared to the NMP/PVDF membranes. The difference between the viscosities of the casting solutions with equal polymer concentrations in DMSO and NMP was considered to be the main effective factor in solvent/nonsolvent exchange, resulting in denser top layers in the DMSO/PVDF membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46419.     

Enhancement of flux and solvent stability of Matrimid® thin‐film composite membranes for organic solvent nanofiltration

The development of high flux and solvent‐stable thin‐film composite (TFC) organic solvent nanofiltration (OSN) membranes was reported. A novel cross‐linked polyimide substrate, consisting of a thin skin layer with minimum solvent transport resistance and a sponge‐like sublayer structure that could withstand membrane compaction under high‐pressure was first fabricated. Then the solvent flux was significantly enhanced without compromising the solute rejection by the coupling effects of (1) the addition of triethylamine/camphorsulfonic acid into the monomer solution, and (2) the combined post‐treatments of glycerol/sodium dodecyl sulphate immersion and dimethyl sulfoxide (DMSO) filtration. Finally, the long‐term stability of the TFC membrane in aprotic solvents such as DMSO was improved by post‐crosslink thermal annealing. The novel TFC OSN membrane developed was found to have superior rejection to tetracycline (MW: 444 g/mol) but was very permeable to alcohols such as methanol (5.12 lm^?2h^?1bar^?1) and aprotic solvents such as dimethylformamide (3.92 lm^?2h^?1bar^?1) and DMSO (3.34 lm^?2h^?1bar^?1). © 2014 American Institute of Chemical Engineers AIChE J, 60: 3623–3633, 2014     

Synthesis of a novel sulfonated poly(amide‐imide) and its application in preparation of ultrafiltration PES membranes as a modifier

Sulfonated poly(amide‐imide) (SPAI) copolymer was synthesized, characterized, and blended into poly(ether sulfone) (PES)/dimethylacetamide casting solutions to prepare ultrafiltration membranes. Different weight ratios of the copolymer (0–10 wt %) were mixed in the PES casting solution. The analyses of contact angle and attenuated total reflection‐Fourier transform infrared spectra were used to study hydrophilicity and physicochemical properties of the membrane surface, respectively. The membranes were further characterized by scanning electron microscopy images, ultrafiltration performance, and fouling analyses. The outcomes showed that addition of the SPAI in the PES matrix improved considerably the membranes hydrophilicity. Moreover, with increasing SPAI concentration, the porosity, flux recovery ratio, and pure water permeability of the modified membranes were improved. The pure water flux was increased from 3.6 to 12.4 kg/m² h by increasing 2 wt % SPAI. The antifouling property of the modified PES membranes against bovine serum albumin, tested by a dead‐end filtration setup revealed that bovine serum albumin rejection of the obtained membrane was also enhanced and the antifouling properties of the blending membranes were improved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46477.     

Effect of Isomeric Propanols on the Performances of Polyethersulfone Nanofiltration Membranes

Abstract

In this work, polyethersulfone (PES) asymmetric nanofiltration (NF) membranes were prepared by immersion precipitation phase inversion process. The casting solution contained N-methyl-2-pyrrolidone (NMP) as solvent, 1-propanol and 2-propanol as nonsolvent additives, and polyvinylpyrrolidone (PVP) as pore former additive. Water was used as a coagulant. The effects of the PVP content in the casting solution and the exposed time on the performances of the NF membranes were investigated. It was found that with the increase of PVP content, the pure water flux (PWF) increased to the largest value and then decreased. The rejection to PEG 1000 always decreased. The largest value (1281.40 kg · m^?2 · h^?1 · MPa^?1) of PWF appeared when the content of 1-propanol was 9 wt.%. However, when 2-propanol was added in the casting solution, the largest value of PWF was only 678.37 kg · m^?2 · h^?1 · MPa^?1 (the content of 2-propanol was 7 wt.% and other preparing conditions were unchanged). The results meant that both PWF and rejection of the membranes with 1-propanol as additive were higher than that of 2-propanol as additive. The possible reason was discussed from the viewpoint of the difference of solubility of propanols to PES and PVP.     

Effect of polyethylene glycol molecular weights and concentrations on polyethersulfone hollow fiber ultrafiltration membranes

Polyethersulfone (PES) hollow‐fiber membranes were fabricated using poly(ethyleneglycol) (PEG) with different molecular weights (MW = PEG200, PEG600, PEG2000, PEG6000, and PEG10000) and poly(vinyl pyrrolidone) PVP40000 as additives and N‐methyl‐2‐pyrrolidone (NMP) as a solvent. Asymmetric hollow‐fiber membranes were spun by a wet phase‐inversion method from 25 wt % solids of 20 : 5 : 75 (weight ratio) PES/PEG/NMP or 18 : 7 : 75 of PES/(PEG600 + PVP40000)/NMP solutions, whereas both the bore fluid and the external coagulant were water. Effects of PEG molecular weights and PEG600 concentrations in the dope solution on separation properties, morphology, and mechanical properties of PES hollow‐fiber membranes were investigated. The membrane structures of PES hollow‐fiber membranes including cross section, external surface, and internal surface were characterized by scanning electron microscopy and the mechanical properties of PES hollow‐fiber membranes were discussed. Bovine serum albumin (BSA, MW 67,000), chicken egg albumin (CEA, MW 45,000), and lysozyme (MW 14,400) were used for the measurement of rejection. It was found that with an increase of PEG molecular weights from 200 to 10,000 in the dope solution, membrane structures were changed from double‐layer fingerlike structure to voids in the shape of spheres or ellipsoids; moreover, there were crack phenomena on the internal surfaces and external surfaces of PES hollow‐fiber membranes, pure water permeation fluxes increased from 22.0 to 64.0 L m^?2 h^?1 bar^?1, rejections of three protein for PES/PEG hollow‐fiber membranes were not significant, and changes in mechanical properties were decreased. Besides, with a decrease of PEG600 concentrations in the dope solution, permeation flux and elongation at break decreased, whereas the addition of PVP40000 in the dope solution resulted in more smooth surfaces (internal or external) of PES/(PEG600 + PVP40000) hollow‐fiber membranes than those of PES/PEG hollow‐fiber membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3398–3407, 2004     

Preparation and characterization of polysulfone–cyclodextrin composite nanofiltration membrane: Solvent effect

α-Cyclodextrin membranes were prepared by the phase inversion method using four types of casting solvents such as N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc), and dimethyl formamide (DMF) herein-after termed as α-CD-NMP, α-CD-DMSO, α-CD-DMAc, and α-CD-DMF, respectively. The membranes were characterized by IR, XRD, TGA-DTA, DSC, and SEM analysis and show that solvents like NMP, DMA, DMF give good uniform morphological membranes and are better than that of DMSO. Thermal decompositions of the pure polymer and composite membranes indicate different range of thermal degradation of the membrane. This study reveals that the casting solvents NMP, DMF, DMAC have nearly same significant effect on morphology and other properties of the membranes. This is explained in terms of demixing behavior of the polymer and the combined effect of solvent volatility and polymer–solvent interactions as estimated from Hansen solubility parameter. Solvent hydrophobicity also affects the performance of the membrane and can be determined in terms of water permeability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of hydroxyl‐terminated polybutadiene additives on the poly(ether sulfone) ultra‐filtration membranes

Hydroxyl‐terminated polybutadiene (HTPB) was blended into a poly(ether sulfone) (PES) casting solution used to prepare ultra‐filtration (UF) membranes via the phase inversion technique. The membranes were then characterized by contact angle (CA) measurements and UF experiments. The CA was increased with the addition of HTPB in the PES membrane and also by lowering the gelation bath temperature. It was observed that the CA was lower for membranes prepared with N‐methyl‐2‐pyrrolidinone (NMP) as the solvent than those using N,N‐dimethylacetamide (DMAc) as solvent. The flux values were higher for membranes made using a 4°C gelation bath when compared with the ambient temperature ((25 ± 1)°C) irrespective of the cast solvents, NMP or DMAc. The flux values were much higher and the solute separations were lower for the HTPB‐based PES membranes than for the pure PES membrane, when the membranes were cast with DMAc as a solvent. On the other hand, both flux and separation values were much lower for the HTPB‐based PES membranes than for the pure PES membrane, when the membranes were cast using NMP. Atomic force microscopy and scanning electron microscopy were used for morphological characterization and the correlation of topography/photography with the performance data was also examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2292–2303, 2006     

Characteristics and Performances of Blended Polyethersulfone and Carbon-Based Nanomaterial Membranes: Effect of Nanomaterial Types and Air Exposure

Polyethersulfone (PES) is a widely used polymeric material for ultrafiltration or nanofiltration membranes. To enhance membrane permeability, rejection, and antifouling performance, the effect of four different types of carbon-based nanomaterials and air exposures during PES/carbon-based nanomaterial membrane fabrication was evaluated. The carbon-based nanomaterials were pristine carbon nanotubes, oxidized CNTs (CNTs-O), pristine graphene nanoplatelets (GNPs-P), and oxidized graphene nanoplatelets (GNPs-O). The characteristics and performances of pure and blended membranes were investigated based on their permeability, porosity, morphology, and hydrophobicity. Longer air contact time during membrane preparation resulted in lower membrane permeability, hydrophobicity, and porosity. All fabricated membranes tended to have channelled sponge-like structure, and highest permeability was attributed to the PES/GNPs-O membrane.     

Significance of thermodynamics and rheological characteristics of dope solutions on the morphological evolution of polyethersulfone ultrafiltration membranes

Herein, the effect of solvent type and polymer concentration on the thermodynamic and viscoelastic properties, and performance of polyethersulfone (PES) ultrafiltration (UF) membranes are investigated. The morphology and mechanical properties of the membranes are examined too. Rheological measurements indicated that solidification and instantaneous demixing occurred fast for PES/N-methyl-2-pyrrolidone (NMP) dope solution. This resulted in a dense skin layer with a finger-like structure confirmed by the scanning electron microscopy images. In comparison, PES/dimethylformamide (DMF) exhibited a delayed solidification and demixing with a sponge-like structure. Rheological characteristics and ternary phase diagrams of two systems are examined to gain insights and make correlations with the morphology of resultant membranes. Performance analysis revealed that membranes derived from PES/NMP system exhibited both improved pure water flux and bovine serum albumin rejection suggesting the superiority of NMP compared to DMF as the solvent of choice for the preparation of PES UF membranes.     

Effects of coagulation bath temperature on performances of polyethersulfone membranes modified by nanosilver particles in situ reduction

In this work, an in situ reduction method was used to prepare nanosilver‐modified polyethersulfone (PES‐Ag) ultrafiltration membranes by mixing up the reducing agent ethylene glycol and the protective agent polyvinylpyrrolidone to reduce AgNO₃ in the casting solution. The effects of coagulation bath temperature (CBT) on the separation performances, antifouling property, tensile strength, and stability of the nanosilver particles were researched. The results indicated that when the PES‐Ag membranes were prepared in 40°C coagulation bath, the loss rate of nanosilver particles during preparation was minimum, only 18.5%. With the CBT increasing from 20 to 60°C, the water flux of the PES and PES‐Ag membranes increased, whereas the rejection rate decreased. The largest flux reached 471 L·m^?2·h^?1 for PES‐Ag membranes prepared at 60°C and the rejection was over 90%. The results of contact angle and flux recovery ratio showed that PES‐Ag membranes had better hydrophilicity and antifouling property. Furthermore, the PES‐Ag membranes could inhibit Escherichia coli from growing. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Silane‐Crosslinked Asymmetric Polythiosemicarbazide Membranes for Organic Solvent Nanofiltration

Crosslinked polythiosemicarbazide (PTSC) membranes with a positively charged surface are fabricated via a reaction with (3‐glycidyloxypropyl)trimethoxysilane. The integrally asymmetric ultrafiltration membranes discussed here can be easily prepared by water‐induced phase separation using a PTSC solution in dimethylsulfoxide (DMSO). The crosslinked PTSC membranes are stable in DMSO, N,N‐dimethylformamide, and tetrahydrofuran and they reject molecules of molecular weights (MW) above 1300 g mol^?1. The influence of the crosslinking agent on the surface charge, membrane solvent resistance, and membrane performance is discussed. The crosslinked asymmetric PTSC membranes totally reject Direct Red dye (MW 1373 g mol^?1), while the pristine PTSC membrane does not show any rejection for this dye. This finding suggests that an inorganic‐type‐network is formed during the crosslinking reaction, which tunes the pore size of the prepared membranes.     

Concentration of gelatin solution with polyethersulfone ultrafiltration membranes

In this work, polyethersulfone (PES) flat sheet ultrafiltration (UF) membranes were prepared by immersion precipitation phase inversion process with polyvinylpyrrolidone (PVP 30K) and acetone as additives. The best preparation condition for PES membranes with high water flux and rejection (to BSA) was decided. It was found that the optimal composition of the polymer casting solution was: 16 wt% (PES), 2 wt% (PVP 30K), and 1 wt% (acetone). Pure water flux of the membrane prepared at this condition reached to 373 L/m² h at 0.1 MPa, and the rejection to BSA was 91%. Compared with other reports, the rejection was slightly low but the flux of the PES membrane was high. When the membrane was used to concentrate gelatin solutions, the rejection value was over 75%. It was found that increasing the feed temperature and transmembrane pressure enhanced the permeation flux, but the rejection decreased slightly. However, increasing the cross-flow velocity of the feed solution simultaneously increased both the permeation flux and the rejection.     

Antifouling ultrafiltration membrane fabricated from poly (arylene ether ketone) bearing hydrophilic hydroxyl groups

A new kind of membrane formation polymer, cardo poly(arylene ether ketone) bearing hydrophilic hydroxyl groups (PEK‐OH) was synthesized from the biphenol monomer 2‐(2‐hydroxyethyl)‐3, 3‐bis (4‐hydroxyphenyl)‐isoindolin‐1‐one (PPH‐OH), and 4, 4′‐difluorodiphenylketone. PEK‐OH asymmetric ultrafiltration membranes were prepared using the immersion coagulation phase inversion method. The PEK‐OH membrane prepared using the optimized conditions exhibited a pure water flux of 516 ± 18 L·m^?2·h^?1 and a 99.1 ± 1.4% rejection of bovine serum albumin (BSA) at an operating pressure of 0.1 MPa. The contact angle of PEK‐OH membrane was 66.0 ± 2.4 lower than these of the PEK‐C membrane (87.0 ± 2.8°, prepared from polymer PEK‐C under the same membrane formation condition as PEK‐OH membrane) and the UE50 membrane (84.0 ± 1.6°, a commercial PES ultrafiltration membrane). The amount of BSA protein adsorbed to the PEK‐OH membrane under static condition was measured to be 3.12 μg·cm^?2, which was greatly lower than that of 88.71 μg·cm^?2 and 74.40 μg·cm^?2 for the PEK‐C and the UE50 ultrafiltration membranes, respectively. Under dynamic filtration of BSA experiments, the PEK‐OH ultrafiltration membrane showed a 78.3% water flux recovery ratio, while only a 39.7% for the PEK‐C membrane and 46.5% for UE50 membrane were detected in the first cycle. After three cycles of BSA and LYZ filtration, the flux recovery ratio of PEK‐OH ultrafiltration membrane changed to be stable at 75% and 73%, while that of PEK‐C and UE50 ultrafiltration membranes remained declining gradually. Thus, hydrophilic PEK‐OH improves antifouling membrane property. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42809.     

Hydrophilic goethite nanoparticle as a novel antifouling agent in fabrication of nanocomposite polyethersulfone membrane

The goethite nanoparticle was used as a multifunctional additive to fabricate antifouling polyethersulfone (PES) nanofiltration membranes. The goethite/PES membranes were synthesized via the phase inversion method. The scanning electron microscopy (SEM) photographs showed an increase in pore size and porosity of the prepared membranes with blending of the goethite. The static water contact angle measurements confirmed a hydrophilic modification of the prepared membranes. With increase in the goethite content from 0 to 0.1 wt %, the pure water flux increased up to 12.7 kg/m² h. However, the water permeability decreased using high amount of this nanoparticle. Evaluation of the nanofiltration performance was performed using the retention of Direct Red 16. It was observed that the goethite/PES membranes have higher dye removal capacity (99% rejection) than those obtained from the unfilled PES (89%) and the commercial CSM NE 4040 NF membrane (92%). In addition, the goethite/PES blend membranes showed good selectivity and antifouling properties during long‐term nanofiltration experiments with a protein solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43592.     

Micro‐ and ultrafiltration film membranes from poly(ether ether ketone) (PEEK)

Film membranes from the thermoplastic poly(ether ether ketone) (PEEK) have been extruded and tested for their microfiltration and ultrafiltration performance. High‐performance asymmetric membranes have been obtained by extruding polymer blends of PEEK, polysulphone, and a small molecule solvent mixture, and then by removing the polysulphone and solvent in a subsequent extraction step. The process for making ultrafiltration membranes differs from microfiltration membranes only in the relative blend components, and the temperature of the film pick‐up rolls. Processing parameters with important effects on the membrane performance have been identified. Microfiltration membranes are characterized by their pore‐size distributions and SEM, and ultrafiltration membranes by their rejection of bovine serum albumin, bubble point, and SEM. Composite membrane for nanofiltration utilizing the PEEK ultrafiltration membrane as a substrate performed similarly to a commercial membrane for the same purpose. This work details the best method for making PEEK film membranes published to date. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1146–1155, 1999     

Preparation and characterization of hydrophilic and antifouling poly(ether sulfone) ultrafiltration membranes modified with Zn–Al layered double hydroxides

Zn–Al layered double hydroxide (LDH)‐entrapped poly(ether sulfone) (PES) ultrafiltration membranes with four different weight percentages, 0.5, 1.0, 2.0, and 3.0%, were prepared by a phase‐inversion method. Characterization by scanning electron microscopy, atomic force microscopy and contact angle (CA), equilibrium water content, porosity, average pore size, mechanical strength, and ζ potential measurement were used to evaluate the morphological structure and physical and chemical properties of membranes. Static protein adsorption, filtration, and rejection experiments were conducted to study the antifouling properties, water permeability, and removal ability of the modified membranes. The results show that significant change occurred in the membrane morphology and that better hydrophilicity, water permeability, and antifouling ability were also achieved for the PES/LDH membranes when a proper amount of LDH was used. For example, the CA value decreased from 66.60 to 50.21°, and the pure water flux increased from 80.21 to 119.10 L m^?2 h^?1 bar^?1 when the LDH loading was increased from 0 to 2.0 wt %. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43988.     

Preparation of poly(ether sulfone) hollow fiber UF membrane for removal of NOM

In this study, a high performance poly(ether sulfone) (PES) hollow fiber ultrafiltration (UF) membrane has been prepared for removal of natural organic matter (NOM). The membrane was spun from a dope solution containing PES/poly (vinyl pyrrolidone) (PVP 40K)/N‐methyl‐2‐pyrrolidone (NMP) by using a wet‐spinning process. Characterization of the membrane in terms of pure water flux, molecule weight cut‐off (MWCO), and retention for a model humic acid (HA) were conducted, and the fouling resistance was analyzed. The experimental results showed that the membrane had a pure water permeability of 20 × 10^?5 L m^?2 h^?1 Pa^?1 and a nominal MWCO of 6000 Da. The results also showed that the membrane retention for humic acid was over 97% and both productivity and selectivity for HA increased with increasing feed velocity. The PES membrane in this study exhibited a much lower fouling tendency than the commercial polysulfone membrane. SEM images revealed that the membrane had an outer dense skin and a porous inner surface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 430–435, 2006