Rejection Of Polyethylene Glycol Research Articles

Enabling Solution Processable COFs through Suppression of Precipitation during Solvothermal Synthesis.

Covalent organic frameworks (COFs) are crystalline, nanoporous materials of interest for various applications, but current COF synthetic routes lead to insoluble aggregates which precludes processing for practical implementation. Here, we report a COF synthesis method that produces a stable, homogeneous suspension of crystalline COF nanoparticles that enables the preparation of COF monoliths, membranes, and films using conventional solution-processing techniques. Our approach involves the use of a polar solvent, diacid catalyst, and slow reagent mixing procedure at elevated temperatures which altogether enable access to crystalline COF nanoparticle suspension that does not aggregate or precipitate when kept at elevated temperatures. On cooling, the suspension undergoes a thermoreversible gelation transition to produce crystalline and highly porous COF materials. We further show that the modified synthesis approach is compatible with various COF chemistries, including both large- and small-pore imine COFs, hydrazone-linked COFs, and COFs with rhombic and hexagonal topologies, and in each case, we demonstrate that the final product has excellent crystallinity and porosity. The final materials contain both micro- and macropores, and the total porosity can be tuned through variation of sample annealing. Dynamic light scattering measurements reveal the presence of COF nanoparticles that grow with time at room temperature, transitioning from a homogeneous suspension to a gel. Finally, we prepare imine COF membranes and measure their rejection of polyethylene glycol (PEG) polymers and oligomers, and these measurements exhibit size-dependent rejection and adsorption of PEG solutes. This work demonstrates a versatile processing strategy to create crystalline and porous COF materials using solution-processing techniques and will greatly advance the development of COFs for various applications.

Development of Ultrafiltration Membrane from Polyethylene Terephthalate (Pet) Bottle Waste

Polyethylene Terephthalate (PET) bottle is used as beverage packaging, which is very convenient as one time use packaging. However, the huge amount of PET bottle waste has been becoming a serious problem for the environment. The utilization of PET bottle waste is very important to reduce the environmental problem. In this work, PET bottle waste was used a raw material to develop an ultrafiltration (UF) membrane. The membrane was prepared by using a phase inversion technique. The effect of the type of solvent, additive, and non-solvent on the microstructure and ultrafiltration performance of the membrane was studied. Different type of solvent, phenol, m-cresol, and DMSO were used to dissolve PET bottle as the source of membrane polymer. Two different additives, Polyethylene Glycol (PEG) and Polyvinyl Pyrrolidone (PVP) were used. Membrane 3 with the composition of PET, phenol as solvent, and PEG as additive was prepared successfully. The variation of aqueous alcohol solutions as non-solvent resulted in different microstructures of the membranes as shown by the scanning electron microscopy (SEM). The permeation experiment result using pure water as the feed showed that membrane 3 using aqueous butanol as non-solvent (membrane 3-ButOH) exhibited the highest permeate flux compared to that of membrane 3 using aqueous propanol (membrane 3-PrOH) or ethanol as non-solvent (membrane 3-EtOH). The ultrafiltration experiment was carried out using a feed solution of water containing polyethylene glycol (PEG) 20,000. The membrane 3-EtOH showed the lowest permeate flux of 3.24 kg/m h, but the highest rejection of PEG 20,000 of 65.87%. The membrane 3-PrOH had a permeate flux of 11.57 kg/m h and a rejection of 64.73%. Whereas the membrane 3-ButOH showed the highest permeate flux of 27.78 kg/m h, but the lowest rejection 16.93%. This result was obtained due to the different membrane microstructures which were strongly affected by the type of non-solvent.

Use of cellulose acetate/polyphenylsulfone derivatives to fabricate ultrafiltration hollow fiber membranes for the removal of arsenic from drinking water.

Cellulose acetate (CA) and cellulose acetate phthalate (CAP) were used as additives (1 wt%, 3 wt%, and 5 wt%) to prepare polyphenylsulfone (PPSU) hollow fiber membranes. Prepared hollow fiber membranes were characterized by surface morphology using scanning electron microscopy (SEM), surface roughness by atomic force microscopy (AFM), the surface charge of the membrane was analyzed by zeta potential measurement, hydrophilicity by contact angle measurement and the functional groups by fourier transform infrared spectroscopy (FTIR). Fouling resistant nature of the prepared hollow fiber membranes was evaluated by bovine serum albumin (BSA) and molecular weight cutoff was investigated using polyethylene glycol (PEG). By total organic carbon (TOC), the percentage rejection of PEG was found to be 14,489 Da. It was found that the hollow fiber membrane prepared by the addition of 5 wt% of CAP in PPSU confirmed increased arsenic removal from water as compared to hollow fiber membrane prepared by 5 wt% of CA in PPSU. The removal percentages of arsenic with CA-5 and CAP-5 hollow fiber membrane was 34% and 41% with arsenic removal permeability was 44.42 L/m2h bar and 40.11 L/m2h bar respectively. The increased pure water permeability for CA-5 and CAP-5 hollow fiber membrane was 61.47 L/m2h bar and 69.60 L/m2 h bar, respectively.

Cross-linked thin poly(vinyl alcohol) membrane supported on polysulfone in tea polyphenol separation

ABSTRACTCross-linked polymeric colloids are coated over porous polysulfone support by a simple method to prepare high-flux membrane for separation of tea polyphenols. The colloidal particles were prepared by electrostatic interaction and cross-linking between poly(vinyl alcohol) and maleic acid. The membrane exhibited >90% rejection of polyethylene glycol of 6000 Da molecular weight. The membranes exhibited flux of about 15–20 LMH with 70–90% polyphenol retention depending upon the coating and support types at 500 psi and had shown stability under continuous running of the separation experiments in water or methanol at pressurized condition.

The effect of carboxyl multiwalled carbon nanotubes content on the structure and performance of polysulfone membranes for oil sands process-affected water treatment

Abstract Ultrafiltration nanocomposite polysulfone (PSU) membranes containing 0 to 5 wt% carboxyl ( COOH) modified multiwalled carbon nanotubes (mMWNT) were fabricated and used to treat oil sands process-affected water (OSPW). Addition of mMWNT to PSU resulted in increased membrane surface hydrophilicity. Small additions of mMWNT (up to 1 wt%) resulted in decreased average pore size on the selective membrane surface. Pure water and OSPW flux followed the same trend, decreasing with small mMWNT additions (up to 0.5 wt%), followed by an increasing flux with higher mMWNT additions. All nanocomposite membranes had a higher rejection of polyethylene glycol (PEG) (76.5%–92.3%) than plain PSU membrane (65.5%). Membrane containing 2 wt% mMWNT had the highest PEG flux and PEG rejection of 83.1%. Addition of mMWNT reduced the tendency for membrane fouling to occur, indicated by a decrease in fouling ratios and increased flux recovery ratios for nanocomposite membranes as compared with those obtained for plain PSU. The dominant fouling mechanisms during OSPW filtration were standard blocking and cake filtration. Additions of 0.2 wt% and 2 wt% mMWNT resulted in permeates with SDI15 values lower than 1.0 and increased acid-extractable fraction removal (11.9% and 13.9%, respectively) as compared with AEF removal by plain PSU membrane.

Polyaniline Composite Membranes Synthesis in Presence of Various Acid Dopants for Pressure Filtration

Polyaniline is a conductive polymer that is recently used as a material in producing a pressure filtration membrane. Polyaniline can be doped in various acids as dopants of different sizes and shapes to modify its inherent properties to produce membrane with high flux and rejection. This work is aimed to fabricate polyaniline composite membrane in presence of different acids as dopants namely hydrochloric acid, maleic acid, poly(methyl vinylether) acid (PMVEA) and polyacrylic acid (PAA). This polyaniline was coated onto microporous polyvinylidene fluoride (PVDF) support by using a specially fabricated two compartment cell. The field emission scanning electron microscope (FESEM) results show that the morphology of the coated polyaniline on PVDF membrane support is in globular shapes, which elongates at different sizes depending to the acid used. From the thermal analysis, the melting point of polyaniline coated PVDF membrane remains at 260°C, similar as obtained in the pristine microporous PVDF indicating no thermal change upon polyaniline coating. From all membranes prepared, the doped polyaniline membrane possessed a good conductivity value except for polyaniline-PMVEA membrane, which has the lowest value. In terms of the membrane filtration performance, which was measured based on the flux of pure water and polyethylene glycol (PEG) rejection, polyaniline-PMVEA membrane has a high flux and the highest PEG rejection. This result indicates that the conductivity does not influence much on the membrane filtration performance, but rather due to the physical coating itself. Different acid dopants present during polyaniline coating will lead to different filtration performance.

An Experimental Investigation: Effect of Phase Inversion Methods on Membrane Structure and Its Performance on PEG Filtration

In this work, the effect of different phase inversion process on membrane morphology and performance was studied. Polyethersulfone (PES) based polymeric membranes was fabricated containing polyvinylpyrrolidone (PVP) and carboxylic functionalized multiwall carbon nanotubes (MWCNT) as additives and polyethylene glycol (PEG) having a molecular weight 1K, 10K and 35K (Dalton) were used as a model solution for observing the rejection/filteration ability of fabricated membranes. Non-solvent induce phase separation (NIP) and dry-wet phase separation (DWP) method was adopted for membrane synthesis. The FTIR spectra showed that PVP/MWCNT was effectively blended with PES polymer and different phase inversion method led to different internal morphologies of membranes as confirmed by FESEM images. The PEG rejection results suggested that membranes formed by DWP method had approximately double rejection ability than membranes formed by NIP process.

One-pot synthesis of supported hydrogel membranes via emulsion templating

Supported hydrogel membranes were produced by one-pot synthesis by polymerisation of suitable emulsion templates. High internal phase emulsions (HIPEs) with styrene (St), divinylbenzene (DVB) and ethylhexyl acrylate (EHA) in the continuous phase and methacrylic acid (MAA) in the internal phase were polymerised to prepare poly(MAA) hydrogel grafted poly(St-co-DVB-co-EHA) poly(merised)HIPEs. By changing the concentration of the crosslinker, N,N′-methylenebisacrylamide, in the internal phase of the emulsion template the crosslinking density of the grafted poly(MAA) was tuned. The presence of the hydrogel was indicated by a change in pore morphology, e.g. coverage of the pore throats and the wrinkled pore wall surface, and the increase in the density of the composite polyHIPEs as compared to control polyHIPEs. Moreover, the increase in foam density and reduction of porosity were related to the crosslinking degree of the hydrogel. The water uptake of the composite polyHIPEs exceeded the pore volume of the polyHIPE scaffold supporting the grafted hydrogel. The permeability and rejection of aqueous solutions of polyethylene glycol (PEG) by the hydrogel grafted polyHIPE membranes were strongly pH dependent, the permeability decreased and the rejection of PEG increased with increasing pH due to the increased swelling of the hydrogel. A 91% rejection of 50kDa PEG for polyHIPE supported hydrogel membranes has been identified, which qualifies such membranes for ultrafiltration applications.

Calcium alginate hydrogel filtration membrane with excellent anti-fouling property and controlled separation performance

Calcium alginate (CaAlg) hydrogel filtration membrane was prepared using polyethylene glycol (PEG) as the pore-forming agent. Ultrasonic time-domain reflectometry technology was employed to analyze the membrane-forming process. The CaAlg filtration membrane was characterized by SEM, FTIR, TG and DTG. The mechanical behavior of the membrane was also evaluated. Concentrations of sodium alginate (NaAlg) and PEG on the pure water flux (PWF) and filtration properties of lysozyme (Lyz) solutions were investigated. Results showed that the PWF increased with an increase in the pressure initially, and then reached a stable value. The CaAlg filtration membrane prepared with lower NaAlg concentration and higher PEG concentration had higher flux. CaAlg filtration membranes exhibited good anti-fouling properties. The rejection of PEG reached above 90% when the molecular weight (Mw) of PEG in feed solution was larger than the pore-forming agent PEG for preparing the membranes. The CaAlg filtration membrane prepared using PEG400 as the pore-forming agent could reject almost 100% Brilliant Blue G250 (Mw=854.02Da), and 99.5% Congo Red (Mw=696.68Da).

Effects of Additives on the Morphology and Performance of PPTA/PVDF in Situ Blend UF Membrane

Poly(p-phenylene terephtalamide) (PPTA), a high-performance polymer with high modulus and good hydrophilicity, is often used as a reinforced material. However, due to its high crystallity, micro-phase separation often occurs in the blends. In this paper, PPTA/poly(vinylidene fluoride) (PVDF) compatible blend solution was synthesized by in situ polycondensation. Blend ultra-filtration membrane was prepared through the immersion phase inversion process. In order to obtain desired pore structure, the effects of different additives including hydrophilic polymer (polyethylene glycol (PEG)), inorganic salt (lithium chloride (LiCl)) and the surfactant (Tween-80) on the morphology and performance of PPTA/PVDF blend membranes were studied. The membrane formation process was investigated through ternary phase diagram (thermodynamics) and viscosities (kinetics) analysis. It was found that, with the increasing of LiCl content, a porous membrane structure with long finger-like pores was formed due to the accelerated demixing process which resulted in the increase of porosity and pore diameter as well as the enhancement of water flux and the decline of PEG rejection. When Tween content increased to over 3 wt%, dynamic viscosity became the main factor resulting in a decreased phase separation rate. The transfer of PEG and LiCl molecules onto membrane surface increased the surface hydrophilicity. The effect of Tween content on membrane hydrophilicity was also correlated with the compatibility of blend components.

Fabrication of magnetic nanocomposite membrane for separation of organic contaminant from water

AbstractIn this work, separation of disperse dyes and polyethylene glycol (PEG) as organic contaminant by nanocomposite membrane was investigated. The main goal of this study is to achieve more efficient separation of contaminant from water at high fluxes. For this purpose, iron oxide nanoparticles (NP) were synthesized through co-precipitation, blended with polysulfone/N-methylpyrrolidone solution, and finally, dispersed in membrane structure after coagulation of casted polymeric solution. Effect of magnetic nanoparticle concentration on membrane structure and filtration performance was studied. According to filtration experiments, the increasing of nanoparticle concentration in membrane matrix cause permission flux to raise. On the other side, any increases in magnetic nanoparticle content improved disperse dyes and PEG rejection as organic contaminant. Iron oxide NP in polymeric solution act as an agent to increase viscosity and cause a delay in phase inversion, decrement in membrane pore size, and fin...

The effect of polymer concentration and additives of cast solution on performance of polyethersulfone/sulfonated polysulfone blend nanofiltration membranes

The effect of polymer concentration of polyethersulfone (PES) plus sulfonated polysulfone (SPSF) and additives of cast solution on performance of PES/SPSF blend nanofiltration (NF) membranes was investigated. The field emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze characteristic of PES/SPSF blend NF membranes. The water flux of PES/SPSF blend membranes decreased dramatically with an increase in polymer concentration of PES plus SPSF. The rejection of polyethylene glycol (PEG) and salts increased with increasing polymer concentration of PES plus SPSF. When acetone was used as an additive, the water flux declined with increasing mass concentration of acetone, but the rejection of PEGs and salts increased. The PES/SPSF blend NF membranes with mimimum rejection of sodium chloride indicated that it could separate monovalent salts from multivalent salts effectively, which would be potential application in softening water for drinking water resource.

Dehydration and pore swelling effects on the transfer of PEG through NF membranes

In order to investigate the significance of "salting-out" and "pore swelling" effects on the nanofiltration of neutral solutes, rejection properties of two NF ceramic and polymeric membranes were studied with single polyethyleneglycol (PEG) solution and mixed PEG/inorganic electrolyte solutions. For both membranes, the rejection rate of PEG was found to decrease significantly in the presence of ions. In the case of the ceramic membrane (rigid pores), this phenomenon was imputed to the sole partial dehydration of PEG molecules induced by the surrounding ions. This assumption was confirmed by the lowering of the PEG rejection rates which followed the Hofmeister series. Experimental data were used to compute the resulting decrease in the Stokes radius of PEG molecules in the presence of the various salts. Concerning the polymeric membrane, the decrease in the rejection rate was found to be systematically higher than for the ceramic membrane. The additional decrease was then ascribed to the swelling of the pores. The experimental data of rejection rates were then used to compute the variation in the mean pore radius in the presence of the various salts. The pore swelling phenomenon due to accumulation of counterions inside pores was supported by electrokinetic charge density measurements.

Desalination of dye utilizing copoly(phthalazinone biphenyl ether sulfone) ultrafiltration membrane with low molecular weight cut-off

Copoly(phthalazinone biphenyl ether sulfone) (PPBES) ultrafiltration (UF) membrane with low molecular weight cut-off (MWCO) possesses excellent thermal resistance and it is suitable to be utilized in dye wastewater treatment at high temperature. The rejection of polyethylene glycol (PEG1000) of the membrane was 100% while the flux was 232 L/m 2 h at 20 °C and 0.2 MPa. It was showed that the rejections of NaCl and Na 2SO 4 were both 0%. The rejections of Congo Red (Direct Dye), Sulfur Black B (Sulfur Dye) and Gentian Violet (Anionic Dye) were all 100% while the rejections of C. I. Reactive Yellow 86 (Reactive Dye), C. I. Disperse Red 73 (Disperse Dye) and Acid Chrome Blue K (Cationic Dye) were 79%, 54% and 43%, respectively. The fluxes of the membrane during treatment were all higher than 87 L/m 2 h at 20 °C and 0.2 MPa except for C. I. Disperse Red 73. Effect of inorganic salt concentration on membrane performance was investigated. Thermal resistance of the membrane was also evaluated with Sulfur Black B. It was found that the flux increased 4.5 times while the rejection did not decline when the operation temperature was raised from 20 °C to 95 °C. The membrane ran 20 h at 90 °C without the membrane performance decline which showed that the membrane had good thermal resistance.

Influence of salts on the rejection of polyethyleneglycol by an NF organic membrane: Pore swelling and salting-out effects

Rejection rate measurements were carried out with a single polyethyleneglycol (PEG) solution and mixed PEG/inorganic salt solutions for a nanofiltration polyamide membrane. It was observed that PEG rejection is significantly lower in mixed-solute solutions, i.e. when a salt is present (KCl, LiCl, MgCl 2 and K 2SO 4), and that rejection rate drop increases with salt concentration. Similar nanofiltration experiments were conducted with an NF ceramic membrane in previous works. The rejection of PEGs was also found to decrease in the presence of salts and this phenomenon was imputed to the partial dehydration of PEG molecules by surrounding ions (salting-out effect). Unlike results obtained with the ceramic membrane, the lowering of PEG rejection rates observed with the organic membrane does not follow the Hofmeister series. It means that the salting-out effect cannot solely explain the rejection lowering found for the organic membrane. The additional hypothesis which was considered in the present work is that the rejection lowering might be caused by an increase in the effective pore size (pore swelling) due to accumulation of counterions inside pores resulting from an increase in the surface charge density in the presence of ions. In order to evaluate the significance of the pore swelling phenomenon, the experimental data of rejection rates obtained with the organic membrane were used to compute the variation in the mean pore radius in the presence of the various salts (the Stokes radii of PEG molecules in the presence of the various salts having been determined previously from rejection rates obtained with the ceramic membrane). It was shown that the effective pore size depends on the salt nature and increases with salt concentration. The hypothesis of pore swelling was supported by electrokinetics charge density data calculated from tangential streaming potential measurements: the more the membrane surface charge density increases, the higher the effective average pore size becomes. Finally, the contribution of pore swelling and salting-out to the overall decrease in the rejection rate of PEG was evaluated.

Effect of salts on the retention of polyethyleneglycol by a nanofiltration ceramic membrane

Retention properties of a nanofiltration ceramic membrane were investigated with single polyethyleneglycol (PEG) solutions and mixed PEG/inorganic salt solutions. The rejection rate of PEGs was found to decrease in the presence of ions. It was shown that the effect of ions on the retention of neutral solutes increases with the salt concentration. This salt effect phenomenon is in accordance with former observations showing that the retention of uncharged solutes by nanofiltration organic membranes decreases in the presence of salts [J. Membr. Sci. 258 (2005) 123–132; J. Membr. Sci. 247 (2005) 11–20]. It has been postulated that the decrease in the rejection rate of neutral solutes could result (i) from pore swelling, i.e. the increase in the mean pore radius due to repulsion forces between counterions in the electrical double layer at the pore walls and/or (ii) from Hofmeister effects, that is a partial dehydration of neutral molecules in the presence of ions because water would preferentially solvate ions. Since the matrix of ceramic membranes is rigid, our findings show that Hofmeister effects are probably responsible for the observed decrease in the rejection rate of PEG molecules when salts are added in solution (of course it does not mean that pore swelling does not contribute to the lowering of neutral solute rejection rates observed with organic membranes in mixed-solute solutions). This assumption is confirmed by the lowering of the PEG rejection rates which follows the Hofmeister series, i.e. Mg 2+> Li +> K + and C 6H 5O 7 3−> SO 4 2−> Cl −. Experimental data were used to compute the resulting decrease in the Stokes radius of PEG molecules in the presence of the various salts.

Production and characterization of membranes of recycled waste materials: Cellulose acetate, obtained from sugarcane bagasse with polystyrene from plastics cups

AbstractMembranes of cellulose acetate from sugarcane bagasse (CA), as well as blends of this cellulose acetate and polystyrene from plastic cups (CA/PS) were produced by casting utilizing dichloromethane as solvent at the concentration 12% w/w. The membranes were characterized regarding ion diffusion by dialysis and properties of pure water permeation rate, PEG rejection (utilizing an aqueous solution 1% w/v of polyethylene glycol (PEG), 45 and 80 kDa). Thermal characterization by thermogravimetric analysis and differential scanning calorimetry were also performed. The morphology of the membranes' cross‐sections was evaluated by scanning electron microscopy. The experiment of ion diffusion by dialysis showed that the ion diffusion coefficient of CA membrane is comparable to that found in the literature for membranes of commercial cellulose triacetate, 8.47 × 10−8 cm2 s−1, while the ion diffusion coefficient of blends decreased as PS was added to the system. Regarding transport driven by pressure, CA membrane presented low rejection of PEG 80 kDa. These results showed that CA membrane could be used in a range of application comprehending the process of ultrafiltration or microfiltration. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.

Influence of inorganic electrolytes on the retention of polyethyleneglycol by a nanofiltration ceramic membrane

Retention properties of a nanofiltration ceramic membrane were investigated with single polyethyleneglycol (PEG) solutions and mixed PEG/inorganic electrolyte solutions. The rejection coefficient of PEGs was found to decrease in the presence of ions. It was shown that the effect of ions on the retention of neutral solutes increases with the electrolyte concentration. This phenomenon was ascribed to the partial dehydration of PEG molecules induced by the surrounding ions. This argument was confirmed by using various electrolytes (KCl, LiCl and MgCl 2). It was found that the lowering of the PEG rejection coefficients follows the Hofmeister series, i.e. Mg 2+ > Li + > K +. Experimental data were used to compute the resulting decrease in the Stokes radius of PEG molecules in the presence of the various electrolytes.

Zirconium-containing mesoporous silica Zr-MCM-48 for alkali resistant filtration membranes

Zirconium-containing mesoporous silica (Zr-MCM-48) membranes were synthesized on a porous alumina support from an aqueous solution containing tetraethylorthosilicate (TEOS), zirconium propoxide (ZrPr) and cetyltrimethylammonium bromide (C 16TAB). The Zr-MCM-48 membranes show high resistance in alkaline solutions at pH 9–12 although the structure of the pure silica MCM-48 membranes collapsed even at pH 10. Zirconium species is considered to present near the pore surface of MCM-48 because the reactivity of ZrPr with surfactant (C 16TAB) molecules is much higher than TEOS in the starting solution. Zr-MCM-48 shows more stable in alkaline solutions than Ti-containing MCM-48 (Ti-MCM-48). The gas permeation and permporometry measurements suggest that there are no large pinholes and cracks in the Zr-MCM-48 membranes. From permporometry the average pore size of the Zr-MCM-48 membrane is estimated to be 2.5 nm. The filtration of polyethylene glycol (PEG) in water shows that the membranes has molecular weight cutoff (MWCO) of about 3800 u. The corresponding molecular size is 2.3 nm. The sharp increase in the rejection of PEG with increase in molecular weight shows narrow pore size distribution of the membrane. These results show that Zr-MCM-48 membranes have great potential for nanofiltration and ultrafiltration with high performance.

Novel ultrafiltration membranes prepared from the new miscible blends of polysulfone with poly(1-vinylpyrrolidone-co-styrene) copolymers

Miscibility of polysulfone (PSf) with poly(1-vinylpyrrolidone-co-styrene) (P(VP-S)) copolymers containing various amount of 1-vinylpyrrolidone (VP) was explored. PSf and P(VP-S) copolymers formed miscible blends when copolymers have VP from 68 to 88 wt.% and beyond these critical limits to form immiscible blends. Membranes for the ultrafiltration process were prepared from PSf blends with P(VP-S) copolymers. The membranes prepared from the miscible blends of PSf and P(VP-S) exhibited higher water flux than the membranes prepared from PSf without any loss in solute rejection. The water flux of the membrane prepared from the PSf/P(VP-S)70/1-methyl-2-pyrrolidone (NMP)=13/9/78 casting solution was increased up to 18 l/(m 2 h bar) with 92% rejection of polyethyleneglycol (PEG) 20,000. However, the solute rejection examined with the membranes fabricated from the immiscible blends of PSf and P(VP-S) lower than that of PSf membranes. The morphologies of membranes were examined to rationalize the observed membrane performance. The cross-sectional morphology of membrane prepared from the miscible blend is similar to that of the PSf membrane but with a thick sponge-like skin layer while that of membrane prepared from the immiscible blend showed separated phase structure. The relatively large pore in the membrane prepared from the immiscible blend results in low solute rejection.