Effect of additives concentration on performance of cellulose acetate and polyethersulfone blend membranes

Asymmetric micro porous membranes have been prepared successfully from blending of cellulose acetate (CA) and polyethersulfone (PES) by the phase inversion method with N, N-dimethylformamide (DMF) as solvent. Two additives were selected in this study, including polyethylene glycol 600 (PEG 600) and polyvinylpyrrolidone (PVP). The effects of concentration of additives on CA/PES blend membrane performance and cross-section morphology were investigated in detail. CA/PES membranes were compared with CA/PES/PEG and CA/PES/PVP membranes in the performance such as pure water flux, membrane resistance, porosity and cross-section morphology. The resulting blend membranes were also carried out the rejection and permeate flux of Egg Albumin (EA) proteins with molecular weight of 45 Da. The membranes thus obtained with an additive concentration of 5 wt% of both PEG and PVP exhibited superior properties than the 80/20% blend composition of CA and PES membranes. The permeate flux of protein was increased from 44 to 134 lm² h with increase in concentrations of both PVP and PEG in 80/20% blend composition of CA and PES membranes. Cross-sectional images from scanning electron microscopy showed larger macropores in the bottom layer of the membranes with increasing additives content. Observations from scanning electron microscopy provided qualitative evidence for the trends obtained for permeability and porosity results.     

Effect of Additive Concentration on Cellulose Acetate Blend Membranes-Preparation,Characterization and Application Studies

Abstract

Ultrafiltration techniques have particular advantages for simultaneous purification, concentration, and fractionation of macromolecules. A comparative study is presented on novel ultrafiltration polymeric blend membranes based on cellulose acetate (CA) prepared in the absence and presence of polymeric additives such as polyethylene Glycol 200 (PEG) and polyvinylpyrrolidone (PVP) by phase inversion technique using N,N′-dimethylformamide (DMF) as solvent. Polymer blend composition, additive concentration and casting, and gelation conditions were standardized for the preparation of asymmetric membranes by pore statistics and morphology. These blend membranes were characterized for compaction in ultrafiltration experiments at 414 kPa pressure in order to attain steady state flux and is reached within 4–5 h. The pure water flux was measured at 345 kPa pressure. Membrane hydraulic resistance derived by measuring water flux at various transmembrane pressures and found to be inversely proportional to pure water flux. Water content is estimated by simple drying and weighing procedures and found proportional to pure water flux for all the membranes. The molecular weight cut-offs (MWCOs) of different membranes were determined with proteins of different molecular weights and found to vary from 20 to 69 kDa depending on the PEG 200 and PVP content in the blend in the casting solution. Skin surface porosity of the membranes was analyzed by scanning the samples at various magnifications. The characterized CA, CA/PEG200 and CA/PVP membranes were used for cadmium ion rejection studies at 345 kPa.     

Effects of Gelatin and Nano-ZnO on the Performance and Properties of Cellulose Acetate Water Membranes

Biodegradable cellulose acetate (CA) membranes were prepared via phase inversion induced by immersion precipitation method. Acetic acid and deionized water were used as solvent and non-solvent, respectively. The modifying effect of gelatin and zinc oxide (ZnO) nanoparticles additives was investigated on the membranes in terms of water flux, protein rejection percentage, and fouling ability during two hours of bovine serum albumin separation from aqueous solution. Specimens were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), tensile test, contact angle technique, and porosity measurement. The incorporation of gelatin and ZnO nanoparticles into the CA matrix increased the porosity coefficient and hydrophilicity. Moreover, gelatin improved the tensile properties of the membrane.     

Studies on Cellulose Acetate/Low Cyclic Dimmer Polysulfone Blend Ultrafiltration Membranes and their Applications

Abstract

Flat sheet ultrafiltration membranes from cellulose acetate (CA)/low cyclic dimer polysulfone (LCD PSf) were prepared by a phase inversion method. N, N′‐Dimethyl formamide and different molecular weight of polyethylene glycol (PEG 200, PEG 400, and PEG 600) were used as solvent and pore‐forming additive, respectively. The membranes were characterized in terms of pure water flux, water content, porosity, membrane hydraulic resistance, and morphology. The pure water flux was found to reach the highest value of 181.82 Lm^?2h^?1 at 5 wt.% PEG of 600 molecular weight and 10 wt.% LCD PSf content in the blended solution for membrane preparation. SEM micrographs indicated that the addition of PEG into the CA/LCD PSf solution changes the inner structure of the membrane. The influence of filtration time and applied pressure on membrane permeability was examined by copper/polyethylenimine complex rejection studies. With increase in filtration time, the rejection of the copper/polyethylenimine complex decreased and the results were discussed.     

Membrane Concentration and Separation of L-Aspartic Acid and L-Phenylalanine Derivatives in Organic Solvents

Abstract

The concentration and separation of the amino acids N-benzyloxycarbonyl L-aspartic acid and L-phenylalanine methyl ester hydrochloride in organic solvents have been investigated using reverse osmosis membranes of two types of cellulose acetate, a nanofiltration membrane of polyamide-polyphenylene sulfone (PA-PPSO) composite and a gas separation membrane of polyimide composite in a stirred batch cell. The organic solvents used included primary, secondary, and tertiary alcohols, an ester, and a ketone. There were significant variations in permeate flux, solute rejection, and membrane stability. Usually the rejection of both amino acids was similar; however, certain membrane-solvent combinations gave significantly different levels of rejection. The highest rejection of amino acids (～0.94) at the lowest pressure of 0.5 MPa was obtained with the PA-PPSO membrane using methanol as a solvent. The cellulose acetate membranes gave reasonable rejection and fluxes but the membrane stability was very poor. The performance of the polyimide composite membrane was good with ethanol but poor with other solvents. The PA-PPSO membrane with methanol as solvent appeared the most promising combination, and the separation performance according to concentration polarization was discussed.

     

Effect of polyvinylpyrrolidone molecular weights on morphology,oil/water separation,mechanical and thermal properties of polyetherimide/polyvinylpyrrolidone hollow fiber membranes

We prepared polyetherimide (PEI) hollow fiber membranes using polyvinylpyrrolidones (PVP) with different molecular weights (PVP 10,000, PVP 40,000, and PVP 1,300,000) as additives for oil/water separation. Asymmetric hollow fiber membranes were fabricated by wet phase inversion technique from 25 wt % or 30 wt % solids of 20 : 5 : 75 or 20 : 10 : 70 (weight ratio) PEI/PVP/N‐metyl‐2‐pyrrolidone (NMP) solutions and a 95 : 5 NMP/water solution was used as bore fluid to eliminate resistance on the internal surface. Effects of PVP molecular weights on morphology, oil‐surfactant‐water separation characteristics, mechanical, and thermal properties of PEI/PVP hollow fiber membranes were investigated. It was found that an increase in PVP molecular weight and percentage in PEI/PVP dope solution resulted in the membrane morphology change from the finger‐like structure to the spongy structure. Without sodium hypochlorite posttreatment, hollow fiber membranes with higher PVP molecular weights had a higher rejection but with a lower water flux. For oil‐surfactant‐water emulsion systems (1600 ppm surfactant of sodium dodecylbenzenesulfonate and 2500 ppm oil of n‐decane), experimental results illustrated that the rejection rates for surfactant, total organic carbon, and oil were 76.1 ≈ 79.8%, 91.0 ≈ 93.0%, and more than 99%, respectively. Based on the glass transition temperature values, PVP existed in hollow fiber membranes and resulted in the hydrophilicity of membranes. In addition, using NaOCl as a posttreatment agent for membranes showed a significant improvement in membrane permeability for PVP with a molecular weight of 1300 K, whereas the elongation at break of the treated hollow fiber membranes decreased significantly. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2220–2233, 1999     

Effects of PEG on Morphology and Permeation Properties of Polyethersulfone Membranes

Abstract

Flat sheet asymmetric polyethersulfone (PES) ultrafiltration (UF) membranes were prepared from a homogenous solution of PES via immersion precipitation in a water coagulation bath. The effect of the solvents (N-methyl-2-pyrrolidone (NMP) and N,N-dimethylformamide (DMF)) in preparation of the casting solution was studied. The effects of the molecular weight of polyethylene glycol (PEG) (400, 1500, and 6000 Da) on the morphology and the permeation properties of PES membranes were also investigated. Surface and cross-sectional morphology of the prepared membranes were studied by Scanning electron microscopy (SEM). The permeation performance of the prepared membranes was evaluated in terms of pure water flux (J_w), water content, porosity, hydraulic permeability, protein solution flux, and protein rejection. A solution of human serum albumin (HSA, Mw = 66,000 Da) was used as feed to study the permeation properties of the prepared membranes. Increasing molecular weight of PEG additives from 400 to 6000 Da enhances pure water permeation flux and HSA solution permeation flux while it reduces the protein rejection.     

Zirconia and titania composite membranes for liquid phase separation: preparation and characterization

Crack-free tubular TiO₂/ZrO₂ composite ceramic membranes on ZrO₂ supports have been successfully synthesized from colloidal titania sols by the sol-gel technique. The pore sizes of the prepared membrane were mainly controlled by the sol properties and the calcination conditions. The influence of different parameters such as additives and solvents on the hydrolysis and polycondensation properties of the sols was studied by DTA–TG and viscosity measurements. The TiO₂/ZrO₂ composite ceramic membranes were characterized by X-ray diffraction and scanning electron microscopy. Composite membrane permeability and rejection properties were also investigated. The results proved that the range of composite membrane flux and retention could be controlled by controlling the amount of polyethylene glycol (PEG). PEG in titania sol systems was suitable for use as an organic additive to fabricate crack-free composite membranes. The larger the amount of PEG added to the precursor solution, the larger the size and number of pores produced in the prepared membranes when the PEG was completely combusted during heat-treatment. By controlling the amount of PEG added to the precursor solution, TiO₂/ZrO₂ composite ceramic membranes with different pore sizes were prepared, which can be used in photocatalytic membrane reactors and applied in liquid–liquid or liquid–solid separation in future research.     

聚间苯二甲酰间苯二胺平板膜的制备及其性能研究

以聚间苯二甲酰间苯二胺（PMIA）为制膜原料,氯化锂（LiCl）、聚乙二醇（PEG-400）和聚乙烯吡咯烷酮（PVP）为添加剂,通过非溶剂诱导相转化法制备了PMIA平板膜,系统考察了聚合物浓度、添加剂种类和含量对PMIA膜结构和性能的影响。结果表明,聚合物浓度和LiCl含量增加,铸膜液黏度增大,导致膜孔径减小,纯水通量降低。而PEG含量的增加,使得聚合物链呈现舒展状态,膜孔径增大,纯水通量升高,亲水性增强。随着PVP含量的增加,膜的纯水通量先升高后降低,膜的亲水性变差。当PMIA的质量分数为9%,LiCl的质量分数为2.8%,PVP的质量分数为1.2%时,膜的纯水通量高达1421.55 L·m^-2·h^-1·bar^-1,对牛血清蛋白（BSA）的截留率为80%,展现出较高的渗透性,为制备高性能膜材料提供了新的思路。     

聚间苯二甲酰间苯二胺平板膜的制备及其性能研究

以聚间苯二甲酰间苯二胺（PMIA）为制膜原料,氯化锂（LiCl）、聚乙二醇（PEG-400）和聚乙烯吡咯烷酮（PVP）为添加剂,通过非溶剂诱导相转化法制备了PMIA平板膜,系统考察了聚合物浓度、添加剂种类和含量对PMIA膜结构和性能的影响。结果表明,聚合物浓度和LiCl含量增加,铸膜液黏度增大,导致膜孔径减小,纯水通量降低。而PEG含量的增加,使得聚合物链呈现舒展状态,膜孔径增大,纯水通量升高,亲水性增强。随着PVP含量的增加,膜的纯水通量先升高后降低,膜的亲水性变差。当PMIA的质量分数为9%,LiCl的质量分数为2.8%,PVP的质量分数为1.2%时,膜的纯水通量高达1421.55 L·m^-2·h^-1·bar^-1,对牛血清蛋白（BSA）的截留率为80%,展现出较高的渗透性,为制备高性能膜材料提供了新的思路。     

Studies on fouling by natural organic matter (NOM) on polysulfone membranes: Effect of polyethylene glycol (PEG)

Polysulfone membranes were prepared via phase inversion technique by using polyethylene glycol with molecular weights of 400, 1500 and 6000 Da as pore forming agent in dope formulation. The performance of membrane was characterized using humic acid and water sample taken from Sembrong River, Johor, Malaysia was used as natural organic matter sources. Membrane properties were also characterized in terms of mean pore radius, pure water flux, humic acid rejection and fouling resistance. The results indicated that the pure water flux and mean pore radius of membranes increased with the increase of PEG content. Fourier transform infrared spectroscopy results revealed the presence of hydrophilic component in PSf/PEG blend with the significant appearance of O–H peak at 3418.78 cm^− 1. Scanning electron microscopy analysis revealed the presence of finger-like structure for all membranes and the structure intensified as PEG content was increased. The results obtained from the fouling study indicated that the membrane with the lowest PEG content and molecular weight has an excellent performance in mitigating fouling.     

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

Membranes 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.     

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.     

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     

Synthesis,characterization, and anti-fouling properties of cellulose acetate/polyethylene glycol-grafted nanodiamond nanocomposite membranes for humic acid removal from contaminated water

Polyethylene glycol-grafted nanodiamond (ND-PEG) was synthesized from pristine detonation NDs and utilized to prepare novel cellulose acetate/polyethylene glycol-grafted nanodiamond(CA/ND-PEG)nanocomposite membranes. Due to unique thermal, mechanical, and antibacterial properties and very easy cleaning of fouled ND-embedded CA nanocomposite membranes, we tried to investigate the performance of CA/ND-PEG membrane for humic acid (HA) removal from contaminated water. Surface functionalization was confirmed by Fourier transform infrared spectroscopy and thermogravimetry analysis. Pristine and functionalized ND with different concentration was added in the casting solution containing CA. The prepared membranes were characterized using contact angle, mechanical strength, scanning electron microscopy (SEM), transmission electron microscopy, and permeation tests. SEM micrographs of the surface of the membranes depicted the increase in the number of pores by the addition of ND and especially ND-PEG into polymer matrix. The results indicated that the nanocomposite membrane with 0.5 wt% ND-PEG exhibited excellent hydrophilicity, mechanical properties, permeability, high rejection, high abrasion resistance, and good anti-fouling performance. The HA adsorption on the membrane surface decreased from 2.85 to 2.15 mg cm^?2 when the ND-PEG content increased from 0 to 0.5 wt%. Most importantly, the HA filtration experiments revealed that the incorporation of ND and especially ND-PEG particles reduced membrane irreversible fouling, dramatically. Meanwhile, the analysis of the fouling mechanism based on Hermia’s model revealed that cake formation is a prevailing mechanism for all membranes.     

Effects of coagulation bath temperature and polyvinylpyrrolidone content on flat sheet asymmetric polyethersulfone membranes

In this study, effects of coagulation bath temperature (CBT) and polyvinylpyrrolidone (PVP K15) concentration as a pore former hydrophilic additive on morphology and performance of asymmetric polyethersulfone (PES) membranes were investigated. The membranes were prepared from a PES/ethanol/NMP system via phase inversion induced by immersion precipitation in a water coagulation bath. The morphology of prepared membranes was studied by scanning electron microscopy (SEM), contact angle measurements, and mechanical property measurements. Permeation performance of the prepared membranes was studied by separation experiments using pure water and bovine serum albumin (BSA) solution as feed. The obtained results indicate that addition of PVP in the casting solution enhances pure water permeation flux and BSA solution permeation flux while reducing protein rejection. Increasing CBT results in macrovoid formation in the membrane structure and increases the membrane permeability and decreases the protein rejection. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Effect of poly(vinyl pyrrolidone) concentration and coagulation bath temperature on the morphology,permeability, and thermal stability of asymmetric cellulose acetate membranes

Cellulose acetate (CA) is widely used in membrane processes. In this study, CA (weight‐average molecular weight = 52,000) was mixed with poly(vinyl pyrrolidone) (PVP; weight‐average molecular weight = 15,000) as an additive in 1‐methyl‐2‐pyrrolidone as a solvent. The phase‐inversion method was used for the preparation of flat‐sheet membranes. The effects of PVP concentration and coagulation bath temperature (CBT) on the morphology, pure water permeation flux, and thermal stability of the prepared membranes were studied and are discussed in this article. The solute rejection of the developed CA membranes was quantified with an insulin protein solution. The results showed that an increase in the CBT levels from 0 to 23°C along with an increase in the PVP concentration in the cast film from 0 to 1.5 wt % resulted in an increase in the macrovoid formation in the membrane sublayer, an increase in the pure water flux (PWF), and a decrease in insulin rejection. Further increases in the PVP concentration from 1.5 to 3, 6, and 9 wt % resulted in gradual suppression of the macrovoid formation, a decrease in PWF, and an increase in insulin rejection. Higher PVP concentrations and lower CBT levels also appeared to result in higher glass‐transition temperatures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

PA/PEG交联共聚反渗透膜的制备及耐污染性能

以聚丙烯腈（PAN）超滤膜为基底,在均苯三甲酰氯（TMC）和间苯二胺（MPD）界面聚合反应过程中引入聚乙二醇（PEG）,制备聚酰胺（PA）/PEG反渗透复合膜。利用傅里叶红外光谱（FTIR）、X射线光电子能谱（XPS）、场发射扫描电镜（FE-SEM）和原子力显微镜（AFM）等对膜的结构和物化性质进行了表征。考察了PEG分子量、PEG加入量、热处理温度及时间对膜反渗透性能的影响,并系统考察了膜对十二烷基硫酸钠（SDS）、十二烷基三甲基溴化铵（DTAB）以及牛血清蛋白（BSA）三种不同荷电性典型污染物的耐受性能。实验结果表明,相比于未改性的PA反渗透膜,PEG交联共聚反渗透膜的盐截留率和通量恢复率均有所提高。其中PA/PEG1000-0.1膜渗透通量为3.96kg/(m²?h),NaCl表观截留率为97.5%,并且对于SDS、DTAB和BSA都表现出较高的耐污染性,其中,SDS污染清洗后膜的通量恢复率可达89.4%。     

Preparation and Characterization of Cellulose Acetate/Aminated Polysulfone Blend Ultrafiltration Membranes and their Application Studies

Abstract

Ultrafiltration membranes are largely being applied for heavy metal ion separations from aqueous streams. Cellulose acetate (CA) and aminated polysulfone (APSf) based membranes are prepared in the absence and presence of the polymeric additive, polyethylene glycol, PEG 600, in various compositions. The effects of polymer blend composition and additive concentration on compaction, pure water flux, membrane hydraulic resistance, water uptake, and contact angle has been investigated to evaluate the performance of the membranes and the results are discussed. Surface and cross-sectional morphologies of membranes were also analyzed using scanning electron microscopy. Toxic heavy metal ions such as Cu²⁺, Ni²⁺, Cd²⁺, and Zn²⁺ were separated by the blend membranes using polyethyleneimine (PEI) as polymeric ligand. The rejection and permeate flux efficiencies of the blend membranes are compared with pure cellulose acetate membranes.     

Preparation and characterization of asymmetric polyethersulfone nanofiltration membranes: The effects of polyvinylpyrrolidone molecular weights and concentrations

In this study, asymmetric flat‐sheet polyethersulfone (PES) nanofiltration (NF) membranes were prepared via immersion precipitation phase inversion with the addition of polyvinylpyrrolidone (PVP). The effects of PVP with the molecular weights (MW) from 17 to 1400 kDa and the concentration from 0 to 3.0 wt % on the morphologies and performances of PES membranes were systematically studied. The prepared membranes were characterized by SEM, AFM, ATR‐FTIR, contact angle, membrane porosity, the water flux, and the rejection measurement. The results indicated that the porosity and the hydrophilicity of PES NF membrane increased with increasing PVP concentration, and the hydrophilicity of PES NF membrane also improved with increasing PVP MW. The enhancements of the porosity and hydrophilicity resulted in the higher water flux of PES NF membrane. The rejection of Bordeaux S (MW 604.48 Da) for the prepared PES membrane was increased to above 90% with the low PVP concentration, but it turned to decrease remarkably when the PVP concentration reached to a critical value which related to PVP MW. It was concluded that the addition of a small amount of PVP could significantly increase the permeability of PES NF membrane and maintain its rejection of Bordeaux S above 90%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43769.