Surface characteristics and hemocompatibility of PAN/PVDF blend membranes

Polyacrylonitrile (PAN) was blended with polyvinylidine fluoride (PVDF) at various ratios and made into membranes. The hemocompatibility of the resulting membranes was evaluated based on human plasma proteins adsorption, platelet adhesion, thrombus formation, and blood coagulation time. The PAN/PVDF blends exhibited partial miscibility according to the inward shifting of their two glass transition temperatures. The microstructures of blend membranes examined using atomic force microscopy (AFM) indicated that the roughness increased with the PVDF content, and the phase separation was too severe to form a membrane when the PVDF content was more than 30%. The water contact angle of PAN/PVDF blend membranes increased with the PVDF content. By blending with 20 wt% apolar PVDF the adsorption of blood proteins could be reduced, and hence the platelet adhesion and thrombus formation was also reduced. However, when the PVDF content was 30 wt%, severe thrombogenicity was observed due probably to the more porous structure of blend membrane. These results demonstrated that the hemocompatibility would be improved for PAN/PVDF blend membranes with appropriate hydrophilicity and roughness. Copyright © 2005 John Wiley & Sons, Ltd.     

Morphologies and crystalline forms of polyvinylidene fluoride membranes prepared in different diluents by thermally induced phase separation

We have studied the morphologies and crystalline forms of polyvinylidene fluoride (PVDF) membranes separately prepared in four different diluents bearing >C?O groups, namely 1,2‐propylene glycol carbonate (PGC), dimethyl phthalate (DMP), diphenyl ketone (DPK), and dibutyl phthalate (DBP), by the thermally induced phase separation (TIPS) method. The permittivities of the diluents and PVDF were measured to compare the different PVDF–diluent systems. The results showed the permittivity of PGC to be much greater than that of PVDF, and those of DMP and DBP to be lower than that of PVDF. The permittivity difference between DPK and PVDF was not apparent above 120 °C. On cooling mixtures with a PVDF concentration of 10 wt %, PVDF crystallization was observed in the PVDF–DMP, PVDF–DBP, and PVDF–PGC systems, while liquid–liquid phase separation occurred in the PVDF–DPK system. A cross‐section of the PVDF–PGC membrane presented smooth PVDF particles in the β‐phase crystalline form. Those of the PVDF–DMP and PVDF–DBP membranes presented PVDF particles consisting of a fibrillar network in the α‐phase. The PVDF–DPK membrane preferentially adopted an α‐phase bicontinuous channel structure. When the concentration of PVDF was 60 wt %, the cross‐sections of the above four membranes revealed PVDF polyhedra, among which the PVDF–DMP, PVDF–DBP, and PVDF–DPK membranes retained the α‐phase crystalline form, and the diffraction peak of the α‐phase became visible in the X‐ray diffraction (XRD) spectrum of the PVDF–PGC membrane. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

PSSA pore-filled PVDF membranes by simultaneous electron beam irradiation: Preparation and transport characteristics of protons and methanol

Polystyrene sulfonic acid (PSSA) pore-filled poly(vinylidene fluoride) (PVDF) membranes have been prepared using simultaneous electron irradiation method. Porous PVDF films were grafted by pre-swelling in styrene solution and subsequent irradiation with an electron beam (EB) under nitrogen atmosphere and at ambient temperature. The grafted films i.e. polystyrene (PS) pore-filled PVDF were subsequently sulfonated with a diluted mixture of chlorosufonic acid. The effects of the reaction parameters on the content of PS grafted in the pores of PVDF films were investigated. The chemical and morphological properties of the membranes in comparison with their un-grafted and grafted counterparts were studied by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The transport properties of these membranes such as ionic conductivity and methanol permeability were evaluated and correlated with the content of PS grafted in the pores of the PVDF films. The PSSA pore-filled PVDF membranes with PS content in the pores of 40% and above showed superior performance characteristics compared to Nafion 117 membrane and therefore can be potential alternatives to improve the performance of direct methanol fuel cell (DMFC).     

Characterization and evaluation of commercial poly (vinylidene fluoride)‐g‐sulfonatedPolystyrene as proton exchange membrane

The possibility of developing low‐cost commercial grafted and sulfonated Poly(vinylidene fluoride) (PVDF‐g‐PSSA) membranes as proton exchange membranes for fuel cell applications have been investigated. PVDF‐g‐PSSA membranes were systematically prepared and examined with the focus of understanding how the polymer microstructure (degree of grafting and sulfonation, ion‐exchange capacity, etc) affects their methanol permeability, water uptake, and proton conductivity. Fourier transform infrared spectroscopy was used to characterize the changes of the membrane's microstructure after grafting and sulfonation. The results showed that the PVDF‐g‐PSSA membranes exhibited good thermal stability and lower methanol permeability. The proton conductivity of PVDF‐g‐PSSA membranes was also measured by the electrochemical impedance spectroscopy method. It was found that the proton conductivity of PVDF‐g‐PSSA membranes depends on the degree of sulfonation. All the sulfonated membranes show high proton conductivity at 92°C, in the range of 27 to 235 mScm⁻¹, which is much higher than that of Nafion212 (102 mScm⁻¹ at 80°C). The results indicated that the PVDF‐g‐PSSA membranes are particularly promising membranes to be used as polymer electrolyte membranes due to their excellent stability, low methanol permeability, and high proton conductivity.     

In situ preparation of Al-containing PVDF ultrafiltration membrane via sol-gel process

Recently, inorganic nanoparticles blended within polymeric membranes have shown improved antifouling performance in wastewater treatment. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface. In this study, a new method for in situ preparation of Al-containing PVDF ultrafiltration membranes to improve the dispersion of nanoparticles is reported. The strategy of this method is to combine sol-gel process with traditional immersion precipitation process. Al sol was synthesized by the addition of anionic exchange resin in N,N-dimethylformamide (DMF) solvent containing aluminum chloride. Homogeneous Al-containing PVDF casting solution was then obtained by dissolving PVDF polymer in the Al sol. The membrane formation mechanism was investigated by precipitation kinetics and morphology. Results indicate that the addition of Al species can accelerate phase inversion of casting solution. Scanning electron microscopic images show that a typical transition from sponge-like structure to finger-like structure occurred with increasing Al species content. The existence and dispersion states of Al species in the resultant membrane matrix were further examined by transmission electron microscope and X-ray photoelectron spectrometer. The results indicate the Al species nanoparticles were well dispersed throughout PVDF matrix. Dynamic BSA fouling resistance experiments demonstrate the Al-containing PVDF membranes possess improved separation performances over the pure PVDF membranes.     

Hemocompatibility of poly(vinylidene fluoride) membrane grafted with network-like and brush-like antifouling layer controlled via plasma-induced surface PEGylation

In this work, the hemocompatibility of PEGylated poly(vinylidene fluoride) (PVDF) microporous membranes with varying grafting coverage and structures via plasma-induced surface PEGylation was studied. Network-like and brush-like PEGylated layers on PVDF membrane surfaces were achieved by low-pressure and atmospheric plasma treatment. The chemical composition, physical morphology, grafting structure, surface hydrophilicity, and hydration capability of prepared membranes were determined to illustrate the correlations between grafting qualities and hemocompatibility of PEGylated PVDF membranes in contact with human blood. Plasma protein adsorption onto different PEGylated PVDF membranes from single-protein solutions and the complex medium of 100% human plasma were measured by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies. Hemocompatibility of the PEGylated membranes was evaluated by the antifouling property of platelet adhesion observed by scanning electron microscopy (SEM) and the anticoagulant activity of the blood coagulant determined by testing plasma-clotting time. The control of grafting structures of PEGylated layers highly regulates the PVDF membrane to resist the adsorption of plasma proteins, the adhesion of platelets, and the coagulation of human plasma. It was found that PVDF membranes grafted with brush-like PEGylated layers presented higher hydration capability with binding water molecules than with network-like PEGylated layers to improve the hemocompatible character of plasma protein and blood platelet resistance in human blood. This work suggests that the hemocompatible nature of grafted PEGylated polymers by controlling grafting structures gives them great potential in the molecular design of antithrombogenic membranes for use in human blood.     

High yield electroblotting onto polyvinylidene difluoride membranes from polyacrylamide gels.

Optimal conditions of electroblotting that led to high protein recovery on polyvinylidene difluoride (PVDF) membranes were determined for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). SDS concentrations in the gel and transfer buffer were found to be the most important factors affecting the amount of protein recovered on the PVDF membrane. The largest loss occurred during the first 10-30 min of transfer due to the relatively high initial SDS concentration in the gel. During this initial stage of transfer, most of the protein passed through the primary membrane and was partially retained on secondary and tertiary membranes. The value of presoaking gels prior to transfer to reduce the amount of SDS was evaluated by quantitating free SDS densitometrically and by correlating the reduced SDS concentration with increased electroblotting efficiency from presoaked gels. Transfer time was evaluated and no "overtransfer" was found even after very long transfer times. These results clearly indicate that proteins electroblotted onto PVDF membranes were tightly bound and could not be released by extending the transfer time. The effects of methanol and SDS concentrations on protein adsorption from solution to PVDF were also determined quantitatively. The results of this study strongly suggest that proteins fully saturated with SDS cannot bind efficiently to PVDF membranes. Since SDS is necessary for high protein mobility, the challenge in efficient electroblotting is to maintain an optimal SDS concentration which is high enough to permit effective removal from the gel and low enough to permit effective binding to the PVDF membrane. For 1.5 mm thick gels containing 0.2% SDS, presoaking the gel for 15-20 min in transfer buffer with 10% methanol prior to electroblotting provided the best recovery on the primary membrane.     

Phenotyping of apolipoprotein E by immunoblotting in immobilized pH gradients

An immunoblotting method for the determination of apolipoprotein E (apoE) phenotypes has been developed. Delipidated plasma proteins are focused in an immobilized pH gradient, and transferred to polyvinylidene difluoride (PVDF) membranes. ApoE isomorphs are identified by immunoperoxidase staining. The method allows reproducible assignment of apoE phenotypes without isolation of triglyceride-rich lipoproteins. Only small amounts of serum are required. There are several important steps in the procedure: (i) delipidation is indispensable, (ii) carrier ampholytes have to be added to the gels and to the sample buffer, and, (iii) on immunostaining, polyvinylidene difluoride membranes provide an excellent signal-to-background ratio.     

聚偏氟乙烯-磺化聚醚砜相容性及其成膜性能

研究了聚偏氟乙烯(PVDF)-磺化聚醚砜(SPES)的相容性及其成膜性能.首先通过溶解度参数、粘度法和目测法研究共混溶液的相容性,接着采用浊度法测定了共混溶液的热力学性质,最后采用浸没沉淀法制备了共混膜并探讨了成膜性能.结果显示,PVDF和SPES为部分相容体系,随着SPES含量的增加,共混溶液相容性逐渐减小,当SPES含量增加到50wt%时,体系发生分相.共混溶液的成膜性能良好,SPES含量增加有利于体系发生液液分相,生成高孔隙率膜,并且极大的提高了PVDF膜的亲水性和水通量.     

Amino acids functionalized graphene oxide for enhanced hydrophilicity and antifouling property of poly(vinylidene fluoride) membranes

Herein, functionalized graphene oxide (GO) was prepared by the covalent functionalization with amino acids (lysine, glycine, glutamic acid and tyrosine) in this study. Zeta potential results demonstrated that covalent functionalization of GO with amino acids was favourable for their homogeneous dispersion in water and organic solvents. Based on the higher absolute value of zeta potential and the better dipersion stability of GO-lysine, the PVDF/GO-lysine hybrid membranes were then prepared via the phase inversion induced by immersion precipitation technique. SEM images showed a better pore diameter and porosity distribution on the PVDF/GO-lysine membrane surface. The zeta potential absolute value of the PVDF/GO-lysine membrane surface was higher than that of the virgin PVDF membrane. Furthermore, the PVDF/GO-lysine membranes surface exhibited good hydrophilicity. The water flux of PVDF/GO-lysine membranes can reach to two times of that of the virgin PVDF membrane. And the BSA adsorbed amount on PVDF/GO-lysine surface was decreased to 0.82 mg/cm² for PVDF/GO-lysine-8% membrane. Filtration experiment results indicated that the fouling resistance was significantly improved for the PVDF/GO-lysine membranes. As a result, lysine functionalized GO will provide a promising method to fabricate graphene oxide based hybrid membranes with effective antifouling property and hydrophilicity.     

Improvement in the blood compatibility of polyvinylidene fluoride membranes via in situ cross‐linking polymerization

In this study, we have provided a highly efficient, convenient, and universal protocol for preparing polyvinylidene fluoride (PVDF) membranes with low blood contact activation via in situ cross‐linking copolymerization of 2‐hydroxyethl methacrylate (HEMA) and acrylic acid (AA) in a solution of PVDF. The modified membranes were prepared from PVDF solution by phase inversion technology. The composition and morphology of the modified membranes were confirmed by attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR) spectroscopy, thermogravimetric (TG) analysis, and scanning electron microscopy (SEM). Protein adsorption, clotting time, and contact activation on the modified PVDF membranes were systematically studied, the results indicating that after the incorporation of AA and HEMA, the modified PVDF membranes possessed anticoagulant properties in addition to low contact activation of blood components when in contact with blood. Therefore, fluorinated PVDF membranes with surfaces enriched with carboxyl and hydroxyl groups possessed the potential for use in long‐term blood‐contacting devices.     

Preparation of polyvinylidene fluoride/modified attapulgite composite ultrafiltration membrane

Some modified attapulgites (ATPs), such as surface modified by amino (‐NH₂) or polymethylmethacrylate (PMMA) were used to prepare polyvinylidene fluoride (PVDF)/ATP composite ultrafiltration membranes by nonsolvent induced phase separation method. The excellent compatibility between PMMA or amino and PVDF may promote the dispersion of ATP in PVDF. The thermal, mechanical, hydrophilic, and micro‐morphology of the composite ultrafiltration membranes were characterized. The results showed that with the addition of the modified ATP, the properties of the membranes, such as mechanical and hydrophilic, were improved. When the content of ATP‐g‐PMMA was 2%, the overall performance of the PVDF composite membranes was the best.     

Sorption and diffusion of methanol and water in PVDF‐g‐PSSA and Nafion® 117 polymer electrolyte membranes

Sorption and diffusion properties of poly(vinylidene fluoride)‐graft‐poly(styrene sulfonic acid) (PVDF‐g‐PSSA) and Nafion® 117 polymer electrolyte membranes were studied in water/methanol mixtures. The two types of membranes were found to have different sorption properties. The Nafion 117 membrane was found to have a maximum in‐solvent uptake around 0.4 to 0.6 mole fraction of methanol, while the PVDF‐g‐PSSA membranes took up less solvent with increasing methanol concentration. The proton NMR spectra were recorded for membranes immersed in deuterated water/methanol mixtures. The spectra showed that the hydroxyl protons inside the membrane exhibit resonance lines different from the resonance lines of hydroxyl protons in the external solvent. The spectral features of the lines of these internal hydroxyl groups in the membranes were different in the Nafion membrane compared with the PVDF‐g‐PSSA membranes. Diffusion measurements with the pulsed field gradient NMR (PFG‐NMR) method showed that the diffusion coefficient of the internal hydroxyl groups in the solvent immersed Nafion membrane mirrors the changes in the diffusion coefficients of hydroxyl and methyl protons in the external solvent. For the PVDF‐g‐PSSA membranes, a decrease in the diffusion coefficient of the internal hydroxyl protons was seen with increasing methanol concentration. These results indicate that the morphology and chemical structure of the membranes have an effect on their solvent sorption and diffusion characteristics. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3277–3284, 2000     

Flow and evaporation cells for the detection of proteins on membranes with the peroxyoxalate chemiluminescent reaction in organic media

The high-energy intermediates generated in the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with H2O2 can excite electronically different fluorophores with a high quantum yield in organic solvents. We have previously applied this peroxyoxalate chemiluminescent reaction to the detection of proteins labeled with the fluorescent dye 2-methoxy-2,4-diphenyl-3(2H)-furanone (MDPF) on polyvinylidene difluoride (PVDF) membranes. In this work, we have investigated the possibility to enhance the sensitivity of this detection method using specially designed cells in which the reagents TCPO and H2O2 in acetone are continuously renewed. In the flow cell, two syringes are used to renew the reagents in the reaction chamber containing the PVDF membrane with blotted proteins labeled with MDPF. In the evaporation cell, a fresh solution of reagents continuously replaces the volume of acetone evaporated in the reaction chamber. Both cells show a low emission background but the observed elution of proteins from the membrane produced by the flow of reagents in acetone limits the maximum sensitivity attainable with these cells. The best result (detection of 1 ng of MDPF-labeled protein) has been obtained with the evaporation cell.     

Radiation grafted poly(vinylidene fluoride)-graft-polystyrene sulfonic acid membranes for fuel cells: Structure-property relationships

<正>Structure-property relationships for poly(vinylidene fluoride)-graft-polystyrene sulfonic acid(PVDF-g-PSSA) fuel cell membranes prepared by a single step method involving radiation-induced grafting of sodium styrene sulfonate(SSS) onto electron beam(EB) irradiated poly(vinylidene fluoride)(PVDF) films were established.The physico-chemical properties of the membranes such as ion exchange capacity,water swelling and proton conductivity were correlated with the degree of grafting(G,%) and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity and the thermal stability of membranes was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis(TGA),respectively.The membranes were found to undergo substantial structural changes in forms of ionic sites increase,hydrophilicity enhancement,hydrophobicity reduction and crystallinity decrease with the variation in G(%) and the preparation method.The structural and thermal properties of the obtained membranes were also compared with their counterparts prepared by a conventional two-steps method i.e.radiation induced grafting of styrene onto EB irradiated PVDF films followed by sulfonation.The PVDF-g-PSSA membranes obtained by a single-step method were found to have superior properties compared to those obtained by the conventional two-steps method.     

Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone-added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Polyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method from casting solutions containing PVDF, dimethylformamide (DMF), and polyvinylpyrrolidone (PVP) as pore former. PVP was used in the casting solution in a range of 0–5 wt % and extracted. The effect on membranes of using PVP in the casting process was analyzed by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, viscosity, and water permeability techniques. With an increase of PVP from 0 to 5 wt %, the PVDF casting solution viscosities increased from 858 to 1148 cP; the resulting PVDF membrane thickness increased; and the crystallinity of PVDF membranes decreased from 40.0 to 33.3%, which indicates that the addition of PVP inhibits the degree of crystallization in the PVDF membranes. SEM results revealed the shape and size of macropores in the membranes; these macropores changed after PVP addition to the casting solutions. The impact of structural changes on free-volume properties was evaluated using positron annihilation lifetime spectroscopy (PALS) studies. PALS analysis indicated no effect on the average radius (~3.4 Å) of membrane free-volume holes from the addition of PVP to the casting solution. However, the percentage of o-Ps pick-off annihilation intensity, I₃, increased from 1.7 to 5.1% with increased PVP content. Further, increasing the PVP content from 0.5 to 5% resulted in an increased final pure water permeability flux. For instance, the 210 min flux for a 14% PVDF + 0.5% PVP membrane was found to be 3.3 times greater than a control membrane having the same PVDF concentration. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 589–598     

纳米Fe3O4/PVDF磁性复合膜的原位制备及表征

通过膜相渗透原位化学沉积法制备了聚合物基Fe3O4/聚偏氟乙烯（PVDF）磁性纳米复合膜，研究了复合膜制备的适宜条件，采用红外光谱（FT-IR）、差热分析（DSC）、X射线衍射、扫描电镜（SEM）等手段对复合膜的组成、结构进行了表征和分析，通过气体渗透法测定了复合膜的孔径随制备条件的变化情况. FT-IR和XRD图谱结果表明，在基膜中原位生成Fe3O4后不影响基膜PVDF的分子结构；复合膜中的Fe3O4粒子尺寸为68 nm左右，复合膜的磁化率达0.044 cm3•g－1；复合膜的磁化率、平均孔径、最大孔径及孔径分布范围随反应条件的改变而有明显变化.     

Preparation and characterization of polyvinylidene fluoride (PVDF) hollow fiber membranes

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared by dry/wet and wet phase inversion methods. In spinning these PVDF hollow fibers, dimethylacetamide (DMAc) and polyvinyl pyrrolidone (PVP) were used as a solvent and an additive, respectively. Water was used as the external coagulant. Water or ethanol was used as the internal coagulants. The membranes were characterized in terms of water flux, molecular weight cut-off for the wet membranes. Gas permeation fluxes and effective surface porosity were determined by a gas permeation method for the dried membranes. The cross-sectional structures were examined by scanning electron microscopy. The effects of polymer concentration, air-gap, PVP molecular weight, PVP content in the polymer dope, and the internal coagulant on the permeation properties and membrane structures were examined. Highly permeable PVDF hollow fiber membranes could be prepared from a polymer dope containing low molecular weight PVP and using ethanol as the internal coagulant.     

Biofouling resistance of ultrafiltration membranes controlled by surface self-assembled coating with PEGylated copolymers

Block and random PEGylated copolymers of poly(ethylene glycol) methacrylate (PEGMA) and polystyrene (PS) were synthesized with a controlled polydispersity using an atom transfer radical polymerization method and varying molar mass ratios of PS/PEGMA. Two types of PEGylated copolymers were self-assembly coated onto the surface of poly(vinylidene fluoride) (PVDF) ultrafiltration membranes for enhancing biofouling resistance. It was found that the adsorption capacities of random copolymers on PVDF membranes were all higher than those of block copolymers. However, the specific and overall protein resistance of bovine serum albumin (BSA) on PVDF membranes coated with block copolymers was much higher than that with random copolymers. The increase in styrene content in copolymer increased the amount of polymer coating on the membrane, and the increase in PEGMA content enhanced the protein resistance of membranes. The optimum PS/PEGMA ratio was found to be close to 2 for the best resistance of protein adsorption and bacterial adhesion on the PEGylated diblock copolymer-coated membranes. The PVDF membrane coated with such a copolymer owned excellent biofouling resistance to BSA, humic acid, negatively surface charged bacteria E. coli, and positively surface charged bacteria S. maltophilia.     

Evolution of the precipitation kinetics,morphologies, permeation performances,and crystallization behaviors of polyvinylidenefluoride (PVDF) hollow fiber membrane by adding different molecular weight polyvinylpyrrolidone (PVP)

Polyvinylidenefluoride (PVDF) hollow fiber membranes were fabricated by wet spinning (wet/wet) and dry‐jet wet spinning (dry/wet; 3 cm air gap) processes with four types of polyvinylpyrrolidone (PVP) of different molecular weight as additives. Evolution of the precipitation kinetics, morphologies, permeation performances, and crystallization behaviors of the as‐spun PVDF membranes were investigated. The PVDF membranes were well characterized by numerous state‐of‐the‐art analytical techniques: scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and attenuated total reflectance fourier Transform Infrared (FTIR‐ATR) and elucidated accompanying with its precipitation kinetics obtained by light transmittance measurements. The precipitation kinetics results confirm that four PVDF/PVP/NMP dopes experience instantaneous demixing mechanism and the precipitation rate decreases as PVP molecular weight increases. Little peaks are found in the precipitation curves of the PVDF dopes containing PVP of low molecular weight. The SEM images indicate that the middle sponge‐like layer sandwiched by double finger‐like layers becomes thinner for the special precipitation behaviors. Visible large pores exist in the internal surfaces of the PVDF membranes spun by both wet/wet and dry/wet spinning processes. The increase in PVP molecular weight restricts the formation of large pores in the internal surfaces of the PVDF membranes for the increase in dope viscosity. The pure water permeability (PWP) of the as‐spun PVDF membranes increases initially and then decreases as PVP molecular weight increases. The largest PWP flux of 316.7 L m^?2 h^?1 bar^?1 is obtained for the PVDF membrane containing PVP K25 by wet/wet spinning process. The rejections for bovine serum albumin (BSA) by the as‐spun PVDF membranes range from 35.4 to 82.9%. It illustrates that typical PVDF ultrafiltration membranes were obtained in this research. The melting temperature(T_m) of the PVDF hollow fiber membranes decreases with the increase in the PVP molecular weight as a whole. IR spectra and XRD patterns verify the exclusive formation of β crystalline phase structure in the as‐spun PVDF membranes. Copyright © 2010 John Wiley & Sons, Ltd.