Microporous Poly Vinylidene Fluoride Research Articles

Chromatographic separation of proteins using hydrophobic membrane shielded with an environment-responsive hydrogel

Environment-responsive membranes, suitable for carrying out hydrophobic interaction membrane chromatography (HIMC) were prepared by modification of a commercial hydrophobic microporous polyvinylidene fluoride (PVDF) membrane with a salt-responsive hydrogel composed of poly(N-vinyl lactam) cross-linked with bisacrylamide. These modified membranes were moderately hydrophobic in the presence of lyotropic salts but were quite hydrophilic in their absence. The membranes were characterized in terms of their mass gains after modification as well as their contact angles. These new membranes were found to be suitable for carrying out monoclonal antibody purification.

Formation of a bicontinuous structure membrane of polyvinylidene fluoride in diphenyl carbonate diluent via thermally induced phase separation

AbstractDiphenyl carbonate was used as a diluent to prepare microporous polyvinylidene fluoride (PVDF) membrane via thermally induced phase‐separation method. The liquid–liquid phase‐separation phenomenon was found in PVDF/diphenyl carbonate system during the thermally induced phase‐separation process. The monotectic point of this system appeared at a high polymer concentration approximately 56 wt %. This suggested that PVDF membrane with a bicontinuous or cellular structure could be obtained when the PVDF concentration was less than this point value. The effects of polymer concentration and quenching temperature on the membrane structure, porosity, and tensile strength were also investigated. The results showed that low polymer concentration and high quenching temperature led to a large pore size membrane. The tensile strength of the membrane increased with increase in the polymer concentration, but the porosity of the membrane decreased. On condition that the PVDF concentration was higher than 60 wt %, only polymer crystallization occurred and a typical compact spherulitic structure was obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Extraction of surfactin from fermentation broth with n-hexane in microporous PVDF hollow fibers: Significance of membrane adsorption

Abstract In order to avoid foaming behavior and the formation of stable emulsions in traditional extraction, non-dispersive extraction of surfactin from the fermentation broth of Bacillus subtilis ATCC 21332 culture with n-hexane was studied in microporous polyvinylidene fluoride (PVDF, pore size 0.2 μm) hollow fiber module. In this work, the broth was pretreated by acid precipitation and the precipitate was then dissolved in NaOH solution, and the treated broth was passed through the lumen side of the module and n-hexane was flowed across the shell side. Experiments were performed at a fixed pH of 8.0 and a flow rate of both phases of 2.5 mL min−1 but at different surfactin concentrations (300–3000 mg L−1). Under the conditions studied, it was shown that surfactin was adsorbed onto the surface of the fibers, instead of being extracted by n-hexane and transported through the pores of the fibers into bulk n-hexane phase. The adsorption capacity was determined and the adsorption dynamics was analyzed. The purity of surfactin desorbed from the fibers with ethanol was found to be higher than that obtained after solvent extraction with n-hexane.

Membranes of Polyvinylidene Fluoride and PVDF Nanocomposites with Carbon Nanotubes via Immersion Precipitation

Microporous polyvinylidene fluoride (PVDF) and PVDF nanocomposite membranes were prepared via an isothermal immersion precipitation method using two different antisolvents (ethanol and water). The structure and morphology of the resulting membranes were investigated by wide angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The effects of the type of the antisolvent and the presence of multiwalled carbon nanotubes (MWNTs) on membrane morphology and the crystal structure developed within the membranes were studied. The crystallization of the PVDF upon immersion precipitation occurred predominantly in the α‐phase when water is used as the antisolvent or in the absence of the carbon nanotubes. On the other hand, β‐phase crystallization of the PVDF was promoted upon the use of ethanol as the antisolvent in conjunction with the incorporation of the MWNTs. The morphology and the total crystallinity of the PVDF membranes were also affected by the incorporation of the MWNTs and the antisolvent used, suggesting that the microstructure and the ultimate properties of the PVDF membranes can be engineered upon the judicious selection of crystallization conditions and the use of carbon nanotubes.

Absorption of SO2 using PVDF hollow fiber membranes with PEG as an additive

In this study, removal of SO2 from gas stream was carried out by using microporous polyvinylidene fluoride (PVDF) asymmetric hollow fiber membrane modules as gas-liquid contactor. The asymmetric hollow fiber membranes used in this study were prepared polyvinylidene fluoride by a wet phase inversion method. Water was used as an internal coagulant and external coagulation bath for all spinning runs. An aqueous solution containing 0.02 M NaOH was used as the absorbent. This study attempts to assess the influence of PEG additive, absorbent flow rate, SO2 concentration, gas flow rate and gas flow direction on the SO2 removal efficiency and overall mass transfer coefficient. The effect of liquid flow rate on SO2 removal efficiency shows that at very low liquid flow rate, the NaOH available at the membrane surface for reacting with SO2 is limited due to the liquid phase resistance. As liquid flow rate is above the minimum flow rate which overcomes the liquid phase resistance, the SO2 absorption rate is controlled by resistance in the gas phase and the membrane. The SO2 absorption rate with inlet SO2 concentration was sharply increased by using hollow fiber membranes compared to a conventional wetted wall column because the former has higher gas liquid contacting area than the latter. The mass transfer coefficient is independent of pressure. When the gas mixture was fed in the shell side, the removal efficiency of SO2 declined because of channeling problems on the shell side. Also, the addition of PEG in polymer dopes increased SO2 removal efficiency.

Preparation of divinyl-PDMS/PVDF composite hollow fibre membranes for BTX removal

Microporous polyvinylidene fluoride (PVDF) hollow fibre membranes spun using the dry–wet phase inversion method were coated with cross-linkable divinyl-terminated silicone rubber, divinyl-polydimethylsiloxane (divinyl-PDMS). Cross-sectional structure of the composite membranes formed was examined using scanning electron microscopy (SEM), displaying a uniform coating thickness of approximately 5–7 μm. Oxygen/nitrogen selectivity over 2.24 was obtained, indicating successful formation of selective coating layer. Removal of benzene, toluene and xylene (BTX) from hydrocarbon/nitrogen mixtures was tested at a temperature of 40 °C using the composite hollow fibre membrane developed.

Membrane Surface for Carbohydrate Analysis

Abstract A poly(methyldiallylamine-chlorohydrin) polymer was used to surface modify microporous PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and UPE (ultra high molecular weight polyethylene) membranes. These membranes were used to covalently bond hydrophilic charged carbohydrate molecules. The surfaces were characterized in terms of the structural variations of the monomer units. Immobilization occurs by a two-step process whereby strong imagewise electrostatic forces bring nucleophile (charged carbohydrate conjugate) and electrophile (membrane surface desorptive media groups) into close proximity for a pH triggered reaction to covalently bond the carbohydrate. The immobilization potential of the surfaces is described by the chlorohydrin and epoxy groups available for reaction, and is inversely proportional to the amount of alkali employed during membrane surface modification. Conjugation of complex carbohydrate mixtures to a charged fluorophore, followed by electrophoresis, transfer to the membrane surface, and immobilization produced covalently bonded bands, enabling carbohydrate structural analysis in highly desorptive media.

Surface modification of PVDF membranes by grafting of a vinylphosphonium compound

A technique to incorporate positively charged groups onto the surface of microporous polyvinylidene fluoride membrane filters has been developed. In this method, a water-soluble vinyltriphenylphosphonium bromide compound was grafted onto polyvinylidene fluoride membranes using 60Co γ-irradiation. The electrical characteristics of prepared membranes were measured by streaming potential and anionic dye challenge tests. The compatibility of these charge-modified membranes with ultrapure water was also investigated. Results show that these charge-modified membranes are characterized by a positive zeta potential in the pH range from 4 to 9.3. From the dye challenge tests the density of positively charged sites was calculated to be approximately five times larger than that of unmodified polyvinylidene fluoride. The modified membranes released less than 1 ppb of total organic carbon (TOC) into ultrapure water and thus appear to have potential for use in DI water systems.

The formation of microporous polyvinylidene difluoride membranes by phase separation

Microporous polyvinylidene fluoride (PVDF) membranes were prepared by casting and coagulating solutions of the polymer in eight different solvents. The membranes were characterized by scanning electron microscope observations, water content measurements and water permeability tests. The possible correlations between the resulting membrane characteristics and the properties of both the polymer-solvent solutions and the solvent-nonsolvent systems are extensively discussed. The analysis indicates that most of the correlations suggested or adopted in the literature do not hold for PVDF membranes, whereas the transport properties of the solvent-nonsolvent system seem to affect significantly the final membrane structure and the resulting performances in separation processes.

Evaluation of a new microporous filtration membrane system for therapeutic plasma exchange.

A new therapeutic plasma exchange device developed by Sarns Inc./3M was evaluated in plasmapheresis of 20 healthy volunteers and in a multicenter clinical study of therapeutic plasma exchange that included 49 patients. Safety and efficacy of plasma separation from whole blood were assessed for a module that contains Durapore microporous surfactant-free polyvinylidene fluoride membrane (Millipore Corp., Bedford, Mass., USA). The extra-corporeal volume was 80 ml. Citrate and heparin anticoagulants were utilized. Mean plasma separation efficiency was 62% with unhindered passage of plasma proteins through the membrane pores and no hemolysis or activation of complement as measured by total hemolytic complement (CH50) and C3 conversion. Mean decrease in platelet count after procedures was 10%. No severe reactions occurred, and citrate effects (13%) were comparable to values reported with centrifugal instruments. The Sarns Inc./3M Therapore device is a rapid, safe and efficient system for plasma exchange and potentially for source plasma collection. The principal benefits are small extracorporeal volume and cell-free filtrate.