Characterization of PVDF–PFSA hollow fiber UF blend membrane with low-molecular weight cut-off

Abstract

Polyvinylidene fluoride (PVDF)–perfluorosulfonic acid (PFSA) hollow fiber ultrafiltration blend membranes were prepared by wet-spinning method. The effects of PVDF–PFSA and ethanol concentrations on the structure morphology and performance of blend membranes were investigated. The coagulation kinetics was studied by light transmittance experiments. Blend membranes were characterized in terms of morphology, pore size distribution, molecular weight cut-off, water permeation flux and rejection. The wetting and fouling properties of blend membranes were also examined. Based on the experimental results, more sponge-like structures existed in the cross section of the blend membrane prepared from the dope solution with the increase in PVDF concentration, but the membrane showed a worse permeation performance. The increase of PFSA resulted in the formation and development of the finger-like voids. It was also found that the finger-like macrovoids began growing up inside the nascent membrane. Such changes were proved by scanning electron microscopy (SEM). By introducing different concentrations of ethanol from 1 to 5 wt.% in PVDF–PFSA dope solution, thinner and more uniform finger-like voids appeared through the cross section, the pure water permeation flux, the mean effective pore size, molecular weight cut-off were increased. PVDF–PFSA hollow fiber UF blend membranes with low-molecular weight cut-off around 10,000 Da were obtained and the morphology was elaborately controlled.