Effect of surface charge on hydrophilically modified poly(vinylidene fluoride) membrane for microfiltration

Charged poly(vinylidene fluoride) microfiltration membranes were prepared using stepwise chemical modification of defluorination and sulfonation. Different degrees of sulfonation with respect to degree of defluorination were controlled by varying the alcoholic potassium hydroxide concentration, reaction temperature and time. The effects of surface modification on the morphology, zeta potential, ion-exchange capacity (IEC), hydrophilicity, pure water flux, fouling, and rejection were investigated. As the degree of surface charge density increased, the IEC and hydrophilicity increased without any deformation on the morphology and pores as observed through scanning electron microscopy (SEM). The surface composition of sulfonic acid groups on the modified membrane was determined by X-ray photoelectron spectroscopy (XPS). As the concentration of sulfonic acid groups increased with the degree of surface charge density, the zeta potentials of membrane surface increased. It was also observed that the pure water flux was enhanced as the intrinsic resistance decreased with different degrees of surface charge density. Fouling of charged polystyrene latex suspension on the modified membrane decreased while rejection value increased as the degree of surface charge density was increased due to enhanced electrostatic repulsion. (C) 2010 Elsevier B.V. All rights reserved.