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.