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 devel oped. In this method, a water-soluble vinyltriphenylphosphonium bromid e compound was grafted onto polyvinylidene fluoride membranes using Co -60 gamma-irradiation. The electrical characteristics of prepared memb ranes were measured by streaming potential and anionic dye challenge t ests. The compatibility of these charge-modified membranes with ultrap ure water was also investigated. Results show that these charge-modifi ed 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 posit ively charged sites was calculated to be approximately five times larg er than that of unmodified polyvinylidene fluoride. The modified membr anes released less than 1 ppb of total organic carbon (TOC) into ultra pure water and thus appear to have potential for use in DI water syste ms.