Synthesis and characterization of positively charge-modified polyproplyene membrane

A technique for incorporating positively charged groups onto the surface of microporous polypropylene membrane filters is described. In this method, 4-vinyl-pyridine is polymerized and grafted onto polypropylene membranes using ⁶⁰Co γ-irradiation. Pyridyl groups on the grafted membranes are quaternized with butyl bromide. 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 is 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 test at a pH of 5.0, the density of positively charged sites was calculated to be 1.7×10¹⁹ sites/g. The membranes did not release any measureable total oxidizable carbon (TOC) into ultrapure water and thus appear to have potential for use in deionized (DI) water system