Synthesis and Characterization of Postively Charge-Modified Polypropylene Membranes

A technique to incorporate positively charged groups onto the surface of microporous polypropylene membrane filters has been developed. In this method, 4-vinyl-pyridine was polymerized and grafted onto polypropylene membranes using ⁶⁰Co γ-irradiation. Pyridyl groups on the grafted membranes were then 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 was 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 x 10¹⁹ sites/g. The membranes did not release any measurable TOC into ultrapure water and thus appear to have potential for use in DI water systems.