Electron-beam Graft-modified Membranes with Externally Controlled Flux

Abstract

Pre-irradiation grafting as a means to modify commerical poly(vinylidene fluoride) (PVDF) membranes has been studied. The membranes prepared were weak cation-exchange membranes (acrylic acid functionality), anion-exchange membranes (trimethyl ammonium functionality) and temperature-sensitive membranes (N-isopropyl amide functionality). Different graft loads were obtained by varying reaction time, radiation dose and in the case of acrylic acid the graft solution composition. The trimethyl ammonium chloride functionality was obtained by grafting vinyl benzyl chloride onto a PVDF membrane and aminating the benzyl chloride groups in a 45% trimethyl amine–water solution. For a membrane grafted with 9 wt% acrylic acid the flux increased approximately 70 times when the pH was decreased from 6 to 2. For a membrane with 5 wt% trimethyl ammonium functionality the flux increased both when pH was decreased below 3 and increased above 11. For a membrane grafted with 18 wt% N-isopropyl acrylamide a sharp increase of flux was observed when the temperature was raised above 32°C.