Preparation Of Poly (Vinylidene Fluoride) (PVDF) Hydrophilic Membranes By Ozone-Induced Graft Copolymerization

Poly(vinylidene fluoride) (PVDF) has many desirable properties including chemical inertness, thermal stability, favorable mechanical strength and low cost. However, its inherent hydrophobic characteristics made it vulnerable to fouling, thus its application is limited. So, the membrane material needs to be modified to improve its hydrophilicity. In this paper, peroxide groups were introduced into PVDF molecules in N-methyl-2-pyrrolidone (NMP) solution by ozone treatment; then acrylic acid (AAc) was grafted onto ozone-treated PVDF via thermally induced grafting, and then hydrophilic PVDF membranes were prepared via phase inversion. The structure and properties of the modified PVDF were characterized by IR and contact angle. The IR spectra showed that the-C=O- characteristic peak at the wave number of 1709 cm-1 was detected, which proved that the hydrophilic substance was successfully introduced. The modified PVDF membranes had lower surface water contact angle and better hydrophilicity. The effect of grafting conditions was studied, and the results showed that hydrophilicity increased as the concentration of the monomer increased. The scanning electron microscopy (SEM) micrographs showed that the surface appearances of the modified membranes and the original membranes prepared under equivalent conditions differed greatly:the modified membranes showed larger pores, and the pore size and density were affected by ozone treatment time and the concentration of added AAc. The water flux increased greatly after grafting. Then the hollow fibers were prepared by dry-wet spinning. This research focused on how the ozone treatment time affected the hydrophilicity of modified PVDF hollow fibers. Experimental results indicated that, comparing with pristine PVDF hollow fiber, the modified PVDF hollow fibers had specific structure, lower water contact angle and higher water flux.