PREPARATION AND PERFORMANCE OF MODIFIED POLYVINYLIDENE FLUORIDE MEMBRANES GRAFTED WITH SULFONATED POLY(STYRENE-co-ACRYLIC ACID)

Polyvinylidene fluoride membranes grafted with sulfonated poly(styrene-co-acrylic acid) (PVDF-g-P(SSA-co-AA)) were prepared by a solution-grafting technique. In the technique, benzoylperoxide (BPO) was used as an evocating agent, and polystyrene and acrylic acid were grafted onto PVDF membranes modified with plain sodium silicate (Na4SiO4), then, the product was sulfonated to obtain PVDF-g-P(SSA-co-AA) membranes. The effects for the different ratio of styrene and acrylic acid on the grafting degree, and their humidity on the conductivity of membrane and the moisture content, were investigated. Fourier transform infrared spectroscopy (FTIR) was used to characterize the change of the membrane's microstructures before and after the grafting and the sulphonation. The morphologies of the PVDF and the PVDF-g-P(SSA-co-AA) membranes and the distribution of silicon were studied by scanning electrolytic microscope (SEM). The results indicated that the conductivity of PVDF-g-P(SSA-co-AA) membrane doped with 10 wt% Na4SiO4 was 0. 0198 S.cm(-1) at a relative humidity range of 20% similar to 80%, and the microstructures of PVDF membrane modified with plain sodium silicate (Na4SiO4) after the grafting and the sulphonation changed obviously, which indicated that the sulphonation had permeated into the membrane besides the membrane surface.