STRUCTURAL INVESTIGATION OF RADIATION GRAFTED AND SULFONATED POLY(VINYLIDENE FLUORIDE), PVDF, MEMBRANES

Radiation grafted and sulfonated poly(vinylidene fluoride), PVDF, memb ranes have been studied by thermal analysis and X-ray diffraction to d etermine the changes in membrane crystallinity and structure during pr eparation. Commercial PVDF films were irradiated with an electron beam , grafted with styrene and finally sulfonated. Both the crystallinity and the size of the crystallites of PVDF decrease in the grafting reac tion. A further decrease in crystallinity is observed in the sulfonati on reaction. The residual crystallinity of PVDF was considerable (10-2 0%) even in membranes which had been subjected to severe reaction cond itions. These results can be explained by assuming that the grafting t akes place mainly in the amorphous region of the PVDF, and close to th e surfaces of the crystals, but that grafts do not penetrate into the crystals. The proton conductivity of the grafted and sulfonated PVDF m embranes reached values comparable to those of Nafion membranes.