The Preparation And Properties Of Sulfonated Poly (Vinidene Difluoride) Grafted Polystyrene Ion Exchange Membranes

In this paper, sorts of the modification of PVDF membrane were extensively reviewed and analyzed, and on this basis, the modifications of alkaline treatment, graftion and sulfonation were selected as the methods of the preparation. The study aimed to prepare the ion exchange membranes with better characteristics, preparing the PVDF-g-Polystyrene Sulfonated Acid (PVDF-g-PSSA) membranes. The permselectivity of different cations of the sulfonated membranes were studied. The influences of the conditions of alkaline treatment, graftion and sulfonation to prepare membranes were studied.Firstly, the PVDF membranes were treated by the alkaline solutions with the phase transter catalysts tetrabutyl ammonium bromide (TBAB). The study results showed that with the increasing of the concentration of KOH, TBAB, temperature and time, the intensity of the membranes descended. The PVDF and modified membranes were carried out by Fourier transform adsorption spectrum (FTIR) to determine the composition of the membranes. The study indicated the modified membranes with the formation of a surface layer consisting of C=C bonds and hydroxyl groups. Also the morphology of the membranes were determined by Scanning electron microscope (SEM), the results showed that the structureof the membranes were not changed too much.Then, with the solicitation medium benzoyl peroxide (BPO), the styrene monomers were grafted on the modified membranes, and the PVDF-graft-Polystyrene (PVDF-g-PS) membranes were prepared. The study showed the degree of grafting was affected by the conditions of the alkaline treatment. With the increasing of the concentration of KOH and time, the degree of grafting increased and then descended. With the increasing of the concentration of TBAB and temperature, the degree of grafting increased. After determining the influences of the conditions of alkaline treatment to the intensity of the membranes and the degree of grafting, the optimum coditions for alkaline treatment were found to be 7=60℃, t=15min, ρ(TBAB)=3mg/ml, c(KOH)=1.0mol/L, d.o.g =35%. The grafting groups determined by FTIR and SEM were on the membranes.Then, the PVDF-g-PS membranes were sulfonated by sulfuric acid. And the PVDF-g-Polystyrene Sulfonated Acid (PVDF-g-PSSA) membranes were prepared. The study showed the sulfonation degree of the membranes influenced the capabilities. With the increasing of the sulfonation degree, Ion Exchange Capacity (IEC), water content, swelling rate, conductivity increased, permselectivity and intensity increased and then descended. After determining the influences of the conditions of sulfonation to the capabilities of the PVDF-g-PSSA membranes, the optimum coditions for sulfonation were found to be r=70℃, t=90min. With these conditions, the capabilities of the PVDF-g-PSSA membranes were: Ion Exchange Capacity =1.54mmol/g, water content (%) =28.8%, swelling rate (%)= 7.26%, permselectivity= 0.89, conductivity = 0.052S/cm sulfonation degree=1.98mmol/L, intensity (dry)=18.4MPa. The sulfonic groups which were determined by FTIR and SEM were on the membranes. By the investigations of the chemical and thermal stabilization, it was found to be a good stabilization of the PVDF-g-PSSA membranes to acid and organic solvent, and at 40℃-120℃ the capabilities were changed little. These showed that the PVDF-g-PSSA membranes had good chemical and thermal stabilization.After the study of permselectivity of different cations and different concentrations of the sulfonated membranes, the results showed that at the same concentration of the electrolyte, the permselectivity of the higher electrovalent was better than the lower one. With the increasing of the concentration, the permselectivity would decline, and the degrees of declining of different cations were different.