Preparation And Characterization Of The PVDF/Polystyrene Cation Exchange Alloy Membranes

On the basis of state existing ion exchange resin industries as well as the traditional heterogeneous ion exchange membrane production processes, we proposed a novel route for manufacturing the poly(vinylidene fluoride)/polystyrene (PVDF/PSt) cation exchange alloy membrane with a structure of semi-interpenetrating network. The properties of alloy membrane (including the ion exchange capacity, water content, areal electrical resistance, transport number, salt diffusion coefficient, bursting strength and dimensional stability) were measured. The effects of the polystyrene-divinylbenzene (DVB) to PVDF mass ratio (RSt-DVB/PVDF) and the DVB content in the monomers on the physical and electrochemical properties of the prepared alloy membranes were investigated. Moreover, the actually performances of the alloy membranes in the electrodialysis were also operated and evaluated.The cation exchange alloy particles were prepared by the sulfonation of semi-interpenetrating polymer alloy particles which were manufactured by solution polymerization method using PVDF as matrix material and styrene-DVB as monomers. From the FTIR spectra, the group feature peaks respectively observed at1128and1009cm-1, as well as the S=O stretching vibration at1039cm-1, were all indicating the successful introduction of sulfonic acid groups into the polymer alloy particles. Moreover, the degree of sulfonation decreased with the increase of DVB content, and the pre-swelling of alloy particles in the1,2-dichloroethane before the sulfonation functioned well on facilitating the sulfonation efficiency.Employing the classical method similar to the manufacturing of heterogeneous cation exchange membranes, the cation exchange alloy powders were hot pressed to form the alloy membranes after pulverization, mixing and open milling. The SEM photos of resulting alloy membranes showed a uniform distribution of functional group regions in the membrane matrix, and with the increase of DVB content, the membrane structure became more dense. The optimal resulting membranes possessed the area electrical resistance values within a range of3.0-6.6O·cm2, the desirable permselectivity higher than90%and the low salt diffusion coefficient which was attributing to the dense membrane structure. Besides, the alloy membranes exhibited fine bursting strengthen about0.60MPa and excellent dimensional stability without the reinforcing fabrics. All the results illustrated that the properties of lab-made alloy membranes were obviously superior to commercial heterogeneous cation exchange membranes, and were approached to the homogeneous membranes.