NOVEL ION-EXCHANGE MEMBRANES FOR ELECTRODIALYSIS PREPARED BY RADIATION-INDUCED GRAFT-POLYMERIZATION

Novel ion-exchange membranes containing sulfonic acid (SO3H) and trimethyl ammonium [N(CH3)(3)] groups were prepared by a simple method of radiation-induced cografting of sodium styrenesulfonate (SSS) with acrylic acid (AAc) and vinyl benzyl trimethyl ammonium chloride (VBTAC) with 2-hydroxyethyl methacrylate (HEMA), onto a polyethylene film with a thickness of 50 mu m. The high density graft chain was introduced throughout the polyethylene film. The maximum cation- and anion-exchange capacities of the resultant membranes were 2.5 and 1.3 mol/kg, respectively. These membranes exhibited an electrical resistance one order lower than commercially available ion-exchange membranes; for example, 12 h cografting provided cation- and anion-exchange membranes whose electrical resistances in a 0.5 M NaCl solution were 0.25 and 0.85 Omega cm(2) respectively. From the evaluation of electrodialytic desalination in a batch mode, using a pair of the graft-type ion-exchange membranes, the time required to achieve 99.5% desalination of the initial 0.5 M NaCl solution was reduced to 85% comparing with that of the commercial ion-exchange membranes.