Novel Ion‐Exchange Membranes for Electrodialysis Prepared by Radiation‐Induced Graft Polymerization

Novel ion‐exchange membranes containing sulfonic acid and trimethyl ammonium 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 μm. 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 solution were 0.25 and 0.85 Ω cm², 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 solution was reduced to 85% comparing with that of the commercial ion‐exchange membranes.