Cation-Exchange Porous Hollow-Fiber Membranes Prepared by Radiation-Induced Cografting of GMA and EDMA Which Improved Pure Water Permeability and Sodium Ion Adsorptivity

Strongly acidic cation-exchange porous hollow-fiber membranes with a high water permeability and a high affinity for sodium ion were prepared. Cross-linked polymer chains, consisting of ethylene dimethacrylate (EDMA) as a cross-linker and glycidyl methacrylate (GMA) as a precursor monomer for sulfonation, were appended onto a porous hollow-fiber membrane by radiation-induced graft polymerization. The degree of cross-linking, which is defined by the molar content of EDMA in a monomer solution of EDMA and GMA, ranged from 3 to 12%. For example, the cation-exchange membrane immobilizing un-cross-linked graft chains exhibited a negligible pure water flux, whereas that immobilizing cross-linked graft chains with a degree of cross-linking of 6% had a 1.2-fold higher pure water flux than the original hollow-fiber membrane. Sodium ions were captured during the permeation of the sodium chloride solution through the cation-exchange membranes. The capturing efficiency for sodium ion, which is defined as the ratio of breakthrough capacity to equilibrium capacity, increased with an increase in the degree of cross-linking.