Anion-exchange groups were introduced into an existing microfiltration membrane by radiation-induced grafting and subsequent chemical modification. The tertiary-amino-group-containing monomers, i.e. diethylaminoethyl methacrylate (DEAEMA) and vinyl pyridine (VP), and epoxy-group-containing monomer, i.e. glycidyl methacrylate (GMA), were grafted onto the porous polyethylene hollow-fiber membrane. The epoxy group produced in the GMA-grafted hollow fiber was converted into tertiary amino groups by reaction with diethylamine (DEA) and 4-aminopyridine (AP). Subsequently, the DEA- and AP-modified hollow fibers and the DEAEMA- and VP-grafted hollow fibers were all quaternized with benzyl chloride (BC). Measurements of pure water flux and ion-exchange capacity of the resulting membranes, which contained a strongly basic anion-exchange group, demonstrated that the quaternized membrane (DEA-BC-T fiber) originating from the DEA-modified membrane was the most suitable membrane for anion collection by permeation through its pores. The DEA-BC-T fiber had a pure water flux of 1.0 m/hr at a filtration pressure of 0.1 MPa and an ion-exchange capacity of 1 mol/kg.
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