Ion exchange of lysozyme during permeation across a microporous sulfopropyl-group-containing hollow fiber

A microporous hollow fiber containing a sulfopropyl (SP) group as a strongly acidic cation-exchange group was prepared by radiation-induced graft polymerization of glycidyl methacrylate, followed by hydrolysis of the resulting epoxide group into a diol, and then conversion of the diol into the SP group. The SP group density of the resulting hollow fiber ranged from 0.21 to 0.84 mol/kg of dry fiber with a pure water flux of 2.7 m/h at a filtration pressure of 0.1 MPa. Lysozyme adsorption was examined during permeation of the lysozyme solution (pH 6) through the pores across a microporous cation-exchange hollow fiber. The lysozyme concentration of the effluent penetrating the outside of the hollow fiber did not change irrespective of the residence time of the solution across the hollow fiber, which was indicative of the negligible diffusional resistance of lysozyme to the SP group. The binding capacity of lysozyme to the fiber was constant in this range of SP group density. For comparison, the adsorption characteristics of a cupric chloride solution during permeation were also determined. The binding capacity of Cu to the fiber increased linearly with increasing SP group density, because cupric ions of a smaller size than lysozyme can invade the depths of the grafted polymer branches formed in the amorphous domain of the polymer matrix.