Ionic Transport Properties of Cation-Exchange Membranes Prepared from Poly(vinyl alcohol-b-sodium Styrene Sulfonate)

Abstract

Membrane resistance and permselectivity for counter-ions have important roles in determining the performance of cation-exchange membranes (CEMs). In this study, PVA-based polyanions—poly(vinyl alcohol-b-sodium styrene sulfonate)—were synthesized, changing the molar percentages C_CEG of the cation-exchange groups with respect to the vinyl alcohol groups. From the block copolymer, poly(vinyl alcohol) (PVA)-based CEMs, hereafter called “B-CEMs”, were prepared by crosslinking the PVA chains with glutaraldehyde (GA) solution at various GA concentrations C_GA. The ionic transport properties of the B-CEMs were compared with those previously reported for the CEMs prepared using a random copolymer—poly(vinyl alcohol-co-2-acrylamido-2-methylpropane sulfonic acid)—hereafter called ”R-CEMs”. The B-CEMs had lower water content than the R-CEMs at equal molar percentages of the cation-exchange groups. The charge density of the B-CEMs increased as C_CEG increased, and reached a maximum value, which increased with increasing C_GA. A maximum charge density of 1.47 mol/dm³ was obtained for a B-CEM with C_CEG = 2.9 mol% and C_GA = 0.10 vol.%, indicating that the B-CEM had almost two-thirds of the permselectivity of a commercial CEM (CMX: ASTOM Corp. Japan). The dynamic transport number and membrane resistance of a B-CEM with C_CEG = 8.3 mol% and C_GA = 0.10 vol.% were 0.99 and 1.6 Ωcm², respectively. The B-CEM showed higher dynamic transport numbers than those of the R-CEMs with similar membrane resistances.