Anion exchange membranes with interpenetrating network structures were prepared by blending PVA and a polycation, poly (allylamine). The membranes obtained were physically cross-linked by annealing them and chemically cross-linked by reaction with various concentrations of glutaraldehyde (GA) aqueous solutions. The effect of the cross-linking conditions and polycation content on the ionic transport properties through the membranes was investigated. The water content of the membranes increased with increasing polycation content and with decreasing GA concentration, CGA. The effective charge density of the membranes increased with increasing polycation content, Cpc. The highest value of the effective charge density was 0.78mol dm–3 at the membrane of Cpc=20wt.% and CGA=0.10vol.%. The electric resistance of the membranes also depended on polycation content and GA concentration. The membrane of Cpc=20wt.% and CGA=0.01vol.% had the lowest membrane resistance (1.23Ωcm2) of all the membranes. The dynamic transport number of the membranes increased with increasing polycation content and with increasing GA concentration while the membrane resistance also increased with increasing GA concentration. These results indicate that the ion transport properties of the PVA-based anion exchange membranes can be controlled by changing the polycation content and the cross-linking conditions.
Glycidyl methacrylate (GMA), an epoxy-group-containing monomer, was graft-polymerized onto a high-density polyethylene (HDPE) film with a thickness of 35μm. Divinyl benzene (DVB) was co-grafted as a cross-linker. Toluene used as a solvent of a mixture of GMA and DVB provided a uniform density of the grafted polymer chain across the membrane. Subsequently, the produced epoxy group was converted into anion and cation-exchange groups by a reaction with trimethylammonium chloride and sodium sulfite, respectively. The resultant anion- and cation- exchange membranes exhibited 0.55 and 0.34Ωcm2, respectively, which were lower membrane resistances with ion-exchange capacity comparable to commercially available ion-exchange membranes. The highest brine concentration of 3.7mol/L for electrodialysis of 0.50mol/L sodium chloride as a model seawater was attained using the ion-exchange membranes prepared from GMA/DVB-co-grafted membranes with a DVB mole percentage of 1.0mol%.