2003 Volume 57 Issue 6 Pages 498-507
The chlorine resistance of reverse osmosis membranes was investigated with a cross-linked aromatic polyamide composite membrane, an N-substituted polyamide composite, and a cellulose acetate asymmetric. The degradation was observed as the increase in both solute and water permeation coefficients, which can be expressed as functions of a quantity of chlorine concentration to the Xth power times the chlorine exposure time. It was found that values of X are in the range of 0.5-0.7 for the cross-linked aromatic polyamide composite, 1.2 for the N-substituted polyamide composite, and 1.5 for the cellulose acetate asymmetric. The value of X seems closely related to the degradation mechanism. In the case of rapid degradation, the degradation might be mainly caused by chlorination, and the value of X should be close to 0.5. On the other hand, in the case of slow degradation, the degradation might be mainly caused by oxidation, and the value of X should be close to 2. The morphological and structural changes due to the chlorination degradation were observed using electron microscopy and ESCA, and the membrane transport characteristic change was discussed from the observed results such as membrane thickness, its looseness, and its fixed charge density.
