CHARACTERIZATION OF REVERSE-OSMOSIS CELLULOSE-ACETATE MEMBRANES BY GAS-ADSORPTION METHOD - EFFECT OF CASTING VARIABLES AND CHLORINE DAMAGE

The gas adsorption isotherms of cellulose acetate RO membranes were investigated in order to characterize the pores of laboratory prepared membranes. The data showed that before annealing, the molecular structure was relatively homogeneous, but during annealing, the heterogeneity of the membrane molecular structure increased, the micropores were enlarged and thus pore volume and surface area were increased. The nature of the membrane pore structure suggested by adsorption measurements on vacuum dried RO membranes will not, however, be identical to that existing before membrane drying. The water permeability decreased from 278.0 X 10(-5) cm3/cm2-sec for unannealed membrane to 9.2 X 10(-5) cm3/cm2-sec for membranes annealed at 90-degrees-C. Increase of gelation temperature made the resulting membrane possess mesopores in spite of unannealed conditions. The membrane gelation temperature of 20-degrees-C showed the characteristics of an ultra-filtration membrane. Gas adsorption experiments using chlorine damaged membranes showed considerable decrease in both pore volume and surface area.