EFFECTS OF PRETREATMENTS ON MORPHOLOGY AND PERFORMANCE OF CELLULOSE-ACETATE (FORMAMIDE TYPE) MEMBRANES

The effects of thermal shrinkage pretreatment and prepressurization on the morphology and performance of cellulose acetate (Formamide type, CA-F) membranes have been investigated. Membrane morphology was charac terized by changes in pure water permeability constant A and the solut e transport parameter (D(AM)/Kdelta) for sodium chloride. In the shrin kage temperature range 80-85-degrees-C, A and (D(AM)/Kdelta) for NaCl decrease remarkably indicating a steep decrease in the average pore si ze on the membrane surface and an abrupt change in surface morphology of the membrane. While the initial shrinkage temperature does not affe ct the average pore size on the membrane surface obtained ultimately a t a given higher shrinkage temperature, the former has a significant e ffect on the morphology of the porous sublayer underneath the membrane surface. Both A and (D(AM)/Kdelta) decrease with the pressure used in the prepressurization treatment for membranes preshrunk at 80-degrees -C or less; for those preshrunk at higher temperatures, prepressurizat ion treatment has practically no effect on the relative magnitudes of A and (D(AM)/Kdelta).