The effect of dope solution characteristics on the membrane morphology andgas transport properties: PES/gamma-BL/NMP system

The effect of heterogeneity of a dope polymer solution on membrane morpholo gy has been investigated. Heterogeneity was developed in polyethersulfone s olutions of either gamma-butyrolactone (gamma-BL) or a mixed solvent of gam ma-BL/N-methyl-2-pyrrolidone, which exhibit gelation and/or phase separatio n with aging time. Two different processes for membrane preparation have be en employed; Process I, heterogeneity-developed dope solution was cast on a glass plate with a knife for uniform thickness, and immediately immersed i nto a nonsolvent form of the membrane. Process LI, a dope solution was cast on a glass plate and then aged in a closed environment. After a certain ag ing time, it was immersed into a nonsolvent to be coagulated. The developed heterogeneity was destroyed markedly during casting in Process I, whereas the heterogeneity was maintained until the moment of immersion into a coagu lation medium in Process II. Membranes prepared by Process I were finger-li ke regardless of the aging time, whereas Process II yielded macrovoid-free and sponge-like membranes having enhanced gas permeance and mechanical stre ngth at long aging times. From these results, it was concluded that the mor phology and transport properties of a membrane were able to be controlled b y the solution structure, in particular, the solution heterogeneity in the cast film. (C) 1999 Elsevier Science B.V. All rights reserved.