EFFECT OF NONSOLVENTS ON THE MECHANISM OF WET-CASTING MEMBRANE FORMATION FROM EVAL COPOLYMERS

Symmetric and asymmetric, dense or porous ethylene-vinyl alcohol copolymer (EVAL) membranes were prepared by phase inversion from DMSO solvent into nonsolvent coagulation baths varying in the nature of the nonsolvent. It was found that the equilibrium absorption amount of nonsolvent in dense EVAL membranes and the mixing heat of nonsolvent and DMSO could be used as a predictor of membrane structure which is better and simpler than the behavior of the coagulation value, the idea of the solubility parameter and the rate of precipitation. Hence, one can choose the appropriate nonsolvent coagulation bath to control the membrane morphological structure by regulating the relation between polymer and nonsolvent or between solvent and nonsolvent. The results proposed here are believed to be valid also for other systems.