EFFECT OF COAGULATION CONDITIONS ON STRUCTURE AND PROPERTIES OF MEMBRANES FROM ALIPHATIC POLYAMIDES

Polyamide membranes were cast by phase inversion from a protic solvent into coagulation baths varying in composition. The coagulants were classified by a ''coagulation value'', obtained in separate titration experiments. The morphology of the top layer (skin) and cross-section (sublayer) of each membrane was determined by scanning electron microscopy. It was found that the coagulation value could be used as a prediction of membrane structure, which could also be correlated to performance. By increasing ammonia in the coagulation bath the membranes produced changed from sponge-structured microfilters to finger-structured ultrafilters. The movement of the coagulation front during membrane formation was measured by a video-microscopic technique, where thin sandwiched layers of dope were exposed to a coagulant environment, and the kinetics were found to follow Fickian diffusion behaviour.