Preparation and characterization of poly(ethylene-co-vinyl alcohol) membranes via thermally induced liquid-liquid phase separation

Porous membranes were prepared through the thermally induced phase separation of poly(ethylene-covinyl alcohol) (EVOH)/glycerol mixtures. The binodal temperature and dynamic crystallization temperature were determined by optical microscopy and differential scanning calorimetry measurements, respectively. It was determined experimentally that the liquid-liquid phase boundaries were shifted to higher temperatures when the ethylene content in EVOH increased. For EVOHs with ethylene contents of 32-44 mol %, liquid-liquid phase separation occurred before crystallization. Cellular pores were formed in these membranes. However, only polymer crystallization (solid-liquid phase separation) occurred for EVOH with a 27 mol % ethylene content, and the membrane morphology was the particulate structure. Scanning electron microscopy showed that the sizes of the cellular pores and crystalline particles in the membranes depended on the ethylene content in EVOH, the polymer concentration, and the cooling rate. Furthermore, the tendency of the pore and particle sizes was examined in terms of the solution thermodynamics of the binary mixture and the crystallization kinetics. (C) 2002 Wiley Periodicals, Inc.