Effect of glycerol content in cooling bath on performance of poly(ethylene-co-vinyl alcohol) hollow fiber membranes

Poly(ethylene-co-vinyl alcohol) (EVOH) is a copolymer of ethylene and vinyl alcohol with an excellent combination of chemical, thermal and mechanical properties. EVOH hollow fiber membranes were successfully prepared by adding solvent (glycerol) to the cooling water bath in thermally induced phase separation (TIPS) process. The effect of glycerol:water ratio on membrane structures and properties including water permeability, solute rejection, and membrane strength were studied. EVOH crystallization is so slow that glycerol in the quench bath was allowed to flow into the membrane, thereby achieving high porosity at the outer surface. Therefore, adding solvent (glycerol) and increasing its content brings about an increase in the water permeability and a decrease in solute rejection. However, the membrane becomes more symmetric and weaker with increasing glycerol:water ratio due to the higher porosity.