Effect of formation conditions of poly(ethylene-co-vinyl acetate) membrane on the membrane physical structure and pervaporation properties in the recovery of ethyl acetate from aqueous solution

The solution properties, intrinsic viscosity [η] and Huggins constant KH of ethylene-vinyl acetate (EVA) copolymer with 38 wt% vinyl acetate content (EVA38) in solvents of chloroform (CF), 1,2-dichloroethane (DCE) and cyclohexane (CYH) were measured by an Ubbelohode viscometer. The physical structure and pervaporation performances of the EVA membranes cast from different solvents were also investigated by wide-angle X-ray diffraction (WAXD), contact angle, etc. The EVA38 in non-selective solvent CF reveals high [η] and low KH, both chain segments of vinyl acetate and ethylene are expanded in the solutions, and homogeneous distribution in the EVA38 membranes. It results in high pervaporation performance of both separation factor and permeation flux in the recovery of ethyl acetate from aqueous solutions. Oppositely, EVA38 membranes from selective solvents DCE and CYH give low pervaporation performance relatively due to chains aggregation of ethylene segments or vinyl acetate segments in EVA38. The differences of the pervaporation performance and physical structure of EVA38 membranes from different solvents weaken gradually and disappeared finally with increasing the intensity of post-treatment.