Preparation And Properties Of EVOH Ultrafiltration Membrane Via Combining TIPS With Pre-evaporation

Poly?ethylene-co-vinyl alcohol??EVOH?is a crystalline randomco polymer with vinyl alcohol and ethylene segments,where vinyl alcohol segment brings better hydrophilicity and ethylene segment brings better mechanical strength.As a result,the EVOH membrane attracts extensive attention.In this paper,the EVOH/sulfolane/1,3-propanediol ternary system phase diagram was obtained by theoretical calculation method and experimental determination one,which provided theoretical support for the preparation of EVOH ultrafiltration membrane.For the EVOH/sulfolane/1,3-propanediol ternary system,the calculated solid-liquid phase separation curves agree well with dynamic crystallization point measured by experiment.However,there is a certain deviation between the calculated liquid-liquid phase separation curves and the measured cloud point data,but the overall change trend is consistent,which does not affect the qualitative analysis of the phase separation behavior of the system.EVOH ultrafiltration membrane was prepared via conventional TIPS method and combining TIPS with pre-evaporation,using a novel co-solvent that is a mixture of sulfolane and 1,3-propanediol.In the conventional TIPS process,when the rejection performance of the ultrafiltration membrane was improved by increasing the polymer concentration or reducing the cooling rate,it was always accompanied by a serious decrease in permeability.In the combining TIPS with pre-evaporation process,the rejection performance of the ultrafiltration membrane was improved via pre-evaporation method,which could minimize the damage to permeability.As a result,an asymmetric ultrafiltration membrane with high flux and high rejection performance was obtained.In the experimental range,with the increase of pre-evaporation time,the compactness of the dense layer increased first and then decreased.Correspondingly,the rejection rate of the EVOH ultrafiltration membrane to the BSA increased first and then decreased.When the pre-evaporation time is 20s,the compactness of the dense layer was the best.The EVOH ultrafiltration membrane had the highest rejection rate to BSA,reaching 98%.The pure water flux at this time was 301.62L·m^-2·h^-1·bar^-1.The rejection rate of EVOH ultrafiltration membrane to BSA increased first and then decreased with the increase of pre-evaporation temperature.When the pre-evaporation temperature was 50°C,the rejection rate of EVOH ultrafiltration membrane to BSA was the highest,reaching 99%,and the pure water flux was 137.1 L·m^-2·h^-1·bar^-1.Finally,the effects of co-solvent ratio on membrane structure and properties were studied when the pre-evaporation temperature was room temperature and the pre-evaporation time was 20 s.The results showed that both the rejection of BSA and the pure water flux increased first and then decreased with the increase of1,3-propanediol content in the cosolvent.