THE INFLUENCE OF PEG MOLECULAR WEIGHT ON MORPHOLOGIES AND PROPERTIES OF PVDF ASYMMETRIC MEMBRANES

<正>The preparation and properties of asymmetric poly(vinyldiene fluoride)(PVDF)membranes are described in this study.Membranes were prepared from a casting solution of PVDF,N,N-dimethylacetamide(DMAc)solvent and water- soluble poly(ethylene glycol)(PEG)additives by immersing them in water as coagulant medium.Experiments showed that when PEG molecular weight increased,the changes in the resultant membranes' morphologies and properties showed a transition point at PEG6000.This indicated that PEG with a relatively low molecular weight was used as a pore-forming agent to enhance pure water flux and reduce solute rejection of membranes,but PEG was used as a pore-reducing agent with a further increment of PEG molecular weight to result in pure water flux decreasing and solute rejection increasing.Finally, combined with the precipitation rates of different membrane-forming systems,the membrane formation mechanism describing PEG mobility was discussed extensively basing on the length changes of PEG molecular chains and the affinity between PEG and casting solution.The results offered a better understanding of effects of PEG additives on membrane structure and properties.