Poly（vinylidene fluoride）(PVDF) was prepared for the ultrafiltration membranes because of its good film forming ability, high mechanical strength, and chemical resistance to solvents. Membranes were prepared by solvent casting method on a glass plate. To investigate the effect of casting solvents on the membrane performances dimethyl formamide(DMF), dimethyl sulfoxide(DMSO), and dimethyl acetamide(DMAc) were used as casting solvents. The solvent composition of casting solution was selected from one of followings; (A) homosolvent system of DMF, DMSO or DMAc, (B) binary solvent system of DMSO/DMF, DMF/DMAc or DMAc/DMSO, and (C) binary solvent system of solvent and volatile nonsolvent such as acetone.
Ultrafiltration experments were carried out with 0.2 % aqueous solution of polyethylene glycol（PEG, average molecular weight of 1,500-20,000）. Water flux and rejection were measured, and the cross-sectional structures of membranes were observed by a scanning electron microscope. From the result of water permeation, it was revealed that most of all the PVDF membranes had the water flux 10∼200(ℓ/㎡·hr) at 2 atm. Membranes prepared by DMF solvent DMF solvent system had the high rejection values inspite of poor water fluxes in comparison with other membranes. DMAC and DMF solvent systems showed the sharp slope of rejection curves with the increase of molecular weight of solute, and especially, membranes prepared by DMSO had good performances for ultrafiltration.