Preparation Of PVDF Hollow Fiber Ultrafiltration Membrane Via Modified TIPS Method And Its Anti-pollution Properties

Polyvinylidene fluoride(PVDF) is one of the widely used membrane materials, dueto good mechanical strength, chemical stability, radiation and heat resistance. In order toobtain a microporous membrane with good permeation, mechanical strengh and porosity,modified TIPS process assisted with NIPS have been applied for membrane preparationIn this Paper,we aimed at studying the influences of various technical conditions onphase separation behaviors and membrane structures during PVDF membarne formationby the TIPS method. The PVDF membrane formation mechnaism was suggested.Therelations of technical conditions, phase separation behaviors and membrane structureswere obtained.The results showed that:(1) With the increase of the solvent concentration in borefluid, the number of the inner surface pores,the water flux and porosity increased.Whenthe TEP is20vt%in the bore fluid,the water flux and the porosity can reach437.37L/（m2·h）and72%, repectively.(2) With the increase of the solvent concentration in thecoagulation bath, the number of the outter surface proes also increase, and the porediameter become bigger, therefore increased the pure water flux and the porousity of themembrane,and the maximum reach537.41L/（m2·h）and74%, repectively. But thecorresponding intercept rate and the mechanical strength decreased quickly.(3)Appropriate drawing rate can strengthen the mechanical strength; When the feed rate ofthe dope solution was determined, the porosity and the pure water flux of the membraneis proportional to the drawing rate. With the increase of the drawing rate,the mechanicalstrength of the membrane fibre firstly increased, and then decreased to some extent, the spinning process could be interrupted.(4)The high air gap would result to theevaporation of the solvent on the out-surface of the membrane. The PVDFconcentration on the outter surface get higher, consequently, resulting in the formationof a denser layer. The higher air gap is, the more denser the layer is, which greatlyenhanced the interception of the membrane.The results show that, with the increase of the solvent concentration in the borefluid and the coagulation bath, the number of the membrane pores, the pore size,thepure water flux and the porosity would increase. And, the rising air gap is a favor ofincreasing the mechanical strength of the membrane.When the concentration of the TEPin the bore fluid is20%(vt%), the casting membrane solution temperature is120℃,theair gap is1㎝, the coagulation bath temperature is60%(wt%) TEP water solution at20℃, the drawing rate is0.75, the membrane had good structure and properties.