Porous water filtration membrane of vinylidene fluoride resin hollow fiber and process for production thereof

Abstract

A composition is formed by blending a vinylidene fluoride resin having a relatively high molecular weight and an improved crystallinity represented by a difference Tm−Tc of at most 32° C. between an inherent melting point Tmand a crystallization temperature Tc of the resin with a plasticizer and a good solvent for vinylidene fluoride resin, and the composition is melt-extruded into a hollow fiber-form. The hollow fiber-form extrudate is then cooled to be solidified from an outside thereof by introduction into cooling medium and subjected to extraction of the plasticizer and stretching, thereby forming a hollow fiber porous membrane of vinylidene fluoride resin characterized by co-presence of crystal oriented portion and crystal non-oriented portion recognizable by X-ray diffraction method. The resultant hollow fiber porous membrane of vinylidene fluoride resin has micro-pores of appropriate size and distribution, is excellent in mechanical strength represented by tensile strength and elongation at break and is useful as a water microfiltration membrane.