Porous PVDF asymmetric hollow fiber membranes prepared with the use of small molecular additives

Preparation of polyvinylidene fluoride (PVDF) asymmetric hollow fiber membr anes was studied by introducing small molecular additives, which include no nsolvents (water, ethanol and 1-propanol) and inorganic salt (LiCl). Dimeth ylacetamide (DMAC) was used as a solvent. Water was used as an external coa gulant, while water, ethanol or a mixture of water and ethanol was used as an internal coagulant. The prepared PVDF hollow fiber membranes were charac terized in terms of water flux, and molecular weight cut-off for the wet me mbranes. Average pore size and effective surface porosity were determined u sing the gas permeation method for the dried membranes. The cross-sectional structure of the hallow fibers was examined by scanning electron microscop y. The collapsing pressure and wetting pressure of the dried membranes were also tested. The effect of polymer concentration, non-solvents, the mixtur e of non-solvent and LiCl. internal coagulant and post-treatment was studie d in details. The PVDF hollow fibers prepared from the small molecular addi tives exhibit good mechanical strength and excellent hydophobicity. The PVD F hollow fiber spun from the non-solvent alone exhibits a quite low permeab ility, while good PVDF porous hollow fiber membranes were prepared using a mixture of the water/LiCl, or 1-propanol/LiCl as the additive. (C) 2000 Els evier Science B.V. All rights reserved.