Structure formation and characterization of PVDF hollow fiber membranes by melt-spinning and stretching method

Melt-spinning and stretching (MS-S) method was proposed for preparing poly(vinylidene fluoride) (PVDF) hollow fiber membranes with excellent mechanical properties. The morphology and properties of PVDF fibers and membranes were investigated by small angle X-ray scattering (SAXS), differential scanning calorimeter (DSC), field emission scanning electron microscope, mercury porosimeter, and tensile experiment. SAXS results indicated that the stacked lamellar structure aligned normal to the fiber axis was separated and deformed when the fibers were strained, and the long period of the strained fibers increased accordingly. Factors affecting the membrane properties were mainly spin-draw ratio, annealing temperature, time, and stretching rate. Experimental results showed that the average pore size, porosity, and N-2 permeation of the membranes all increased with the increasing spin-draw ratios and annealing temperatures. Annealing the nascent PVDF hollow fibers at 145 degrees C for 12 h was suitable for attaining membranes with good performance. In addition, the amount and size of the micropores of the membrane increased obviously with stretching rate. Tensile experinlEnt indicated PVDF hollow fiber membranes made by MS-S process had excellent mechanical properties. (c) 2007 Wiley Periodicals, Inc.