Polymer Engineering and Science, Vol.48, No.5, 934-940, 2008
Effect of hot-press on electrospun poly(vinylidene fluoride) membranes
Poly(vinylidene fluoride) (PVDF) was electrospun into ultrafine fibrous membranes from its solutions in a mixture of N,N-dimethylformamide and acetone (91, v/v). The electrospun membranes were subsequently treated by continuous hot-press at elevated temperatures up to 155 degrees C. Changes of morphology, crystallinity, porosity, liquid absorption, and mechanical properties of the membranes after hot-press were investigated. Results of scanning electron microscopy showed that there were no significant changes in fibrous membrane morphology when the hot-press temperature varied from room temperature to 130 degrees C, but larger pores were formed because of fibers melting and bonding under higher temperatures. Analyses of X-ray diffraction and differential scanning calorimeter exhibited that the crystalline form of PVDF could transfer from P-type to oe-type during hot-press at temperatures higher than 65 degrees C. Tensile tests suggested that the mechanical properties of the electrospun PVDF membranes were remarkably enhanced from 25 to 130 degrees C, whereas the porosity and the liquid absorption decreased. The hotpress at 130 degrees C was optimal for the electrospun PVDF membranes. The continuous hot-press post-treatment could be a feasible method to produce electrospun membranes, not limited to PVDF, with suitable mechanical properties as well as good porosity and liquid absorption for their applications in high-quality filtrations or battery separators.