Effect of hot‐press on electrospun poly(vinylidene fluoride) membranes

Abstract

Poly(vinylidene fluoride) (PVDF) was electrospun into ultrafine fibrous membranes from its solutions in a mixture of N,N‐dimethylformamide and acetone (9:1, v/v). The electrospun membranes were subsequently treated by continuous hot‐press at elevated temperatures up to 155°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°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 β‐type to α‐type during hot‐press at temperatures higher than 65°C. Tensile tests suggested that the mechanical properties of the electrospun PVDF membranes were remarkably enhanced from 25 to 130°C, whereas the porosity and the liquid absorption decreased. The hot‐press at 130°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. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Improving Nanofiber Membrane Characteristics and Membrane Distillation Performance of Heat-Pressed Membranes via Annealing Post-Treatment

“…After the neat membrane was heat-pressed, the band at 840 cm −1 representing the β phase increased from 53% to 63.6%, while the band in terms of the α phase did not appear after the heat-press treatment. The increase in the transmittance of β phase bands indicated the increase in the crystallinity of the membrane as the amorphous phase of the PVDF was converted into the β phase due to the mechanical deformation, caused by the pressure applied on the membranes during heat-pressing [25,26]. Vineet et al found that annealing PVDF …”

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