Structure and Properties of PVDF Hollow Fiber Membranes Made by Melt-Spinning and Stretching Process

摘要

Poly(vinylidene fluoride)(PVDF) is one of the widely used fluoride-containing membrane materials, due to its excellent processability, chemical resistance and good thermal property. PVDF membranes were usually prepared by two methods: thermally induced phase separation (TIPS) and solution phase inversion methods . However, the above two methods all can result in a waste solvent problem and the mechanical properties of the membranes made by these methods were relative poor. So a new method such as melt-spinning and stretching (MS-S) process should be developed to prepare PVDF membranes with excellent mechanical properties. The micropore formation mechanism by MS-S method is due to the stacked crystalline lamellae which are aligned normal to the extrusion direction. When stretched, the crystalline lamellae will be separated with large number of voids forming, and the voids are interconnected. Thus, the micropore structure is formed by the stress and then it is completed during annealing . This means that the MS-S process does not involve any phase separation and its handling is relatively easy. In our knowledge, PVDF hollow fiber membranes made by MS-S method have not been reported. In the present paper, PVDF hollow fiber membranes were prepared by MS-S process. Tensile experiment showed that the membranes had excellent mechanical properties. The effects of melt-spinning and stretching conditions such as spin-draw ratio, annealing and stretching rate on the structure and properties of PVDF hollow membranes are also discussed.