The Effect of Stretch on Multi-Pore-Structure of Ultrahigh Molecular Weight Polyethylene/SiO 2 Hybrid Hollow Fiber Membranes

Abstract

Ultrahigh molecular weight polyethylene/SiO2 hybrid hollow fiber membranes were prepared by thermally induced phase separation (TIPS), using mineral oil as the diluent and SiO2 as the additive. The influences of heat-treatment, drawing ratio and drawing temperature on melting behavior, crystallization, multi-pore-structure (MPS) and porosity were investigated. The results of this study demonstrated that the original crystal grains became more perfect and that new micro crystallites were produced through heat treatment. Defects were more easily formed by the micro crystallites in cold stretching. Heat treatment also made the pores contract. The MPS including TIPS pore, stretching pore and interfacial microvoid was constructed after stretching. A model of interfacial microvoid was built. The model indicated that the area of interfacial microvoid increased as the drawing ratio became larger, reaching a maximum at a certain drawing ratio. Values above this maximum drawing ratio made no contribution to further increase the triangular area of interfacial microvoid but made many TIPS pores close. As the drawing ratio increased, the pore diameter ( PD) and total pore fraction ( TPF ) of the stretched pores increased whereas the TPF of the TIPS pores decreased. The pore diameter distribution ( PDD) and the porosity resulted from the joint effect of multiple pores. Without stretching, the porosity was slight due to the pores contracting, and it increased as the drawing ratio became larger, reaching a maximum at a drawing ratio of 5 times.