Preparation of Porous PTFE Hollow Fiber Membranes Through Mechanical Operations

Porous polytetrafluoroethylene (PTFE) hollow fiber membranes were prepared from fine powder through a series of mechanical operations. The morphological structures of the prepared hollow fiber membrane were well analyzed by SEM, which were characterized by a spatial periodicity of node (domain of agglomerated PTFE particles) and fibril domains. The fibrils were highly oriented in the direction of the stretching operation, providing pores in the polymeric membrane as split-like voids between adjoining fibrils. The unit size of the periodic structure varied depending on the heat-treatment, stretching and sintering conditions. The property of primary PTFE fiber was changed by heating temperature, the PTFE membrane porous and morphological structures were significantly changed by stretching rate, stretching ratio, and sintering temperature. It was found that heat-treatment process could improve mechanical strength of primary PTFE fiber, and benefit for the forming and growth of fibrils. Remarkably, the higher stretching rate tended to result in smaller pore size and narrower pore size distribution, the higher stretching ratio increased porosity and enlarged pore size. Simultaneously, the shrinkage ratio decreased with the increase in the sintering temperature, and became constant at around 2.5% above 330°C. According to the results, it is indicated that mechanical operation is feasible to gain excellent porous PTFE hollow fiber membrane.