The effect of annealing and stretching parameters on the structure and performance of polypropylene hollow fiber membrane

Polypropylene (PP) is a semi-crystalline polymer that widely used as porous membrane material due to its good thermal stability, excellent mechanical properties, and high chemical resistance. In recent years, porous PP membrane was mainly prepared by melt-stretching technique. This technique can produce PP membrane with high mechanical strength and low cost. Melt-stretching consists of four main processes: (a) melt-extrusion process, (b) annealing, (c) stretching, and (d) heat-setting. The parameters of each process are fundamental to determine the structure and performance of the porous PP membrane, thus the selection of appropriate parameters of each process is very important. In this work, the effect of annealing and stretching parameters on the structure and performance of porous PP membrane was investigated. The PP films was were annealed at various temperatures and then stretched under different stretching steps, including cold stretching, hot stretching, and combination of cold and hot stretching. In addition, the stretching ratio was also varied to study its effect to the pore structure and dimensional stabilityof PP membrane.