Effect of annealing on the morphology of porous polypropylene hollow fiber membranes

Three different polypropylene resins were selected to develop microporous membranes through melt spinning, annealing and stretching. The effects of take-up speed, cooling rate, stretching, and annealing temperature on the crystalline structure and orientation of the membrane were investigated using field emission scanning electron microscopy. An annealing process was employed to generate and enlarge the pores and lamellar structure, and improved the crystallinity of hollow fiber precursors, before the stretching process. The annealed hollow fiber precursor was stretched by cold, hot, and cold/hot complex stretching. We observed that porous structure on the outer and inner surfaces of the stretched precursor fibers were produced by cold and hot complex stretching.