| abstract |
Disclosed is a porous polypropylene hollow fiber membrane of large pore diameter which have (a) rectangular pores formed by microfibrils that are oriented in the lengthwise direction of the fibers and joint portions that are composed of stacked lamellae, the pores being contiguous with each other from the inner wall surface to the outer wall surface of the hollow fiber membrane to form a stacked, multicellular structure, (b) an average pore diameter ranging from 1.7 mu m up to 10 mu m as measured with a mercury porosimeter, (c) a porosity of 80 to 95%, and (d) an air permeability of not less than 4x105 l/m2.hr.0.5 atm. This hollow fiber membrane can be produced by melt-spinning polypropylene, annealing the resulting unstretched hollow fiber under specific conditions, and then cold-stretching and hot-stretching the annealed hollow fiber under specific conditions. |