Abstract: Porous hollow fibers composed of a high density polyethylene the fibers having rectangular micropores that are oriented in the lengthwise direction of the fibers and having a porosity from 30 to 90% by volume are disclosed. Membranes composed of hollow fibers exhibit a water permeability of greater than 65 (ml/m.sup.2, hr, mmHg) as well as a human serum albumin permeability of greater than 30%. Such fibers are suited for use as filters, particularly as a membrane for simple fractionation of whole blood into it plasma and cellular components. The hollow fibers are obtained by spinning a high-density polyethylene under a high-draft condition followed by cold stretching and hot stretching, and without the use of any solvent or plasticizer.

Abstract: Porous hollow fibers composed of a high density polyethylene the fibers having rectangular micropores that are oriented in the lengthwise direction of the fibers and having a porosity from 30 to 90% by volume are disclosed. Membranes composed of hollow fibers exhibit a water permeability of greater than 65 (ml/m.sup.2, hr, mmHg) as well as a human serum albumin permeability of greater than 30%. Such fibers are suited for use as filters, particularly as a membrane for simple fractionation of whole blood into its plasma and cellular components. The hollow fibers are obtained by spinning a high-density polyethylene under a high-draft condition followed by cold stretching and hot stretching, and without the use of any solvent or plasticizer.

Abstract: A process which comprises allowing a liquid to contact with the inside of a microporous hollow fiber and a fluid to contact with the outside, thereby allowing the gaseous components contained in both fluids to transfer between said liquid and said fluid. For use in the process, the inner diameter of the hollow fiber should be 50 to 5,000.mu. and the wall membrane should have an average micropore diameter of 0.01 to 0.5.mu., a porosity of 10 vol.-% or more, a micropore surface area of 5 m.sup.2 /g or more, and an oxygen permeability of 10.sup.-6 cm.sup.3 (STP).multidot.cm/cm.sup.2 .multidot.sec.multidot.cmHg or more. In cases where the liquid is water or a liquid substance with aqueous medium, the process can be used effectively in artificial lung units or the like by using a hollow fiber of a polyolefin or a fluorinated polyolefin.