Process for preparing microporous polyethylene hollow fibers

Claim 1

A process for preparing a hollow fiber which consists essentially of polyethylene and is a microporous hollow fiber in which the porosity is contiguous and the O 2 gas permeability is at least 2×10 -5 cc (STP) per cm 2 per second per cm Hg transmembrane pressure differential, said process comprising: (a) providing a polyethylene/ester mixture of which about 20 to about 80 weight percent consists essentially of polyethylene and the balance consists essentially of an ester or a mixture of esters, of the formula R 1 (COOR 2 ) n , wherein n is 1 or 2, R 1 is a mono- or divalent hydrocarbon radical, optionally interrupted by one or two --O-- or --S-- links, and containing from 1 to 32 carbons, each R 2 independently is an aliphatic hydrocarbon radical of 2-26 carbon atoms or consists of two aliphatic hydrocarbon moieties joined by an --O-- or --S-- link and containing a total of from 3 to 20 carbons; (b) heating said polyethylene/ester mixture to a temperature at which it is a homogeneous liquid but below the boiling or decomposition temperature thereof, and extruding it from a spinnerette in the form of a hollow fiber; (c) cooling the issuing extrudate to solidify it while maintaining sufficient tension on the forming fiber to achieve a draw ratio of from about 1.0/1 to about 40/1; (d) at a temperature above the melting point of the ester, but at least 10° below the cloud point of said homogeneous liquid, post-spin drawing the solidified fiber under sufficient tension to achieve an overall draw ratio of from about 1.5/1 to about 800/1; and (e) contacting the post-spin drawn fiber with a liquid ester-removal medium, at a temperature intermediate of the freezing point of the medium and the flow point of the polyethylene, until at least a major proportion of the ester is removed from the fiber.