IMPROVEMENTS IN OR RELATING TO SYNTHETIC POLYMER FILAMENT

摘要

1414652 Acrylonitrile polymer filaments E I DU PONT DE NEMOURS & CO 16 Oct 1972 [14 Oct 1971] 27906/75 Divided out of 1414651 Heading B5B [Also in Division C3] Filaments of acrylonitrile polymers containing 80-100% by weight acrylonitrile units and 0-20% by weight of units of one or more comonomers have a sheath extending inward from the surface of the filament with a thickness of from 5 to 50% of the distance from the outer surface of the filament to the central axis of the filament, the sheath having a positive density gradient wherein the highest density is at or near the surface of the filament and having substantially no optical voids. The exemplified comonomer units are derived from one or more of methyl acrylate, sodium styrene sulphonate, styrene, ethylene, 2-methyl-5-vinylpyridine and vinyl acetate. The filaments are produced by extruding a composition containing the acrylonitrile polymer and water, wherein the water is present, completely or partially, in the form of a hydrate with the nitrile groups of the polymer, through an orifice at a temperature of from 25‹ C. below to 10‹ C. above the temperature of hydration of the acrylonitrile polymer). (The hydrated polymer compositions are described and claimed in Specification 1,414,651. The extruded filaments comprise a core containing voids having lateral diameters of from 0À05 to 1 micron in a concentration of between 105 and 107/mm.2 of core cross-section. When the filaments are drawn, e.g. to 200% or more of their as-spun length, the sheath develops discrete, longitudinal striations on the outer surface or skin and the voids in the core are elongated and reduced in diameter, the drawn filaments thereby developing a positive form birefringence. If the filaments are heated, the core voids can be reduced to less than 0À05 micron in diameter and the birefringence disappears.