Treatment of synthetic linear polymer filaments and like structures to improved their impact strength and other properties

摘要

549,452. Artificial filaments, racket strings, fabrics, films, &c. DU PONT DE NEMOURS & CO., E. I., and CATLIN, W. E. May 19, 1941, No. 6409. [Classes 2 (ii) and 2 (iii)] Filaments, films, or the like, comprising a synthetic linear condensation polymer of oriented molecular structure, are heated in the presence of a non-solvent swelling agent until the impact strength of the filament or other article has increased at least 25 per cent., but for a shorter period than would cause a decrease in the tensile strength of more than 30 per cent., while permitting substantially free axial shrinkage during the heating. The treatment increases the knotting strength as well as impact strength and increases the general toughness but the tensile strength is decreased and the elongation at break is increased. The treatment should be stopped before the elongation at break has exceeded 50 per cent. The polymer may be a synthetic linear polyamide made from a mono-amino carboxylic acid or an amide forming derivative thereof, e.g. an ester, halide, anhydride, or amide, or made from a diamine and a dicarboxylic acid. The oriented molecular structure of the filaments or other articles may be produced by cold drawing or cold rolling. Filaments may be formed by extrusion of the molten polymer and they may be rapidly cooled or quenched in order to obtain good toughness and pliability. The filaments selected for the shrinking treatment are preferably those which have not been subjected to any previous treatment with dry heat or heat in the absence of a swelling medium. The non-solvent swelling agent may be saturated steam under pressure or it may be hot water. In an example, a polyhexamethylene sebacamide monofil is soaked in water for several days, and then drawn through a die which reduces its diameter to less than half the original value. It is then heated in relaxed condition in an autoclave for 30 minutes in presence of saturated steam at 151-153‹C. The impact strength is doubled. In another example, a polyamide monofil is wrapped in a loose coil so that it can contract freely and is then heated in boiling water. In another example, a monofil of an interpolymer prepared by the condensation polymerization of a mixture of hexamethylene diammonium adipate and sebacate is die-drawn and then treated, while free to contract, with boiling water, or steam at 120-140‹C. and 15- 45 lbs./sq. in. Polyamides prepared from sebacic, adipic, or azelaic acid and hexamethylene diamine, or from 6-aminocaproic or 12- aminostearic acid, may be used. Those with an intrinsic viscosity above 0.6, and a melt viscosity at 285‹C. above 400 poises are preferred. When the filaments are subjected to die-drawing it is preferable to perform the operation in several stages. The process may be applied to filaments made from polyamide compositions containing resins, cellulose derivatives, plasticizers, or pigments. Instead of water or steam, other swelling agents e.g. alcohols, may be used. The process may be applied to monofils, yarns, threads, cords, fabrics, sheets or ribbons. The treated materials may be used for tennis, badminton, or squash racket strings, violin strings, sewing threads, or parachute cloth. Specifications 461,236, 461,237, and 514,821 are referred to.