GB585367A - Production of an improved acrylonitrile polymer yarn - Google Patents

Abstract

<PICT:0585367/IV/1> An acrylonitrile polymer yarn, film, tubing, fibre, or similar article which has been treated, e.g. stretched so that it has a pronounced oriented micellar structure is heated in relaxed state to a temperature of at least 80 DEG C. until it has substantially ceased to shrink and is then maintained at a temperature of at least 80 DEG C. for 1 to 24 hours in relaxed state or under such a p low tension that there is substantially no stretching. The heat treatment may be effected in air or in an atmosphere of an inert gas or in an inert liquid. The treatment improves the tenacity and elongation of the yarn or other article. The degree of orientation of the yarn to be treated is at least equal to that obtained by stretching a dry spun yarn of the polymer and subsequently stretching it to twice its original length while passing through glycerol at 130 DEG C. The initial heating in relaxed state causes the yarn to shrink 10-25 per cent of its length. The second step involving a prolonged heating of the shrunken yarn produces an increase in tenancity without loss of elongation. The acrylonitrile polymer may have a molecular weight of 7,000 to 400,000. It may be a simple polymer or an interpolymer of acrylonitrile and a vinyl compound, an olefinic compound, or an unsaturated carboxylic acid, provided that such an interpolymer contains a major portion of acrylonitrile As shown in Fig. 1, the acrylonitrile polymer yarn 1 is unwound at constant weight from bobbin 2 by roller 3 and is led through the heating device 5 by roller 6. The roller speeds are adjusted to that the yarn is heated in relaxed state. The yarn is wound on to a bobbin under low tension and the wound package is placed in an oven at 80 DEG C. or more for at least 1 hour. As shown in Fig. 2, the heating device comprises a solid block provided with a slot 21 through which the yarn 1 is led and a bore 22 in which is placed an electrical resistance 23. In an example, a solution of acrylonitrile polymer in tetramethylene cyclic sulphone is dry spun and the yarn obtained is stretched between rollers and while passing over a heated pin to 8 times its original length. The yarn is then passed through a slot in a heated metal block while free to shrink, and after collection under low tension on a bobbin it is heated at 150 DEG C. for 1 hour. In another example, a solution of acrylonitrile polymer in dimethyl formamide is extruded into hot glycerine. The yarn obtained is wound into skeins and suspended in relaxed condition for at least 1 hour in glycerine at 100 DEG C. Specifications 579,887, 583,939 and 585,368 are referred to.