GB682412A - Improvements in or relating to the stretching of filaments, yarns, films and similar shaped articles comprising acrylonitrile polymers - Google Patents

Abstract

<PICT:0682412/IV (a)/1> Filaments, yarns, films and similar articles are formed from a solution of an acrylonitrile polymer containing at least 75 per cent by weight of acrylonitrile in the polymer molecule, and, after treating the articles to reduce the amount of solvent carried thereby to between 0 and 1.5 per cent by weight, the articles are stretched while heated at a temperature of at least 100 DEG C. When the proportion of residual solvent is reduced to the specified range, the articles may be stretched to a higher degree without rupture than when the proportion of solvent is higher. Articles of greater tenacity are obtained. The polymer may be a simple acrylonitrile polymer or it may be a copolymer of acrylonitrile and vinyl acetate, vinyl chloride, 2-vinyl pyridine, acrylic acid or its esters or homologues, styrene, isobutylene, or butadiene. The acrylonitrile polymer may have a molecular weight of 10,000-750,000 or higher. The residual solvent may be reduced to the specified range by washing with water, ethanol, isopropanol, glycerol, or ethylene glycol. Yarns may be washed while travelling in a long length or while wound on bobbins. Wet-spun yarn may be washed in the gel state or after being dried. The washing treatment may require several hours or only a few minutes according to the temperature of the washing-liquid. If desired, the residual solvent may be reduced by evaporation. The spinning solution may contain dimethyl formamide or a mixture of nitromethane with formamide, formic acid, dichloracetic acid, or cyanacetic acid as solvent for the polymer. When the yarns or other articles are made by wet coagulation methods, the coagulating liquid may be water, glycerol, alcohol, ether or an aqueous solution of a salt, an alkali, or an acid. As shown, acrylonitrile polymer yarn 2 proceeds from the coagulating bath 3 to a pair of mutually inclined rolls 4, 5, round which it passes in a series of helical turns. The yarn passes to another pair of rolls 6, 7, which are partially submerged in washing-liquid in vessel 8. The yarn is stretched between the two pairs of rolls. From rolls 6, 7 the yarn proceeds to rolls 9, 10 which are partially immersed in water at 100 DEG C. in vessel 11. The residual solvent is thereby reduced to not more than 1.5 per cent. The washed yarn is passed to a heat-stretching zone. It travels over steam-heated rolls 12, 13, and then through a heated tube 15 to a godet 14, stretching taking place between the rolls and the godet. During the stretching, the yarn may be subjected to dry heat, wet steam, saturated steam, or superheated steam. Specifications 579,887, 595,044 to 595,054, and 603,873 are referred to.