GB748504A - Improvements in or relating to the production of polyacrylonitrile filaments and films - Google Patents

Abstract

Filaments or films are formed by spinning or extruding an aqueous saline solution of a polymer containing at least 85 per cent of acrylonitrile in the polymer molecule into a coagulating bath consisting of an aqueous solution of one or more salts which is at a concentration of 0.33 to 0.67 times that of the salt or salts in the polymer solution when the concentration of the salt or salts in the polymer solution is over 60 per cent, and from over 0.67 to 0.9 times the concentration of the salt or salts in the polymer solution when the concentration of the salt or salts in the polymer solution is from 55 to 60 per cent, the salt or salts present in the coagulating bath being mutually soluble in water with that or those in the polymer solution and being or including a salt which is capable, at higher concentrations, of dissolving the polymer. The filament or film is preferably stretched without rupture, and thereafter substantially all residual salt removed from the filament or film by washing with or soaking in water. The filament or film may be removed from the coagulating bath, stretched without rupture and, as soon as it is superficially coagulated sufficiently to be self-supporting, may be conducted through a bath containing the same salts in the same relative proportions as in the coagulating bath, the concentration of the salts in the second bath being 0.1 to 0.4 times the concentration of the salt or salts in the polymer solution. The filament or film is then again stretched short of the breaking point, and substantially all the residual salt is washed out. Prior to this washing step the filament or film may be conducted through a third bath having a salt or salts concentration from 1 to 10 per cent of the concentration of the salt or salts in the polymer solution, and may then be stretched a third time without rupture. After treatment as above the filament or film may be soaked in pure water to remove residual salt, stretched in wet steam, and dried. The nature and relative proportions of the salts used in the polymer solution and the coagulation and after-treatment baths are preferably all the same. In the example a 10.5 per cent solution of polyacrylonitrile in a brine consisting of 35 per cent zinc chloride, 26 per cent calcium chloride and 39 per cent water is spun into a bath consisting of 22 per cent zinc chloride, 16 per cent calcium chloride and 62 per cent water. After 10 seconds the filaments are withdrawn from the bath, stretched to 4.5 times their original length, conducted for 5 seconds through a second coagulating bath consisting of 12.6 per cent zinc chloride, 9.4 per cent calcium chloride and 78 per cent water, and stretched to 5 times their original length. The filaments are then soaked in water for 10 seconds to reduce their salt content further, and stretched in wet steam to 10 times their original length. Finally they are soaked for 10 seconds in water to remove remaining salt, and dried in an air oven.