Patent GB-726686-A (GB)
Title: Process for producing shaped articles from acrylonitrile polymers
IPC: C08J3/09
Filed: 1953-01-26
Abstract: Artificial fibres, filaments, films, foils, tubes and like shaped articles are obtained by extruding a solution of an acrylonitrile polymer in a solvent containing N,N-dimethylacetamide into a liquid or gaseous coagulating medium; excess of coagulating medium is subjected to a recovery process in which acetic acid is formed by hydrolysis of some of the N,N-dimethylacetamide; a mixture of these compounds is separated from the excess coagulating medium; a quantity of N,N-dimethylacetamide which is free from acetic acid is added to the mixture to maintain the concentration of acetic acid within the range of 1-4 per cent by weight, and the mixture is then re-used to make additional polymer solution for extrusion.  All the steps of the process may take place continuously and simultaneously.  The coagulating bath may be an aqueous solution of N,N-dimethylacetamide of 20-80 per cent concentration.  The overflow from the coagulating bath or, if a dry spinning process is used, the aqueous solution obtained by scrubbing or condensing the effluent vapours, and the overflow from subsequent washing baths, are passed through the recovery system.  Water is distilled off, and the residual liquor, which comprises N,N-dimethyl acetamide and acetic acid, is returned for re-use as a solvent for the acrylonitrile polymer.  Before this liquor is returned to the dissolving-vessel it is mixed with a proportion of N,N-dimethyacetamide, free from acetic acid, to replace solvent losses during the operation and to maintain the concentration of acetic acid within the range of 1-4 per cent.  Preferably the polymer is polyacrylonitrile itself or a copolymer containing at least 80 per cent of acrylonitrile in the polymer molecule.  A blend of such a polymer with another polymeric substance may be used. Copolymers of acrylonitrile with other acrylic or methacrylic acid derivatives or with vinyl or vinylidene chloride, vinyl acetate, styrene, alkyl fumarates or maleates, vinyl phthalimide, vinyl succinimide, 2-vinylpyridine, 2 - methyl - 5 - vinyl - pyridine or N-vinylimidazole may be used.  In an example, a solution of a copolymer of acrylonitrile and vinyl acetate in N,N-dimethylacetamide containing 2 per cent of acetic acid is fed from a mixing tank to a storage tank, whence it is removed by a constant volume pump and extruded through a spinneret to form filaments.  The filaments are coagulated in a bath containing an aqueous solution of N,N-dimethylacetamide.  The bath may also contain isopropanol, glycerol, ethylene glycol, zinc chloride, lithium chloride, nitromethane or other additions. The filaments leave the coagulating bath and pass through a washing chamber where they meet a stream of warm or hot water. They pass over a drying drum and may then be stretched in presence of steam.  They may subsequently be crimped and cut into staple fibres.  Wash liquor, containing solvent removed from the filaments, is concentrated by evaporation of the water in a still until it contains 30-50 per cent of solvent.  The condensed water is returned to the washing chamber.  The concentrated solution of solvent is mixed with the overflow liquid from the coagulating bath and the mixture is passed into another still which is so operated that the bottom liquor leaving the still is substantially anhydrous. The condensed water is returned to the washing chamber.  The still bottom liquor consisting of a mixture of N,N-dimethylacetamide and acetic acid is passed to the polymer-dissolving tank.  To compensate for loss of solvent in the system and to maintain the concentration of acetic acid in the spinning solution at a constant value, additional acetic acid-free N,N-dimethylacetamide is added to the contents of the polymer-dissolving tank.  Specifications 663,500, 673,841 and 726,685 are referred to.