Patent GB-726685-A (GB)
Title: Process for producing shaped articles from acrylonitrile polymers
IPC: C08J3/09
Filed: 1953-01-26
Abstract: Artificial fibres, filaments, yarns, films, foils, tubes and like articles are obtained by extruding a solution of an acrylonitrile polymer in a solvent comprising N,N-dimethylacetamide and 1-4 per cent by weight of acetic acid into a liquid or gaseous coagulating medium, and excess of coagulating medium is subjected to a recovery process in which acetic acid is formed by hydrolysis of part of the N,N-dimethylacetamide; the mixture of these compounds is separated from the excess of coagulating medium; some of the acetic acid is removed from the mixture so as to maintain the concentration of acetic acid in the system constant, and the mixture is then used for dissolving acrylonitrile polymer so as to form additional solution for extrusion.  The coagulating bath may be an aqueous solution of N,N-dimethylacetamide.  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 comprising N,N-dimethylacetamide and acetic acid is returned for re-use as a solvent for the acrylonitrile polymer.  A portion of this liquid is treated for removal of the acetic acid and then returned to the main stream of recovered solvent.  Preferably, the polymer used is polyacrylonitrile itself or a copolymer containing at least 80 per cent by weight of acrylonitrile in the polymer molecule.  A blend of such a polymer or copolymer with another polymeric substance may be used.  A copolymer of acrylonitrile with vinyl acetate, styrene, chloracrylic acid, methacrylic acid, acrylamide, vinyl chloride, vinylidene chloride, an alkyl acrylate, an alkyl fumarate, N-vinyl phthalimide, a vinyl pyridine or N-vinyl imidazole may be used.  The polymer may be a ternary polymer comprising acrylonitrile, methacrylonitrile or vinyl acetate, and a vinyl pyridine, vinyl chloride or 1-vinyl imidazole.  In an example, a copolymer containing 95-97 per cent of acrylonitrile and 3-5 per cent of vinyl acetate is dissolved in a mixture of N,N-dimethylacetamide and acetic acid, and the solution is conveyed to a storage tank whence it is removed by a constant volume pump and delivered to a spinneret.  The solution is extruded into an aqueous coagulating bath containing 20 to 80 per cent of N,N-dimethylacetamide.  The coagulating bath may contain additions such as isopropanol, glycerol, ethylene glycol, zinc chloride, lithium chloride or nitromethane.  The coagulated filaments pass from the bath to a washing chamber or bath where they meet a stream of warm or hot water, and they may then pass over a drying drum and through a stretching device to a collecting bobbin.  A portion of the used wash liquor is passed into the spinning bath but the remainder is passed to a still where it is concentrated till it contains 30-50 per cent of solvent.  The condensed water is returned to the washing chamber.  The concentrated wash liquor is mixed with the overflow from the coagulating bath and the mixture is passed to another still which is operated at such a pressure and temperature that the bottom liquor is substantially anhydrous and consists of recovered solvent and acetic acid formed in the stills by hydrolysis of the N,N-dimethylacetamide.  A portion of this liquor is passed to a tank in which it is treated with alkali such as sodium hydroxide, and the neutralized liquor is then flash-distilled in another still. From this still, N,N-dimethylacetamide, free from acetic acid, flows to join the main stream of recovered solvent, which is led to the polymer dissolving tank.  The relative proportions of recovered solvent which passes directly to the dissolving tank and of that which is first treated for removal of acetic acid may be varied by means of valves.  If desired, the neutralization step may be omitted, the separation of acetic acid from the N,N-dimethyl acetamide being effected by fractional distillation. Specifications 663,500, 673,841 and 726,686 are referred to.