Patent GB-1129831-A (GB)
Title: Fibrils of polyacrylonitrile
Inventor: FURNESS VERA ISABELLA
IPC: D01F6/18
Filed: 1965-02-11
Abstract: 1,129,831. Fibrillatable polyacrylonitrile films. COURTAULDS Ltd. 10 Feb., 1966 [11 Feb., 1965], No. 5921/65. Heading B5B. [Also in Division D2] A process for the manufacture of a filament or film of polyacrylonitrile which may be fibrillated, comprises extruding a solution of polyacrylonitrile at a viscosity of at most 300 poises into an aqueous coagulant at a temperature of at least 20‹ C. to form a freshly coagulated filament or film having a microporous structure and stretching the filament or film to a draw ratio of at least 4: 1 in such a way that the pores of the freshly coagulated filament or film are extended to become striations in the stretched filament or film. By the term polyacrylonitrile is meant homopolymers of acrylonitrile and copolymers containing at least 80% by weight of acrylonitrile units, obtained by copolymerization with such other monomers as styrene, methyl acrylate, itaconic acid, methallyl sulphonic acid and its salts, vinyl acetate and vinyl pyridine. Copolymers containing 90 to 95% by weight of acrylonitrile units are preferred. Suitably the filament or film is stretched to a draw ratio of 5: 1 to 7: 1. The filament or film may then be mechanically broken along the striations to form fibrils by known methods, e.g. rolling the film under pressure, bending under tension over a sharp edge, impacting the film and violently vibrating it. In examples: (1) a copolymer containing 90% of acrylonitrile units, 8% of methyl acrylate units and 2% of itaconic acid units is dissolved in a 50% aqueous solution of sodium thiocyanate, to give a 10% copolymer solution at a viscosity of 102 poises, which solution was extruded through a multi-hole spinning jet into an aqueous liquor containing 10% of sodium thiooyanate maintained at 20‹ C. to form a bundle of 100 filaments. The freshly extruded bundle is heated by contact with water containing sodium thiocyanate leached from the filaments maintained at 60‹ C., and stretched in steam to a draw ratio of 5: 1. The never dried bundle is then pulled on to and over the sharp edge of a bar and finally washed and dried. By this process the filaments of the bundle which have a denier of 4À5 are fibrillated, to form fibrils having an average denier of 0-5. In Example 2, a copolymer solution similar to that used in (1), but at a viscosity of 156 poises, is used and extrusion is effected as before using the same aqueous coagulating liquor but at 25‹ C. and the multi-filament bundle is immediately immersed in water containing sodium thiocyanate leached from the filaments and pre-heated to 50‹ C. and then stretched in steam to a draw ratio of 7: 1. The bundle is washed free of solvent and while still wet, subjected for 20 minutes to beating in a machine normally used to beat wood pulp for making paper. Fibrils so produced have an average denier of less than 0À25, compared to the denier of the filaments of the yarn of 5À5. In Example 3 a copolymer solution is extruded as in Example 1 through a slot into the same aqueous coagulating bath as in Example 1 to form a film which is led over a number of supporting rollers immersed in the liquor, over a length of 50 inches. The film is then immersed in a bath of water containing sodium thiocyanate leached from the film and maintained at 45‹ C. and there stretched to a draw ratio of 2À5: 1. The film is finally stretched in steam to a final draw ratio of 6À5: 1, washed free of solvent and dried. Fibrillation is effected by pulling the film on to and over a sharp edge under tension, the average denier of the fibrils being from 0À5 to 1. In general, the fibrils obtained from the never dried film or filament have the property of contracting up to about 25% during drying and hence may be used in the manufacture of paper. Specified polyacrylonitrile solvents include dimethyl formamide, dimethyl acetamide, butyrolactone, dimethyl sulphoxide and sulpholane, and concentrated aqueous solutions of certain inorganic salts, e.g. the thiocyanate salts of the alkali and alkaline earth metals, zinc chloride and mixtures of magnesium and calcium chlorides.