GB1191538A - Process for the preparation of Acrylic Fibres with Non-Circular Cross-Sections - Google Patents

Abstract

1,191,538. Polyacrylonitrile filaments of non- circular cross-section. TOYO RAYON K.K. 26 July, 1968 [31 July, 1967; 22 Sept., 1967; 8 Dec., 1967], No. 35896/68. Heading B5B. A process for the preparation of acrylic fibers with non-circular cross-sections comprises spinning an organic solvent solution of a polymer containing at least 85 mol per cent of acrylonitrile, at an extrusion rate of no higher than 10 metres per minute, through non-circular orifices of the desired configuration having a shape factor of not less than 16, the shape factor being defined as into a spinning bath which consists of an aqueous solution of an organic solvent at a concentration of 30-60% by weight and is maintained at a temperature not higher than 35‹ C., with a jet stretch of not less than 0À9. The upper limit of the shape factor is not critical, but the preferred value is 30 or less, especially 25 or less. The shape factor ranges such as to include equilateral triangles, regular squares, and certain rectangles, and the term fibres of non-circular cross-section is intended to cover fibres having normally polygonal crosssections. Preferably, the maximum jet stretch is of the order of 1À5, the optimum range being 1À0 to 1À2. The spinneret employed is preferably provided with orifices of which the perpendicular portion is at least 0À08 mm. in length. Fig. 4 shows a suitable spinneret orifice. The organic solvent in the spinning solution and the spining bath may consist substantially of dimethyl - sulphoxide, but other specified organic solvents include dimethylacetamide and dimethylformamide. In a preferred embodiment, the spinning solution is obtained by polymerization of acrylonitrile alone or of at least 85 mol per cent of acrylonitile and at least one other copolymerizable monomer, in an organic solvent consisting substantially of dimethylsulphoxide, in the presence of azobis-dimethyl-valeronitrile catalyst. Suitable copolymerizable monomers are listed. Alternatively, the spinning solution may be a liquid mixture of a dimethylsulphoxide solution of (A) a polymer containing at least 85 mol per cent of acrylonitrile and having an intrinsic viscosity ranging from 1À0-1À4, with another dimethylsulphoxide solution of (B) a polymer containing at least 85 mol per cent of acrylonitrile and having an intrinsic viscosity ranging from 1À6-2À0, the mixing ratio of the polymers (A) to (B) in the liquid mixture being 95 : 5 to 70 : 30, in terms of per cent by weight. By the method of the invention, fibers of polygonal cross-section in which no side is concave or depressed, i.e. a cross-section of a convex-side polygon, can be easily obtained. Orifices of triangular cross-section are advantageously used. Examples 1 to 3 and 5 to 10 relate to the production of triangular filaments, and example 4 to the production of rectangular filaments. In Examples 6 to 10, the as-spun filaments are drawn to 6 times in glycerine at 120‹ C., washed with water, and dried at 120‹ to 150‹ C., and may be relaxed to induce crimp.