GB863425A - Oriented polyacrylonitrile film and process of manufacture - Google Patents

Abstract

863,425. Polyacrylonitrile films. DU PONT DE NEMOURS & CO., E. I. May 14, 1959 [June 2, 1958], No. 16633/59. Addition to 760,076. Drawings to Specification. Class 2(2). The process of the parent Specification (wherein an aqueous dispersion of a water-insoluble organic polymer, such as an acrylonitrile homopolymer or copolymer, in an aqueous solution of a metal salt, said salt being one which in concentrated aqueous solution dissolves the polymer and which is present in a proportion of at least 50% by weight of the polymer but in a proportion insufficient to form a salt solution which dissolves the polymer, is formed into the shape of a shaped article such as a film, water is evaporated from the shaped dispersion until the polymer particles coalesce, and salt is washed from the resultant shaped article) is modified in that a dispersion of an acrylonitrile homopolymer or copolymer containing a molar ratio of polymer to solvent salt of 0À5 to 6, and from 60 to 98 mole per cent of water, based on a total of 100 mole per cent of the polymer, salt and water, is formed into the shape of a film and, after water has been evaporated from the film until coalescence occurs, the film is stretched in a gaseous atmosphere to elongate at least one dimension of the film while maintaining the mole per cent of water between 30 and 80. Thereafter the salt is washed from the stretched film and the film is dried while maintaining it under tension effective to restrict its shrinkage during both washing and drying. In an example, an aqueous dispersion of polyacrylonitrile is prepared by agitating in a closed vessel in an atmosphere of nitrogen 0À10 part of potassium persulphate, 1À0 part of sodium lauryl sulphate, 120 parts of water and 80 parts of acrylonitrile. Into 160 parts of the dispersion at -4‹C. there is stirred 240 parts of 28% aqueous calcium thiocyanate solution at -7‹C., the mixture is cast at room temperature as a coating on a glass plate, the coating is partially dried and the resultant film is stripped from the plate in air at about 25‹C. and 50% R.H. The film is then biaxially stretched and, while in the stretched condition, washed with water at room temperature and dried. The dispersed polymer may be a copolymer of acrylonitrile with up to 25% of at least one other vinyl-type monomer such as styrene, acrylic and alkacrylic esters, methacrylonitrile, vinyl stearate, vinyl acetate, vinyl chloride, a vinylarylsulphonic acid or its salt, N-vinyl pyrrolidone, or 2-methyl-5-vinyl pyridine. Specifications 586,881, 597,368 and 765,585 also are referred to.