Improvements in or relating to a method for the production of artificial filaments, threads, fibres and the like

A bundle of artificial filaments or like products, obtained by the spinning of solutions of protein in aqueous media into acidified saline coagulating baths, is treated with a concentrated aqueous solution of at least one nonhardening salt at a pH up to 7 at least until a sample of the bundle, on washing and drying, gives discrete filaments; the bundle is then washed until free from salt and heated to such a temperature and for such a time that the filaments are dried and retain their fibrous form on drying after immersion for 90 minutes in an aqueous solution containing 0.1 per cent of sulphuric acid and 0.25 per cent of sodium sulphate at 97 DEG C. The resulting bundle may be wetted with water, stretched, e.g. 200 per cent in air, dried in the stretched condition until the filaments no longer tend to shrink, and then heated, e.g. at 160 DEG C., until their strength is improved. Non-hardening salts which may be used include the alkali-metal salts of hydrochloric, sulphuric and phosphoric acids and sulphates of magnesium and ammonium. Among the salts which are excluded are the known hardening salts, e.g. aluminium, chromium, zirconium and titanium salts. The temperature of the salt solution may be 25-90 DEG C. and the contact time may be 18 hours at 25 DEG C., 30 minutes at 50 DEG C., 20 minutes at 70 DEG C., or 10 minutes at 90 DEG C. The filaments may be pretreated by immersion in a cold solution of a non-hardening salt, e.g. sodium sulphate, at pH 8 to 9. The heating of the bundle may be carried out in two stages, e.g. the filaments may first be dried by heating at temperatures up to 100 DEG C. and the dried filaments then heated at 140-220 DEG C., and particularly at 160 DEG C., for 2 hours. In an example a bundle of coagulated protein filaments, formed by spinning a matured alkaline aqueous solution of peanut globulin into an acidified saline coagulating bath and stretched 400 per cent in a bath of the same composition, is passed through an aqueous bath containing 22 per cent of sodium sulphate and 2.5 per cent of sodium chloride at a pH of 8 to 9 at 25 DEG C. so that the liquor adhering to the bundle emerging from the bath has a pH of 3 to 6. The filaments are then heated in an aqueous bath of 22 per cent sodium sulphate at pH 4 for 10 minutes at 70 DEG C., washed free from salts, dried at 40 DEG C, and heated at 160 DEG C, for 2 hours.