Improvements in or relating to a method for insolubilising artificial filaments, threads, fibres and the like obtained by the spinning of solutions of proteins

Insolubilized protein filaments, threads or like products are produced from a bundle of protein filaments which has been treated in succession with at least two hardening agents by impregnating the hardened filaments with an aqueous solution of formaldehyde of pH 0.5-1.5, drying the treated bundle below 100 DEG C. and then heating it at 140-180 DEG C. at least until the individual filaments are insolubilized. The hardened filaments are preferably stretched, e.g. 200 per cent, after their impregnation with the formaldehyde solution and dried in the stretched condition. The hardening treatment may comprise treating the coagulated and relaxed filaments with at least one solution of aluminium sulphate, polymeric sodium metaphosphate or sodium zirconyl sulphate, washing the filaments free from salts, and then treating them with a salt-free formaldehyde solution at a pH of about 3.5. The hardened filaments may then be further treated as described above, while still wet or after having been dried. They may be dyed, e.g. with an aqueous solution of a dyestuff at 40 DEG C., before being treated with the formaldehyde solution of pH 0.5 to 1.5. In an example filaments of coagulated peanut globulin produced in a described manner are treated for 5 minutes at 50 DEG C. with a 10 per cent aqueous solution of aluminium sulphate brought to pH 3.3 with sodium hydroxide or borate, washed free from salts, further hardened by treatment for 3 minutes at 50 DEG C. with 10 per cent formaldehyde solution at pH 3.5, and thereafter impregnated with a 10 per cent formaldehyde solution brought to pH 1 with hydrochloric acid. The impregnated filaments are then stretched 200 per cent in air, mangled and thereafter thoroughly dried at 80 DEG C. and heated for 30 minutes at 160 DEG C. Specifications 513,910, 533,952, 593,928, 596,536, 597,497, 605,830, 623,460, 642,359 and 654,513 are referred to.