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

A continuous travelling tow of protein filaments, obtained by spinning aqueous alkaline solutions of vegetable seed globulins or of phosphoto-proteins into an aqueous sulphuric acid/sodium sulphate bath, is insolubilized in 1-30 minutes under conditions substantially free from tension by impregnating the tow with a concentrated aqueous solution at a pH up to 7 of at least one salt from the group consisting of the alkali metal salts of sulphuric acid, ammonium sulphate and magnesium sulphate, which solution is substantially free from sodium chloride, retaining the solution in contact with the tow at 40-98 DEG C. at least until a sample thereof on washing and drying gives discrete filaments, impregnating the thus treated tow at a temperature up to 80 DEG C. with an aqueous formaldehyde solution of pH 4-7 which contains at least 210 g. of sodium sulphate per litre of solution and is substantially free from sodium chloride, and thereafter impregnating the tow at a raised temperature, e.g. 70-98 DEG C., preferably 90-98 DEG C., with an aqueous formaldehyde solution substantially free from sodium chloride and containing, per litre of solution, at least 340 g. of sodium sulphate and at least 200 g. of sulphuric acid. Preferably, prior to impregnating the tow with the concentrated aqueous solution of pH up to 7, the tow is treated in a relaxing solution containing not less than 220 g. of sodium sulphate per litre of solution. The concentration of the aqueous solution of pH up to 7 should preferably exceed 10 per cent, and the tow is retained in contact with this solution for a time depending upon the temperature, e.g. 15 minutes at 50 DEG C., 10 minutes at 70 DEG C. or 5 minutes at 90 DEG C. In an example, a tow of protein filaments spun from a solution of groundnut globulin is passed, while being stretched, through an aqueous solution containing 240 g/l. of sodium sulphate and 20 g/l. of sulphuric acid and is then passed through an aqueous solution containing 240 g/l. of sodium sulphate at pH 8-9 at 25 DEG C., so that the filaments emerge with liquor adhering to them with a pH 3-6. Thereafter the tow is heated in a bath of the same salt content at pH 4 for 10 minutes at 70 DEG C. in a ring trough, according to the method of Specification 623,460, passed between squeeze rolls, and treated for 5 minutes at 50 DEG C. with an aqueous solution of 240 g/l. of sodium sulphate and 15 g/l. of formaldehyde in a second ring trough. Finally the tow is mangled between a secon