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

A process for insolubilizing bundles of coagulated protein filaments comprises subjecting the filaments to the action of a soluble alkali metal polymetaphosphate before subjecting them to a formaldehyde harding treatment, and thereafter impregnating the hardened filaments with an acidified solution of formaldehyde; the bundle is then stretched and, while stretched, is heat-dried until there is no further tendency to shrink, whereupon the bundle is further heated to such a temperature and for such a time as to effect insolubilization. The polymetaphosphate, which may, if desired, be incorporated in the spinning solution, has 4-70 or more phosphate units in the chain (up to molecular weights of the order of 2 million), and the treatment with this solution is best carried out at 50-90 DEG C. If desired, the hardening treatment may be carried out in two stages, in which case the first hardening solution, which may be of aluminium sulphate or sodium zirconyl sulphate, is used before the polymetaphosphate treatment, which is then followed, as before, by the formaldehyde hardening treatment. The acid formaldehyde solution is preferably salt-free and at pH 1-4. The degree of stretch imparted to the filaments may be of 50-500 per cent, preferably 100-400 per cent, and the drying of the filaments is carried out at 0-160 DEG C.; the subsequent insolubilization is accomplished at 120-180 DEG C., preferably 140-180 DEG C. If desired, pigments may be incorporated in the spinning solution from which the filaments are obtained. Specifications 513,910, 533,952, 597,497, [all in Group IV], 605,830, 623,460 and 642,359 are referred to.