GB785881A - Improvements in or relating to a new or improved method for insolubilising artificial filaments, threads, fibres and the like obtained by the spinning of solutions of proteins - Google Patents

Abstract

Artificial protein filaments are insolubilized by treating a bundle of the filaments with an aqueous solution of at least one hardening agent, washing the bundle with water until free from any residual salt derived from the hardening solution, stretching the filaments, impregnating them while stretched with an aqueous formaldehyde solution, drying them while stretched by heating up to 160 DEG C. at least until they no longer tend to shrink and then further heating them to 120-200 DEG C. until they are insolubilized, i.e. do not dissolve in 90 minutes at 97 DEG C. in 0.1 per cent aqueous sulphuric acid containing 0.25 per cent of sodium sulphate. The filaments, after stretching, for instance, up to 200 per cent, may be either wet or dried prior to the impregnation with formaldehyde solution. Prior to the treatment with the hardening agent the filaments may be treated with a concentrated aqueous solution of at least one non-hardening salt at a pH up to 6, e.g. a solution containing over 10 per cent of an alkali metal salt of hydrochloric, sulphuric or phosphoric acid, magnesium sulphate or ammonium sulphate, the treating conditions being, for example, 18 hours at 25 DEG C., 15 minutes at 50 DEG C., 10 minutes at 70 DEG C. or 5 minutes at 90 DEG C. The pH of the formaldehyde solution used to impregnate the stretched filaments may be 0.5-2.5, 6.5-7.5, or 9.5-11, and its concentration may be 10-37 grams of formaldehyde per 100 c.c. of solution. The solution is preferably free from non-hardening salts but, if its pH is to be adjusted to 6.5-7.5, may contain a small proportion of sodium borate, aluminate, tungstate, or stannate or of ammonia, pyridine or caustic soda. Adjustment of the pH of the solution to 0.5-2.5 may be made with hydrochloric acid. The hardening agent is preferably formaldehyde, which may be dissolved in a saturated aqueous solution of sodium chloride or sulphate of pH about 4.5. The duration of the hardening treatment may be about 3 minutes. At any stage of the process up to the insolubilization step, e.g. prior to or after the hardening step or after washing free from salt, the filaments may be treated with an aqueous solution of sodium or potassium cyanate or nitrourea or other agent-yielding cyanate ions in aqueous solution. Furthermore, the filaments may be treated, prior to the hardening step, with a polymetaphosphate containing 4-70 phosphate units in a chain or having a molecular weight of the order of two million. The phosphate may be added to the alkaline protein spinning solution or the filaments may be treated with an aqueous bath of the phosphate at 50-90 DEG C. before the hardening step. The insolubilization may be effected at 140-180 DEG C., preferably at 160 DEG C. for 10 minutes. In an example, filaments produced by spinning an alkaline solution of peanut globulin into an acid-salt congulating bath and stretching them 400 per cent in a bath of the same composition, are relaxed for 5 minutes at 25 DEG C. in a bath containing 22 per cent of sodium sulphate and 2.5 per cent of sodium chloride at a pH of 8-9. The filaments are then hardened in a bath containing 20 per cent of sodium sulphate, 2.5 per cent of sodium chloride and 1.5 per cent of formaldehyde at a pH of 5-7 for 7 minutes at 50 DEG C., washed with water and dried at 80 DEG C. The dry hardened filaments are soaked with water, stretched 200 per cent in air, impregnated in the stretched condition with a formaldehyde solution brought to pH 1.5 with hydrochloric acid, dried in the stretched condition at 80 DEG C. until they no longer shrink when tension is removed, and finally heated for 30 minutes at 160 DEG C. in the relaxed condition. On washing the filaments with water a crimped wool-like appearance is imparted to them without loss of strength. Specifications 513,910, 533,952, 597,497, [all in Group IV], 605,830, 623,460, 642,359, 741,497, 742,261, 742,890, 758,560 and 770,662 are referred to.