Patent GB-770662-A (GB)
Title: Improvements in or relating to a method for insolubilising artificial filaments, threads, fibres and the like obtained by the spinning of solutions of proteins
Inventor: DAVIDSON WALTER LAMB
IPC: D01F4/00
Filed: 1954-04-23
Abstract: In processes wherein artificial protein filaments are hardened by treatment with an aqueous formaldehyde solution and then heated to dry and insolubilise them, the filaments are treated before the hardening step with a concentrated aqueous solution of at least one nonhardening salt at a pH up to 6, the solution being kept in contact with the filaments until a sample bundle of filaments, on washing and drying, gives discrete filaments.  Examples of non-hardening salts are the alkali-metal salts of hydrochloric, sulphuric or phosphoric acid, magnesium sulphate or ammonium sulphate, known hardening salts such as aluminium or chromium salts being excluded.  Preferably, after the filaments have been impregnated with the formaldehyde solution, they are stretched, e.g. 160 per cent, and held in the stretched condition while undergoing drying at least long enough to ensure that they no longer tend to shrink, before they are heated to such a temperature and for such a time as to effect insolubilization. The filaments may be dried at 15-160 DEG  C. and insolubilized at 120-180 DEG  C.  The aqueous solution of at least one nonhardening salt should preferably have a concentration of over 10 per cent. The period of time for which the filaments are retained in contact with the salt solution depends upon the temperature of the treatment and may be 18 hours at 25 DEG  C., 15 minutes at 50 DEG  C., 10 minutes at 70 DEG  C. and 5 minutes at 90 DEG  C.  The pH of the formaldehyde solution used to impregnate the filaments may be 0.5-11.0 and is preferably 0.5-2.5, 6.5-7.5, or 9.5-11 and the solution may contain 10-37 grams formaldehyde per 100 c.c..  The formaldehyde solution is preferably free from the non-hardening salts mentioned, but if its pH is to be 6.5-7.5, a small proportion of, for example, sodium borate, sodium aluminate, sodium tungstate, sodium stannate, ammonia, pyridine or caustic soda may be introduced.  The acid used to bring the pH of the solution to the acid side of neutrality is preferably hydrochloric acid.  If the pH of the solution is to be 9.5-11, a small proportion of sodium stannate, sodium aluminate or sodium hydroxide may be added.  The hardening agent is preferably an aqueous solution of formaldehyde which may be saturated with sodium chloride or with sodium sulphate and may have a pH of about 4.5.  At some stage prior to the heating step, the filaments may be treated with a compound giving rise to a cyanate ion, e.g. nitro-urea or potassium or sodium cyanate, suitably prior to or after treatment with a hardening agent or after they have been washed free from salt or after they have been treated with the formaldehyde solution used prior to the final drying and insolubilizing step.  Furthermore, the filaments may be subjected to the action of polymetaphosphate prior to treatment with the hardening agent, e.g. by including a polymetaphosphate in the alkaline protein spinning solution or by treating the filaments with an aqueous solution of a polymetaphosphate.  The polymetaphosphate may have 4-70 phosphate units in a chain or may have a molecular weight of the order of 2 million.  The treatment with the polymetaphosphate is preferably carried out at 50-90 DEG  C.  Insolubilization may be effected at 140-180 DEG  C., e.g. 160 DEG  C. for 10 minutes, and may be carried out in an inert atmosphere such as nitrogen.  In an example, a matured alkaline solution of peanut globulin is spun into an aqueous 2 per cent sulphuric acid and 24 per cent sodium sulphate solution at 30 DEG  C., the coagulated filaments are stretched 400 per cent in a bath of the same composition, and passed through an aqueous 22 per cent sodium sulphate and 2.5 per cent sodium chloride solution of pH 8-9 and at 25 DEG  C.  The filaments are then heated for 10 minutes at 70 DEG  C. in an aqueous bath of the same salt content at pH 4, hardened in a 20 per cent sodium sulphate, 2.5 per cent sodium chloride and 1.5 per cent formaldehyde solution of pH 5 for 7 minutes at 50 DEG  C., washed free from salt, mangled, impregnated with a 10 per cent formaldehyde solution brought to pH 1.5 with hydrochloric acid, and again mangled.  The filaments are thereafter dried and heated at 160 DEG  C. for 40 minutes to insolubilize them. Specifications 513,910, 533,952, 596,536, 597,497 [all in Group IV], 605,830, 623,460, 642,359, 654,513, 708,057, 742,001 and 758,560 are referred to.