GB645390A - Improvements in and relating to the production of artificial protein threads, filaments and the like - Google Patents

Abstract

Freshly spun artificial protein threads are hardened in a bath containing formaldehyde and one or more metal salts other than sodium chloride and then treated at a temperature of from 35 DEG to 60 DEG C. in an insolubilizing bath containing from 500 to 800 grams of sodium bisulphate and from 5 to 15 grams of formaldehyde per litre. Suitable metal salts are sodium sulphate, magnesium sulphate, and aluminium salts such as aluminium sulphate. Threads so treated have improved resistance to attack by boiling water and hot dilute acids. The insolubilizing bath may also contain free sulphuric acid up to 200 grams per litre, and the time of insolubilizing treatment is usually from 1 to 4 hours. The hardening step (which may be effected in one or two stages with stretching in between them) is carried out at 40 DEG to 70 DEG C. in a solution of pH 3.0 to 8.0 and containing 5 to 15 grams formaldehyde per litre. The time of treatment is from 1 to 4 hours. Both the hardening and insolubilizing treatments may be carried out on thread-advancing reels in the baths or on a continuous thread in a series of convolutions. In an example a 17 per cent solution of milk casein in an aqueous 1.2 per cent caustic soda solution is extruded into a coagulant bath containing 360 grams sodium sulphate and 40 grams sulphuric acid per litre. It is then stretched and hardened simultaneously, the hardening taking place in two stages, the first in a bath containing per litre 300 grams sodium sulphate, 10 grams formaldehyde and 5 grams sulphuric acid for 15 minutes at 45 DEG C., the second in a bath containing per litre 250 grams sodium sulphate and 10 grams formaldehyde for 10 minutes at 55 DEG C. It is then fed continuously through an impregnating bath at 50 DEG C. containing per litre 400 grams of sodium sulphate and 10 grams formaldehyde, and then fed in convolutions into a hardening bath of the same constitution and at the same temperature, and hardened for two hours. Excess hardening solution is removed by squeeze rollers and the thread fed in convolutions into an insolubilizing bath at 40 DEG C. containing per litre 400 grams sodium sulphate, 352 grams sulphuric acid (equivalent to 676 grams sodium bisulphate and 76 grams sulphuric acid) and 10 grams formaldehyde. After 2 hours treatment in this bath the thread is washed with water and 0.5 per cent aqueous sodium bicarbonate and dried. Specifications 502,710, 565,011 and 597,497 are referred to. The Provisional Specification also refers to Specification 618,925.