GB366987A - Improvements in the manufacture of solutions of fibroin - Google Patents

Abstract

Fibroin is dissolved in cuprammonia solution containing not more than 4 molecules of ammonia to one atom of copper, and preferably the solution is cooled during its preparation where practicable and during its storage, if any, to a temperature below 0 DEG C. and preferably 0 DEG to -15 DEG C. A solution is thus obtained of high viscosity suitable for the production of artificial silk. To reduce the degradation of the fibroin it is preferable to remove a part of the ammonia so that the solution contains not more than 2 molecules of ammonia to one atom of copper. This may be effected by suction or by passing through the solution a current of an inert gas, in which operation it may be necessary to raise the temperature to 25 DEG C.; or the fibroin complex may be precipitated from the solution by salt solutions such as ammonium sulphate, sodium sulphate or sodium chloride or by organic liquids soluble in water such as methyl or ethyl alcohol or acetone, the precipitate being then redissolved in water. The quantity of copper hydroxide should be not more than 30 parts copper to 100 p parts air-dry degummed fibroin. This avoidance of an excess of copper allows the solution to be filtered through a cellulose filter such as wadding without causing the filter mass to swell. If copper salts are used for the production of the solutions, there must be used sufficient alkali to convert all the copper into hydroxide, but excess of alkali should be avoided. In examples, (1) a paste of copper hydroxide containing 330 parts copper is kneaded at -2 DEG C. with 1000 parts degummed silk waste and 981 parts of 22 per cent ammonia; 2360 parts water are added and the solution after filtration is ready for spinning; (2) a paste of copper hydroxide containing 45 kilos copper is mixed with 165 litres of 22 per cent ammonia and 150 kilos of air-dry fibroin at -3 to -4 DEG C.; 150 litres of water are added during the introduction of the last half of the fibroin, and the mixture is stirred while slowly adding a further 350 litres of water and filtered; the solution is placed in a closed vessel having a stirrer or in a rotary drum, and the pressure is reduced to 12-15 mm., the temperature being raised by a water jacket, but not above 25 DEG C.; if the solution contains less than 2 molecular proportions of ammonia, it is again filtered before being spun. Specification 366,963 is referred to.