GB570159A - Improvements in and relating to the production of crimped artificial threads by the viscose process - Google Patents

Abstract

Crimped continuous or discontinuous threads of high tenacity are obtained by extruding viscose into a spinning bath containing dilute sulphuric acid and sufficient metallic sulphates to delay the decomposition of the viscose into cellulose hydrate, withdrawing the filaments so produced from the spinning bath while they still contain at least 7 per cent of xanthate sulphur calculated on the dry weight of the cellulose, stretching the filaments in the presence of hot dilute acid at a temperature of at least 60 DEG C., maintaining the stretched filaments under tension in the same or a further acid bath at a temperature of at least 60 DEG C. until the decomposition of the cellulose xanthate is completed and the filaments are substantially free from xanthate sulphur, and subsequently relaxing the filaments in the presence of water, preferably hot water. The concentration of sulphuric acid which may be used for the hot acid conversion bath may be 0.15-1.5 per cent and the temperature may be 80-95 DEG C. In the production of staple fibre, a number of stretched threads may be collected and formed into a thick tow and led directly through an aqueous acid bath and thence to a cutting-machine. The aqueous bath in which the filaments are relaxed may contain caustic soda or ethylene diamine to enhance the crimp. If desired, the thread after being washed free from acid while under tension may be dried and wound on bobbins without relaxation. The crimp is developed on subsequently relaxing the thread in water. The percentage xanthate sulphur in the filaments as they leave the spinning bath is determined by running a length of thread corresponding to about 5 grams in weight of dry cellulose into a saturated aqueous solution of ammonium chloride and sodium bicarbonate, allowed to stand till all the acid is neutralized and then washed with a further amount of the solution. The thread is transferred to a bottle containing distilled water, potassium iodide, acetic acid, and a measured volume of a standard iodine solution. After 2-3 hours, the unchanged iodine is back titrated with sodium thiosulphate solution. The thread is removed, dried, and weighed, and the percentage of sulphur on the weight of dry cellulose is calculated. The percentage of xanthate sulphur in the threads emerging from the spinning bath is dependent upon the time of treatment, the acid content of the bath, the total denier of the thread, and the alkali content of the viscose. In an example, viscose containing about 7 per cent of cellulose and 9 per cent of caustic soda is extruded into a solution containing sulphuric acid, zinc sulphate, and sodium sulphate at 50 DEG C., the coagulated filaments remaining in the bath for a distance of 20 centimetres. The thread then passes through a bath containing dilute sulphuric acid, sodium sulphate, and zinc sulphate at 95 DEG C., and is stretched between two rollers. The stretched thread is passed through hot dilute sulphuric acid to complete the conversion to cellulose hydrate and is then passed through hot water. The washed thread is passed to a cutting-machine and the fibres become crimped immediately on cutting. Specifications 289,028, [Class 31 (i)], and 467,500 are referred to.