GB351401A - Process for the manufacture of viscose solutions - Google Patents

Abstract

Viscose is prepared from a lowpolymerized cellulose, substantially free from hemicellulose, by a process in which expression, disintegration and ripening of the alkali cellulose are omitted, the cellulose being treated with all or a part of the necessary caustic soda at mercerizing concentration, and the mixture being treated with carbon bisulphide and then with water or, if all the caustic soda was not added at the first stage, with caustic soda solution. The cellulose employed has a copper viscosity, determined as described below, of less than 10, <PICT:0351401/IV/1> preferably than 5, and may be obtained by particularly energetic boiling in the manufacture of sulphite pulp, or by particularly powerful bleaching of sulphite pulp or cotton, or from various kinds of grass and straw; cellulose hydrate is suitable also. In p any event, the cellulose must be freed substantially from hemicellulose, e.g. by alkaline treatment. The cellulose may be used in sheet or flocculent form, and is preferably taken in a moist or wet state and preliminarily ground. The conversion to soda cellulose may be effected at ordinary or reduced temperature, the minimum concentration of the caustic soda being about 9 per cent at just above 0 DEG C., about 11 per cent at 15 DEG C. and 12-13 per cent at 20 DEG C. The treatment with carbon bisulphide may be effected while stirring or kneading, at least intermittently; 60-80 per cent of carbon bisulphide, calculated on the air-dry pulp, may be used at a temperature of 10-15 DEG C. Excess of carbon bisulphide may be removed by evacuation. In an example, freshly boiled pulp that has been bleached and freed from hemicellulose, is wet-ground and stirred for 30 minutes in the form of a 25 per cent paste with 87,5 per cent by weight, calculated on the paste, of a 33 per cent solution of caustic soda at 10 DEG C. The product is stirred for 4 hours at 10 DEG C. with 20 per cent by weight, calculated on the paste, of carbon bisulphide, and the xanthate is then dissolved in water, filtered and evacuated. The Specification as open to inspection under Sect. 91 (3) (a) is not restricted to the use of cellulose that has been freed substantially from hemicellulose. Also, it includes an example in which viscose is prepared from air-dry pulp substantially as in the example given above. This subject-matter does not appear in the Specification as accepted. Viscosimeters.-To determine the copper viscosity of the cellulose used, an ammoniacal-copper solution of a given weight of the cellulose is prepared under conditions indicated in the Specification. The solution is placed in a bottle, as shown, into which air is forced through the tube b so as to force the solution to the upper mark on the tube a. The capillary tube c is then adjusted so that its lower end just touches the surface of the liquid in the bottle, and the time taken by the solution to flow from the upper to the lower mark on the tube a is observed. This time, divided by the water value of the viscosimeter, is the copper viscosity of the cellulose.