GB618584A - Making solutions of cellulosic material - Google Patents

Abstract

Cellulosic material of mean fibre length of not more than 200 microns is mixed with a solution of an alkali-metal hydroxide of a concentration at least equal to the salting-out concentration for dissolved cellulose, and the mixture so made is then diluted with water to give a concentration of alkali-metal hydroxide not greater than 12 per cent, the cellulosic material being thereupon dissolved in the diluted alkali solution. Preferably the mixture is diluted with water at a temperature below 5 DEG C., but above the temperature at which any inorganic component of the solution begins to crystallize as by freezing of the water present. The cellulosic fibres may be preliminarily subjected to a treatment to reduce their viscosity characteristics, e.g. they may be heated in alkali-free condition. The material may be comminuted by cutting, grinding, or shredding. As cellulosic material there may be used cotton, cotton linters, wood pulp, scrap rayon, or a methyl, ethyl, or hydroxyethyl cellulose ether. Fineness of the particles may be determined microscopically or by observation of the proportion of water required to form a slurry. Material of the required fineness forms a slurry with as low a proportion of water as 7 parts water to 1 part of fibre. The comminuted cellulose may be suspended initially in part of the water required for making the solution. To the slurry there is then added dry or very concentrated caustic soda sufficient to form a caustic soda solution of about 15-50 parts of caustic soda for 100 parts of water, e.g. to form a 16-30 per cent caustic soda solution. Water is then added to bring the concentration down to about 8-12 parts of caustic soda per 100 parts of water. Dilution may be effected by adding ice. The cellulosic solution obtained may be stabilized by warming it promptly to 15 DEG -25 DEG C. In an example, wood-pulp is comminuted to the required fibre length and heated to reduce its viscosity. It is then soaked in 40 per cent caustic soda solution. The pressed material is shredded and kneaded and then water is added at 10 DEG -30 DEG C. A clear solution is obtained. In another example cellulose methyl, ethyl, or hydroxyethyl ether of fibre length less than 200 microns is treated with 42 per cent caustic soda solution and the mixture is diluted to form a solution. Sulphite wood pulp in the form of a slurry in water is ground in a ball mill until a sample of the ground pulp can be slurried with four parts of water to one of the pulp. The pulp is then heated with hydrogen peroxide. The reduced viscosity pulp is formed into a slurry and solid caustic soda is added. Cracked ice is added and the mixture is stirred until the cellulose has dissolved. Cut rayon or regenerated cellulose film waste may be used instead of wood pulp or cellulose ethers. The solutions may be used for making regenerated cellulose or cellulose ether sheets, threads, or coatings. Sulphuric acid or other acids or salts may be used for precipitating the cellulosic material from the solutions. Specification 587,153 is referred to. The Specification as open to inspection under Sect. 91 comprises also the production of solutions of cellulose or cellulose ethers in sodium zincate solutions. This subject-matter does not appear in the Specification as accepted.