GB469391A - Improvements in or relating to the manufacture of cellulose ethers - Google Patents

Abstract

Water-soluble methyl ethers of cellulose are obtained by a two stage process comprising the treatment of cellulosic material in the presence of aqueous alkali with a restricted proportion of dimethyl sulphate in such manner as to form a simple methyl ether insoluble in water but capable of being brought into solution in dilute caustic soda, and the subsequent treatment of the intermediate product with a lower alkyl chloride at a raised temperature. If desired, a further proportion of aqueous alkali may be added to assist the second etherification step. If a simple methyl ether of cellulose is required, methyl chloride is used for the second etherification step. Mixed cellulose ethers are obtained if other alkyl chlorides such as ethyl chloride are used. The etherification with dimethyl sulphate may be carried out in an incorporating machine of the kind used for kneading soda cellulose. It may be carried out at raised temperature and in the presence of not more than 3 parts by weight of caustic soda for every 4 parts of dimethyl sulphate, and the latter may be mixed with a volatile diluent such as benzene. Dispersing agents may be added to assist penetration of the cellulose by the reagents. The methyl cellulose obtained in the first step of the process may contain 4--10 per cent of methoxyl per glucose unit of the cellulose. The second stage of the process is carried out in a pressure vessel such as an autoclave with stirring devices. Aqueous solutions of the cellulose methyl ethers may be used as adhesives, or sizes for paper, cloth, or leather. They may be used as thickening or emulsifying agents in aqueous coating compositions such as distempers. In examples, wood cellulose pulp is mixed with caustic soda solution and shredded. Dimethyl sulphate is added gradually and incorporation continued for some time, the temperature being maintained at 60 DEG C. or at room temperature. A further amount of caustic soda may then be incorporated. The mass is then placed in an autoclave and methylated at 80--100 DEG C. with methyl chloride. The product is purified by steaming and washing with hot water. In another example, wood cellulose pulp is mixed with caustic soda solution and shredded. A solution of dimethyl sulphate in benzene containing a dispersing agent known under the Registered Trade Mark "Perminal W" is added gradually. The mass is transferred to an autoclave and treated with ethyl chloride at 110--120 DEG C.