GB696888A - Production of water-soluble cellulose ethers - Google Patents

Abstract

Water-soluble cellulose ethers are made by wetting a dry fibrous mass of a low-etherified water-insoluble, alkali-soluble cellulose ether with an aqueous solution of an alkali metal hydroxide insufficiently concentrated to dissolve the ether, slowly adding an alkylating, hydroxy-alkylating or carboxy-alkylating etherifying agent in small amounts over a period of hours while maintaining the temperature at 15-30 DEG C., allowing the mixture to stand at 15-30 DEG C. until the water-soluble ether is produced, and thereafter neutralizing the product. The starting material may be an alkyl, hydroxyalkyl (such as hydroxy-ethyl) or carboxy-alkyl cellulose ether (or a mixed cellulose ether), and is preferably soluble in aqueous solutions containing 3 per cent or more of alkali metal hydroxide. In such cases aqueous solutions containing from less than 3 per cent down to 0.3 per cent of alkali metal hydroxide are used for wetting the ether. The etherifying agent may be an alkyl ester of an inorganic acid, e.g. dimethyl or diethyl sulphate or methyl sodium sulphate, an alkyl halide such as methyl or ethyl p chloride or bromide, an alkylene oxide such as ethylene or propylene oxide, a glycide, a halohydrin such as ethylene, propylene, or glycerine chlorhydrin or epichlorhydrin, or a carboxyalkylating agent such as chloracetic or chloropropionic acid or sodium chloracetate. The neutralizing agent may be an alkali metal salt of a polycarboxylic acid having at least one free carboxyl group, such as sodium acid citrate or tartrate, an organic carboxy acid or an acid salt of an inorganic acid, e.g. an acid phosphate or a bisulphate. In an example, 100 parts of a dry fibrous hydroxyethyl cellulose ether having 0.2-0.4 ethylene oxide groups per anhydroglucose unit, 150 parts of a 0.3 per cent aqueous sodium hydroxide solution and 0.6 parts of a 40 per cent aqueous solution of sodium 2-ethyl hexanol sulphate (a wetting agent) are mixed at 18-20 DEG C., introduced into a churn and 50 parts of ethylene oxide admitted over a period of 3 hours at 15-18 DEG C. with mixing, the internal pressure of the churn being maintained at 28 inches of mercury. The reaction is allowed to continue at 15-18 DEG C. for 17 hours, with or without mixing, and 2.15 parts of sodium acid tartrate are then added.