GB659506A - Improved method of making methyl carboxyalkyl ethers of cellulose - Google Patents

Abstract

Cellulose fibres are immersed in a 5 to 27.5 per cent aqueous solution of a carboxy alkylating agent, pressed to bring the amount of retained carboxy-alkylating agent within 0.05 to 0.22 parts by weight per weight of cellulose, immersed in a 40 to 55 per cent aqueous sodium hydroxide at a temperature not exceeding 60 DEG C., pressed to bring the alkali-cellulose ratio within 0.7 to 1.3, then methylated with 1.2 to 1.4 parts by weight of methyl chloride per part of cellulose under pressure below 80 DEG C., the methylation being stopped before the methylation exceeds 2.1 methoxyl groups per anhydro-glycose unit, the so-formed mixed ether being recovered by treatment with acidified water. Ethers containing 0.02 to 0.3 carboxyalkyl groups and 0.7 to 2.1 methyl groups per anhydro-glucose unit are so obtained. The products behave like carboxymethyl cellulose in media having a pH above 6 (i.e. they remain in solution at temperatures up to 90 DEG C. or higher), and like methyl cellulose when in acid aqueous media of pH 4-2 (i.e. gell at temperatures above about 55 DEG C.). Specified carboxyalkylating agents are choroacetic, chloropropionic and chlorobutyric acids and their salts. In an example a sheet of cotton linters is saturated with a 25 per cent aqueous solution of sodium chloroacetate at room temperature, and pressed to remove excess. It is then dipped into 50 per cent aqueous sodium hydroxide at 25 DEG C. and again pressed. After shredding the treated sheet into a pressure vessel, 1-33 times its own weight of methyl chloride is added and the methylation carried out for 10 hours at 60-80 DEG C. Excess methyl chloride is driven off, 300 g. of the reaction mixture are stirred into 1700 c.c. of water containing 50 c.c. of concentrated hydrochloric acid at 90 DEG C. Filtration is carried out in a basket centrifuge and the solids washed with hot distilled water at 75 DEG C. After drying, the acid product is spread in a thin layer on a steel pan and sprayed with just enough 25 per cent caustic soda to neutralize the carboxyl groups present. The product contained 1.45 methoxyl groups and 0.14 carboxymethyl groups per anhydroglucose unit. Example 3 describes the production of an ether containing 1.83 methoxyl and 0.10 carboxyethyl groups per anhydroglucose unit.