GB866334A - Improvements in the production of alkali metal carboxymethyl cellulose - Google Patents

Abstract

An alkali metal salt of carboxymethyl cellulose is made by intimately mixing alkali cellulose and monochloracetic acid in an aqueous medium comprising a lower alkanol having 2-4 carbon atoms, extruding the resulting mass through a die so as to distribute the liquid component thoroughly and uniformly through the mass, breaking up the extruded column and allowing the resulting material to stand, with or without mild agitation, until the reaction has taken place. The terms "alkali" and "alkali metal" are used to refer only to sodium and potassium, and the alkanol is preferably ethanol, but may be isopropanol or tert. butanol. Preferably the aqueous medium comprises 0,4-1,2 parts of water, especially 0,60-0,83 parts, per part of cellulose, and 1,0-2,5 parts of the lower alkanol, especially 1,6-2,0 parts, per part of cellulose, and at least 75% of the water and at least 35% of the lower alkanol were present during the formation of the alkali cellulose (all parts are by weight). The ratio between the total free and combined caustic alkali and monochloracetic acid, should be between 0,88 : 1 and 1,10 : 1 where caustic soda is used, preferably from 0,95 : 1 to 1,0 : 1, and especially from 0,95 : 1 to 0,97 : 1. Desirably, the extruded material is mildly agitated for at least 2 hours at 50 DEG -70 DEG C. The alkali cellulose may be made by intimately mixing comminuted cellulose, in an aqueous medium at most 3,7 times the weight of the cellulose, with caustic alkali, preferably caustic soda, extruding the resulting mixture under pressure, and allowing the extruded material, preferably after it has been disintegrated, to stand, with or without mild agitation, until the alkali cellulose is produced. Preferably, the comminuted cellulose has no particles larger than 10 mesh and the process is carried out at below 50 DEG C. The aqueous medium may contain less than one part of water per part of cellulose, and may contain an alkanol having 2-4 carbon atoms, preferably ethanol. The extruded alkali cellulose may be allowed to stand at least 10 minutes, preferably at least 15 minutes in the case of soda cellulose, after disintegration. In each stage of the process, the reaction mass is desirably extruded through a die having a single opening of adjustable crosssectional area. U.S.A. Specifications 2,505,125 and 2,517,577 are referred to.