GB611353A - Improvements in the production of cellulose derivatives - Google Patents

Abstract

Water-soluble organic esters of cellulose are obtained from solution in a mixture of water and a water-soluble organic solvent for the ester as solids or in concentrated aqueous solution substantially free from organic liquids by a process comprising subjecting the solution to extraction with a substantially water-insoluble liquid which is a solvent for the said water-soluble organic solvent and a non-solvent for the cellulose ester, thus substantially completely removing said water-soluble organic solvent from the solution of the cellulose ester, and then precipitating the cellulose ester from said solution or concentrating the solution without causing the cellulose ester to precipitate. The extraction of the water-soluble organic solvent may be carried out by addition of ethyl acetate, butyl acetate, petroleum ether and mixtures thereof, but isopropyl ether or a mixture of 70 per cent ethyl acetate and 30 per cent benzene by weight is preferred. The extraction may be effected at 10 DEG -70 DEG C. and preferably at about 40 DEG C., and it is continued until the solution contains between 0.01 and 1 per cent of water-soluble organic solvent. The process is applicable to any water-soluble cellulose ester, and particularly to water-soluble cellulose acetate, the solvent to be removed being acetic acid. The ester may be prepared by hydrolysis in a plurality of stages of cellulose acetate in the medium in which it has been prepared or of the precipitated and dried ester. It is particularly applicable to the further hydrolysis of "fines" obtained on filtering commercial acetone-soluble cellulose acetate which has been precipitated from solution. In an example 100 parts by weight of wet water-laden cellulose acetate fines are dissolved in glacial acetic acid containing 4 per cent sulphuric acid on the weight of cellulose acetate. The hydrolysis is carried out at 70 DEG C. with gradual addition of water for 20 hours, the acetyl value being reduced from 54 to 21 per cent (calculated as acetic acid). After neutralization of the sulphuric acid with magnesium acetate, the solution is counter-current extracted with isopropyl ether and the water-soluble cellulose acetate recovered by evaporation of the water or by precipitation with acetone or dioxane. If desired, the solution after extraction may be employed for the direct formation of films, foils and the like. Specification 568,047 is referred to.