GB737566A - Improvements in the production of organic acid esters of cellulose - Google Patents

Abstract

Cellulose is esterified with an organic acid anhydride in the presence of more than 350 per cent (on the weight of the cellulose) of methylene or ethylene chloride as solvent and sulphuric acid as catalyst, and the cellulose ester so produced is ripened by adding water to the primary esterification solution in amount sufficient both to hydrolyse residual acid anhydride and to provide water for the ripening reaction, neutralizing substantially all the sulphuric acid in the solution, removing by distillation a substantial proportion of the methylene or ethylene chloride (without reducing the methylene chloride content below 30 per cent or the ethylene chloride content below 50 per cent, on the weight of the cellulose), and then heating the solution to 100-190 DEG C. and maintaining it between these temperature limits until the desired degree of ripening has taken place. Preferably the amount of solvent distilled off is such as to leave in the solution between 30 and 150 per cent of methylene chloride or between 50 and 200 per cent of ethylene chloride. The process is applicable to the production of cellulose acetate, propionate, butyrate, and other organic acid esters of cellulose. The cellulose may be purified cotton linters, wood-pulp, pulp from straw or grasses, or a mixture of cotton linters and wood-pulp cellulose. During the process, so much of the solvent may be distilled off that the solution remaining has the form of a stiff plastic mass. The sulphuric acid may be neutralized by means of a carbonate, acetate, oxide or hydroxide of an alkaline-earth metal, zinc, or aluminium. If desired, the ripened solution may be thinned by the addition of acetic acid or acetone before the cellulose ester is precipitated. Specification 620,726 is referred to.