GB637267A - Improvements in the manufacture of organic esters of cellulose - Google Patents

Abstract

Cellulose esters are manufactured by esterifying cellulose with the anhydride of a lower fatty acid in the presence of a solvent for the cellulose ester formed, using as catalyst during the esterification between 0.8 per cent and 10 per cent of sulphuric acid and between 0.2 per cent and 2 per cent of perchloric acid, both calculated on the weight of the cellulose. The lower fatty acid is an unsubstituted mono-carboxylic acid containing not more than 4 carbon atoms. Preferably the proportion of sulphuric acid used is about 0.8-6 per cent and of perchloric acid about 0.2 and 1.5 per cent. The solvent for the cellulose ester may be the esterifying acid and/or another solvent such as methylene chloride. The cellulose may be cotton, cotton linters, or a purified wood pulp having an alpha-cellulose content preferably above 90 per cent; it is preferably pretreated with lower fatty acid and perchloric or formic acid before esterification. After esterification the cellulose ester may be ripened. The production of esters with acetyl values of 57-58.5 per cent and 61-62.5 per cent is referred to in particular, and cellulose acetate, propionate, butyrate, acetate-propionate and acetate-butyrate are mentioned. In one example, cotton was pretreated with acetic acid and perchloric acid and added to a cooled mixture of acetic acid, acetic anhydride and sulphuric acid. After an hour aqueous acetic acid was added and the mixture ripened at 45 DEG C. for 22 hours (sulphuric acid may be added). The cellulose acetate obtained had an acetyl value of 57 per cent. In another example, cotton was pretreated with acetic acid and formic acid and added to a mixture of acetic anhydride, acetic acid, perchloric acid and sulphuric acid. After 2 1/2 hours aqueous acetic acid was added and allowed to stand for 1 hour at 50 DEG C. A cellulose triacetate of acetyl value above 62 per cent was produced. Specifications 531,014, 538,913, 566,863, 568,047, 568,098, 581,157, 597,295 and 620,726 are referred to.