GB571010A - Improvements in the production of organic esters of cellulose - Google Patents

Abstract

Cellulose esters of organic acids, obtained by esterifying cellulosic material with an organic acid anhydride in the presence of sulphuric acid as catalyst, are subjected to a preliminary ripening in solution in the presence of sulphuric acid, after which they are precipitated, redissolved, and then further ripened in solution in presence of an aliphatic polycarboxylic acid in an amount between 0.1 and 5 per cent of the original cellulose. Cellulose material such as cotton, cotton linters, wood pulp, regenerated cellulose, or cellulose from grasses, straws, or hulls, may be employed. The cellulose may be pretreated with acetic or formic acid, or a mixture of these acids, with or without sulphuric acid. The polycarboxylic acid used for the ripening may be a saturated or unsaturated compound, and it may contain substituents such as hydroxyl groups or halogen atoms. Oxalic, malonic, succinic, dibromo-succinic, glutaric, maleic, fumaric, malic, tartaric, aconitic, tricarballylic, or camphoronic acid may be used. When esterification is completed, the excess of anhydride is destroyed by adding water, and the cellulose ester is allowed to ripen in solution in presence of water and all or part of the sulphuric acid used as catalyst. This first ripening may be carried out until a cellulose acetate of acetyl value of 56.0 to 58.5 per cent calculated as acetic acid is obtained. The cellulose ester is then precipitated by adding water and is well washed. It is redissolved in aqueous acetic acid or other solvent and then an aliphatic polycarboxylic acid is added. The second stage of ripening is then carried out. The ripened ester is precipitated by adding water. The cellulose ester obtained has a high degree of stability and may be employed directly without any further stabilizing treatment. The process is applicable to the treatment of cellulose acetate, propionate, butyrate or other cellulose ester.