GB449066A - Improvements in method of making organic esters of cellulose - Google Patents

Abstract

A mixture comprising an unripened organic ester of cellulose in solution in a solvent consisting substantially of an aliphatic acid but containing water sufficient for ripening is subjected to distillation so as simultaneously to remove aliphatic acid and ripen the cellulose ester. Esters of high clarity and stability are obtained and lead to the production of high tenacity filaments, and films. Cellulose acetate, propionate, and butyrate are specified. The amount of water added to the esterification mixture is sufficient to hydrolyse remaining anhydride and ripen the cellulose ester, e.g. to acetone solubility. The proportion of water added may be 20--30 per cent based on the weight of cellulose. The proportion of aliphatic acid may be 7--10 times the weight of cellulose. Distillation may be effected at reduced pressure. Air or other gas may be injected to assist distillation. The cellulose ester may be precipitated by addition of water or other non-solvent. At the end of the esterification, acid catalyst may be reduced by addition of carbonate, bicarbonate, or acetate. Neutralization of mineral acid may be effected progressively during distillation. The aliphatic acid may or may not be that corresponding to the anhydride. Mixtures of catalysts such as sulphuric and hydrochloric acids, zinc chloride, and methyl chloride may be used. A further quantity of aliphatic acid may be added to the esterification mixture just prior to distillation in order to reduce the proportion of catalyst. In an example, cotton linters are acetylated at room temperature with a mixture of acetic anhydride, glacial acetic acid and sulphuric acid. After acetylation is complete water is added and the mixture is distilled under reduced pressure, sodium acetate being added in small quantity as the acetic acid distils, to reduce the proportion of sulphuric acid. Before all the acetic acid has been removed, the distillation is stopped and the cellulose acetate is precipitated by adding water to the mixture. The Specification as open to inspection under Sect. 91 specifies also the application of the process to the manufacture of cellulose formate. This subject-matter does not appear in the Specification as accepted.