GB538959A - Improvements in the production of cellulose esters - Google Patents

Abstract

538,959. Cellulose esters. BRITISH CELANESE, Ltd. Feb. 21, 1940, Nos. 3274 and 3275. Convention dates, Feb. 28, 1939, and March 24, 1939. [Class 2 (ii)] The stability to light and heat of a ripened cellulose ester of an organic carboxylic acid is improved by forming a solution of the ester, after its isolation from the acidylation mixture, in a solvent containing a small concentration of sulphuric or phosphoric acid and reprecipitating the ester after the improvement in stability has been effected. The concentration of the acid is such that no substantial hydrolysis or change of solution viscosity of the cellulose ester takes place before reprecipitation. Prior to the precipitation from the acidylating mixture, the cellulose ester may be treated with a basic salt, e.g. basic aluminium acetate, sodium aluminate, or sodium acetate or a mixture of one of these salts with hydrochloric acid, aluminium chloride or zinc chloride. The solvent should contain but little if any water in order to avoid hydrolysis of the cellulose ester. Lower aliphatic acids such as acetic, propionic, or butyric acid, may be used as solvents. The process is applicable to the stabilization of secondary acetone-soluble cellulose acetate. The stabilization may be effected at 20-25‹ C. for several hours. Cellulose acetate precipitated from an esterification solution to which a basic salt has been added may be stabilized by dissolving it in acetic acid containing from 0.05-0.2 per cent of phosphoric acid (85 per cent), or containing 0.025-0.25 per cent of sulphuric acid (98 per cent). The products obtained have substantially the same acetyl value and acetone viscosity as before treatment but their stability to light and heat is greater. In the production of the cellulose esters there may be used as cellulosic material, cotton, cotton linters, wood pulp, or regenerated cellulose. The esterifying agent may be formic acid, acetic anhydride, propionic anhydride, butyric anhydride, or a mixture of anhydrides. The esterification catalyst may be sulphuric acid, sodium bisulphate, methyl sulphate, or a mixture of these with each other or with other catalysts such as zinc chloride. The cellulose esters obtained by the process may be used in the production of artificial filaments, staple fibre, bristles, straw, foils, films, plastics, and moulding compositions. Specification 447,530 is referred to.