GB608310A - Improvements in the production of cellulose esters - Google Patents

Abstract

A cellulose ester of an organic acid containing at least three carbon atoms is obtained by submitting cellulose to the action of the anhydride of the organic acid in presence of the organic acid itself and an esterification catalyst, incorporating a further quantity of the organic acid with the esterification mixture when esterification is nearly complete, allowing reaction to continue at least until the esterification mixture is substantially clear, and then precipitating the cellulose ester. The cellulose ester is precipitated in a fibrous open condition which facilitates the purification treatment. The organic acid may be propionic, butyric, or other aliphatic carboxylic acid, and the catalyst may be sulphuric acid. When the mixture has become clear, the dissolved cellulose ester may be submitted to a ripening treatment at elevated temperature. In the production of cellulose propionate, the esterifying medium may comprise 3-6 parts by weight, on the cellulose, of propionic anhydride, 0.2 to 1.0 parts by weight of propionic acid, and 0.01-0.09 parts of sulphuric acid. The cellulose may be pre-treated with a mixture of propionic acid, formic acid and sulphuric acid. The entire amount of propionic acid present during esterification is preferably added to the cellulose during the pre-treatment. Prior to charging the pre-treated cellulose into the esterification vessel, the mixture of anhydride, sulphuric acid, and propionic acid, if a further quantity of this is needed, is preferably cooled to -12 DEG to +5 DEG C. The temperature is permitted to rise during the esterification to a maximum of 20-38 DEG C. When the ester contains from 2.75 to 2.95 propionyl groups, the further addition of propionic acid is made, preferably in an amount of 1-5 times the weight of the cellulose. Esterification is allowed to continue for 1-4 hours or until the mixture is clear and free of fibres. Water is then added to destroy any excess of anhydride and to allow ripening to proceed. The sulphuric acid may then be neutralized by adding magnesium carbonate. The cellulose propionate is precipitated by the addition of water. The cellulosic material may be cotton, cotton linters, wood pulp, regenerated cellulose, grasses, straws, hulls or bagasse.