GB578504A - Improvements in the production of cellulose esters - Google Patents

Abstract

A mixed organic ester of cellulose is obtained by subjecting cellulose to the action of an esterification medium comprising two different carboxylic acids, the anhydride of one of these acids, and an esterification catalyst, until esterification is substantially complete, then incorporating in the medium the anhydride of the other acid and an additional amount of catalyst and completing the esterification. The cellulose may be cotton, cotton linters, wood pulp, regenerated cellulose, or cellulose from grass, straw, bagasse, or other waste material. The catalyst may be perchloric acid, sulphuric acid, a mixture of hydrochloric acid and zinc chloride, or other mineral acid catalyst. The ester may be ripened by incorporating water with the solution in an amount in excess of that required to destroy residual anhydride and allowing the solution to stand until the required reduction in ester content has been effected. Prior to ripening some or all of the catalyst may be rendered inactive, e.g. by adding hydrated magnesium acetate, zinc acetate, aluminium acetate, aluminium chloride or calcium acetate. When sulphuric acid has been used as esterification catalyst, any sulphuric acid combined with the cellulose may be removed by adding water and allowing the solution to stand, if desired at a temperature lower than that at which hydrolysis of the organic acid radicals present in the ester is produced, e.g. below 25 DEG C. The cellulose ester is precipitated by mixing the solution with a large amount of water. The clarity of the product is improved if acetone, dioxane, methyl acetate, methyl or ethyl alcohol, or other inert solvent for the ester is added to the solution prior to precipitation. Cellulose acetate-butyrates, or propionate-butyrates may be obtained. In the production of cellulose acetate-butyrate, the cellulose may be pretreated with a mixture of acetic and butyric acids for several hours at 12-60 DEG C. The mixture is then cooled and butyric anhydride and an esterification catalyst are added. Esterification is preferably carried out so that the temperature does not rise above 30 DEG C. When the esterification is substantially complete, a mixture of acetic anhydride and additional catalyst is added. The mixture is allowed to stand until a clear solution is obtained.