GB742034A - Improvements in the manufacture of cellulose esters - Google Patents

Abstract

Cellulose is subjected to esterification with at least one anhydride of a lower fatty acid, containing 2-4 carbon atoms in the molecule, and sulphuric acid as catalyst so that the cellulose ester is formed in solution, and the cellulose ester is partially hydrolyzed while in solution. The partially hydrolysed cellulose ester still in solution is submitted to esterification under substantially anhydrous conditions with a dicarboxylic acid anhydride at an elevated temperature in the presence of at least one lower fatty acid, containing 2-4 carbon atoms in the molecule, as solvent and alkali metal acetate. Substantially anhydrous conditions in the bath for the second esterification may be obtained by adding to the bath an anhydride of a fatty acid containing 2-4 carbon atoms in the molecule. Preferably, any inorganic acid is neutralized before the final esterification by adding an excess of alkali metal acetate. The cellulose may be reacted with acetic anhydride and acetic acid using sulphuric acid as catalyst or a mixed ester may be obtained by adding propionic or butyric acid or anhydride to the acetylation mixture. The partial hydrolysis may be effected by adding aqueous acetic acid until the concentration of lower fatty acid is reduced to 80-95 per cent, and allowing the mass to stand for the desired time at an elevated temperature, e.g. 100-150 DEG F. When the hydrolysis has been carried out to the desired extent, there is added an alkali metal acetate or that compound may be formed in the mixture by adding sodium or potassium carbonate or hydroxide. Preferably, there should be 0.1 to 3 parts of sodium acetate in the esterification mass, per part of cellulose, over and above that used for neutralizing the sulphuric acid. If desired some or all of the alkali metal acetate may be added prior to completion of the hydrolysis. Dicarboxylic anhydride and an anhydride of a lower fatty acid are added and the mass may then be maintained at 140-212 DEG F. until the desired dicarboxylic acid radical content has been introduced into the cellulose ester. Cellulose mixed esters containing acetyl, propionyl or butyryl, and phthalyl, succinyl or maleyl radicals may be obtained. In an example, the production of cellulose acetate phthalate containing an acetyl content of 26 per cent and a phthalyl content of 26 per cent is described. The mixed ester is readily soluble in dilute sodium carbonate and in ammonia water. Specification 552,135 is referred to.