EFFICIENT PROCESS OF PREPARING AN ESTERIFIED CELLULOSE ETHER

An esterified cellulose ether is produced in a highly efficient manner in a process for reacting a cellulose ether with an aliphatic monocarboxylic acid anhydride and a dicarboxylic acid anhydride, wherein the process comprises the steps of a) preparing a reaction mixture comprising the cellulose ether, the aliphatic monocarboxylic acid anhydride and the aliphatic carboxylic acid such that the molar ratio of aliphatic carboxylic acid to anhydroglucose units of cellulose ether is up to 9.0:1 and heating the reaction mixture to a temperature of from 60° C. to 110° C. prior to, during or after mixing the components of the reaction mixture, and b) keeping the reaction mixture at least 15 minutes at the temperature of from 60° C. to 110° C. before adding dicarboxylic acid anhydride to the reaction mixture.