| abstract |
The process for preparing mixed cellulose ethers proceeds in the following steps: (a) alkalizing of the cellulose, (b) etherifying of the alkali cellulose in the presence of a base by using at least one etherifying agent which requires, for the reaction with cellulose, a catalytic and sub-stoichiometric quantity of a base, and (c) increasing the quantity of base, and (d) etherifying the cellulose ether so prepared by using at least one etherifying agent which requires, for the reaction with cellulose, an at least stoichiometric quantity of a base or a catalytic and substoichiometric quantity of a base, increased over the quantity used in (a), with at least one inert organic solvent being used as a dispersing auxiliary in at least one of the steps and water being present in all steps, wherein mixed etherification leads to a water-soluble product and dimethoxyethane, an alkanol, an alkanediol and/or an alkoxyalkanol are used as the organic solvents. The process serves, in particular, for the preparation of methyl-hydroxyethyl cellulose or methyl-hydroxypropyl cellulose. |