PROCESS FOR FRACTIONATING AN ESTERIFIED CELLULOSE ETHER
A process for fractionating an esterified cellulose ether comprising groups of the formula —C(O)—R—COOH, wherein R is a divalent hydrocarbon group, comprises the steps of a) blending the esterified cellulose ether comprising groups of the formula —C(O)—R—COOH with an aqueous liquid and setting the temperature of the resulting blend to less than 10° C. to dissolve a portion of the esterified cellulose ether in the aqueous liquid, b) separating the non-dissolved portion of the esterified cellulose ether from the remainder of the blend, and c) recovering or disposing of the esterified cellulose ether that is dissolved in the aqueous liquid.
1 . A process for fractionating an esterified cellulose ether comprising groups of the formula —C(O)—R—COOH, wherein R is a divalent hydrocarbon group, which process comprises the steps of
a) blending the esterified cellulose ether comprising groups of the formula —C(O)—R—COOH with an aqueous liquid and setting the temperature of the resulting blend to less than 10° C. to dissolve a portion of the esterified cellulose ether in the aqueous liquid,
b) separating the non-dissolved portion of the esterified cellulose ether from the remainder of the blend, and
c) recovering or disposing of the esterified cellulose ether that is dissolved in the aqueous liquid.
2 . A process for preparing an esterified cellulose ether comprising groups of the formula —C(O)—R—COOH, wherein R is a divalent hydrocarbon group, which process comprises the steps of
a) reacting a cellulose ether with a dicarboxylic acid anhydride or with a combination of a dicarboxylic acid anhydride and an aliphatic monocarboxylic acid anhydride in the presence of an aliphatic carboxylic acid to produce a reaction product mixture comprising an esterified cellulose ether comprising groups of the formula —C(O)—R—COOH, precipitating the esterified cellulose ether from the reaction product mixture, blending the precipitated esterified cellulose ether with an aqueous liquid and setting the temperature of the resulting blend to less than 10° C. to dissolve a portion of the esterified cellulose ether in the aqueous liquid,
b) separating the non-dissolved portion of the esterified cellulose ether from the remainder of the blend, and
c) recovering or disposing of the esterified cellulose ether that is dissolved in the aqueous liquid.
3 . The process of claim 1 wherein step a) comprises setting the temperature of the resulting blend to a temperature of less than 8° C.
4 . The process of claim 1 wherein step a) comprises setting the temperature of the resulting blend to a temperature of less than 5° C.
5 . The process of claim 1 wherein step a) comprises blending the esterified cellulose ether with the aqueous liquid at a weight ratio of from 5 to 100 weight parts of aqueous liquid per one weight part of esterified cellulose ether.
6 . The process of claim 1 wherein in step c) the esterified cellulose ether is recovered by heating the aqueous liquid comprising dissolved esterified cellulose ether to a temperature of at least 30° C. or by freeze-drying.
7 . The process of claim 1 wherein the esterified cellulose ether comprises groups of the formula —C(O)—CH 2 —CH 2 —COOH.
8 . The process of claim 1 wherein the esterified cellulose ether additionally comprises aliphatic monovalent acyl groups.
9 . The process of claim 1 wherein the esterified cellulose ether is hydroxypropyl methylcellulose acetate succinate.
10 . The process of claim 1 wherein an esterified cellulose ether having a weight average molecular weight M w of at least 80,000 Dalton and a Polydispersity M w /M n of not more than 2.6 is obtained in step b).
11 . The process of claim 1 wherein an esterified cellulose ether having a weight average molecular weight M w of up to 70,000 Dalton and a Polydispersity M w /M n of not more than 2.6 is obtained in step c).
12 . An esterified cellulose ether obtainable from step b) of the process of claim 1 .
13 . The esterified cellulose ether of claim 12 ,
i) having a weight average molecular weight M w of at least 80,000 Dalton, and
ii) having a Polydispersity M w /M n of not more than 2.6.
14 . An esterified cellulose ether obtainable from step c) of the process of claim 1 .
15 . The esterified cellulose ether of claim 14 ,
i) having a weight average molecular weight M w of up to 70,000 Dalton,
ii) having a Polydispersity M w /M n of not more than 2.6, and
iii) of which at least 85 wt. % of the esterified cellulose ether is soluble in a mixture of 2.5 weight parts of the esterified cellulose ether and 97.5 weight parts of water at 5° C.