Studies on the synthesis and characterization of carboxymethylcellulose

Carboxymethylcellulose (CMC) was prepared in a completely heterogeneous procedure in an isopropanol/water slurry and the influence of the reaction conditions on the pattern of functionalization within the anhydroglucose repeating unit as well as due to the formation of the four main repeating units (i. e. unfunctionalized, mono-, di-, and tricarboxymethylated) was checked. The concentration of aqueous sodium hydroxide solution, which is used to activate the cellulose, was varied in the range from 8 to 30% at reaction times from 2 to 6 h at 55°C. The reaction with sodium monochloroacetate leads to the highest degree of substitution (DS_CMC) of 1.24 at a NaOH concentration of 15% and 5 h reaction time. Using a lye concentration of 30%, no influence of the reaction time between 2 h and 6 h was found. From ¹H NMR spectroscopical studies it was concluded that both the concentration of the alkali hydroxide solution and the reaction time influence the partial DS_CMC at positions O-2 and O-6, while position O-3 shows the lowest reactivity in any case, independent of the reaction conditions used. With increasing lye concentration, carboxymethylation occurs preferably at O-6. Information about the content of the differently functionalized repeating units can be obtained by chromatographic analysis after complete depolymerization of the polymer chains. Surprisingly, in any product synthesized a statistic content of the building units of the polymer was found even at low activation of cellulose.