Determination of the optimal reaction conditions for the preparation of highly substituted carboxymethyl Cassia tora gum

Highly substituted carboxymethyl Cassia tora gum (CM-CTG) was prepared from CTG by treatment with monochloroacetic acid (MCA) in ethanolic aqueous solutions after alkalization under different reaction conditions. The influence of the etherification temperature, alkalization and etherification times, molar ratio of sodium hydroxide to MCA (nNaOH/nMCA), theoretical degree of substitution (DSt), and weight percentage of water (WH2O%) in the solution on the degree of substitution (DS) and reaction efficiency (RE) of the reaction were investigated. Optimum preparation conditions for a CM-CTG with DS of 1.05 are: etherification temperature, 60 °C; alkalization time, 60 min; etherification time, 180 min; nNaOH/nMCA, 2.1; DSt, 1.4; and WH2O%, 20%. Fourier-transform infrared analysis of the products indicated that carboxymethylation was successful. Rheological studies show that all the CM-CTG pastes are pseudoplastic fluids, and the shear sensitivity varies with DS. The degree of crystallinity of CM-CTG decreases with increasing DS, as shown by X-ray diffraction measurements.