Carboxymethyl tara gum (CMTG) was synthesized from the reaction between tara gum (TG) and monochloroacetic acid (MCA) in the presence of sodium hydroxide. The modification reaction was optimized in terms of the MCA/NaOH ratio, reaction time and temperature evaluated for degree of substitution (DS). The etherification was confirmed by FTIR and 13C NMR spectroscopy, and it was characterized by different analyses. After carboxymethylation, CMTG showed new bonds at 1592, 1413 and 1320 cm-1 by FTIR and a new peak at δ = 178 ppm by 13C NMR in response to the insertion of the carbonyl group. The microscopy showed higher degradation on the surface of the CMTG particles, and XRD indicated low crystallinity of the CMTG. Static light scattering demonstrated a reduction in the molar mass of tara gum after carboxymethylation. Thermal analysis (TGA and DSC) revealed a lower thermal stability of carboxymethylated gum compared to that of unmodified gum. Despite the insertion of negative charges demonstrated by the potential-zeta, CMTG and TG presented pseudoplastic behavior according to the rheological analyses, and CMTG presented lower viscosity at the concentrations that were studied.
Keywords: Carboxymethylation; Galactomannan; Rheological properties; Seed gum.
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