Work

Structure–property relationships in microwave-assisted carboxymethylated tara gum: Balancing substitution, molecular degradation, and rheology

Year: 2026

Type: article

Abstract: ABSTRACT Carboxymethylated tara gum (CMTG) is an anionic galactomannan whose macroscopic behavior depends on the interplay between degree of substitution (DS), molecular degradation, and charge density. In this work, a rapid microwave-assisted carboxymethylation strategy was developed and optimized using response surface methodology and compared with a conventional reflux etherification method. Microwave irradiation enabled reproducible substitution levels close to unity (DSCM ≈ 1.0) within 20 min, compared with 3 h under reflux conditions, but simultaneously promoted significant alkaline-induced chain fragmentation. Spectroscopic analyses (FTIR, ¹H and ¹³C NMR) confirmed successful etherification, whereas SEC analysis revealed multimodal molecular weight distributions with substantial low-molecular-weight fractions generated under microwave processing. Rheological analysis demonstrated that carboxymethylation markedly reduced the zero-shear viscosity (η₀) from 6.55 Pa·s for native tara gum to 0.59–1.99 Pa·s for CMTG derivatives, together with a reduction in relaxation time (λ) from 0.62 to 0.18 s, indicating decreased chain entanglement and faster structural relaxation. Despite this molecular fragmentation, highly substituted microwave-synthesized CMTG exhibited pronounced shear-thinning behavior, improved water solubility, and enhanced viscoelastic responsiveness associated with electrostatic chain expansion and charge-induced intermolecular interactions. Overall, microwave-assisted carboxymethylation provides a rapid and tunable route to engineer galactomannans with controllable substitution, molecular architecture, and rheological response for potential thickening, stabilization, and delivery applications.

Source: Materials Today Communications

DOI: 10.1016/j.mtcomm.2026.115545