Rheological characteristics of concentrated ternary gum mixtures with xanthan gum, guar gum, and carboxymethyl cellulose: Effect of NaCl, sucrose, pH, and temperature.

Our goal was to investigate the effects of various conditions of media (NaCl, sucrose, pH, and temperature) on the steady and dynamic shear rheological properties of a concentrated ternary gum mixture system (1.0 wt%) containing xanthan gum (XG), guar gum (GG), and carboxymethyl cellulose (CMC). Regardless of the media conditions, all gum mixtures exhibited a high shear-thinning behavior with a low flow behavior index (<0.30). NaCl addition resulted in a decrease in the consistency index (K, 32.8-16.1 Pa·sn) and apparent viscosity at 50 s-1 (ηa,50, 1.00-0.75 Pa·s), as well as the elastic modulus (G') and viscous modulus (G″) due to the charge screening effect. Similar result was observed with an increase in acidity of media. The presence of sucrose also induced the decrease in the ηa,50, K, G', and G″ values of the ternary gum, but tan δ (G″/G') decreased, indicative of higher weak gel-like properties. No effect of NaCl or sucrose addition on the temperature dependence of G' values was observed, whereas pH adjustment was impacted. These results demonstrated that the presence of co-solute, the acidity of media, and temperature influenced the rheological properties of ternary gum, and in particular acid condition gave a great impact.

Effect of CMC addition on steady and dynamic shear rheological properties of binary systems of xanthan gum and guar gum.

The effect of CMC on the steady and dynamic shear rheological properties of binary mixtures of XG and GG was examined at different mixing ratios. All XG-GG-CMC ternary mixtures had high shear-thinning behavior and the n value of the sample with 5% CMC was the smallest compared with those of other samples. A marked increase in K and ηa,50 values was observed for ternary mixtures at a lower content (5%) of CMC, indicating that the synergistic interactions of the XG-GG binary mixture were affected by the content of CMC. The effect of temperature on the ηa,50 was well described by the Arrhenius equation for all samples. The activation energy values of all ternary gum mixtures are higher than that of binary gum mixture, and these values also decreased with an increase in CMC content from 5 to 15%. The dynamic moduli of ternary gum mixtures decreased with an increase in CMC content. The tan δ value of the ternary gum mixture with 5% CMC was much lower than those of other ternary mixtures. In general, these results suggest that the flow and dynamic shear rheological properties of XG-GG binary mixtures are strongly influenced by a small addition of CMC.