Rheological properties of gum arabic solution: From Newtonianism to thixotropy

The influence of molecular association on the rheological behavior of gum arabic solution was studied. Using time-dependence of transient shear stress a reversible molecular association could be arrested and the thixotropy of gum arabic solution was interpreted. The structural breakdown, buildup and the effect of shear history due to molecular association could be related using the Casson's equation. Stress jump measurements distinguished the effect of molecular association on the elastic and viscous contributions of shear stress. An elastic-like contribution dominated at low shear rates whereas the viscous component became important at high shear rates. The elastic contribution was strongly affected by the molecular association of gum arabic, with increased molecular association contributing to a larger elastic contribution. The elastic and viscous contributions were also investigated in transient flow. Both of the contributions increased with rest time, indicating a buildup of molecular association. With increasing the rest time the elastic contribution increased much faster than the viscous contribution to the total stress. (C) 2010 Elsevier Ltd. All rights reserved.