Steady and oscillatory shear behavior of fluid gels formed by binary mixtures of xanthan and gellan

Abstract

The rheological properties of xanthan–gellan binary fluid gels at a total concentration of 0.1 wt% were compared with individual xanthan and gellan solutions. Under steady shear, xanthan solutions showed a zero-shear viscosity and shear-thinning behavior that was adjusted to the Carreau model. In the absence of added salts, gellan solutions exhibited Newtonian behavior. Addition of monovalent and divalent salt to gellan induced strong non-Newtonian behavior with the appearance of a yield stress, thixotropy and a high degree of shear-thinning behavior that confirm the typical properties of ‘fluid gels’. Upward and downward curves were adjusted to the Herschel–Bulkley model. From dynamic tests, xanthan with and without salt and gellan without salt showed fluid-like behavior, while gellan solutions with salt exhibited gel-like behavior. The high sensitivity of gellan to counter ions offers the possibility of getting different rheological behaviors depending on ion concentration and proportion of components in the mixture.