Steady shear and dynamic rheological properties of xanthan gum solutions in viscous solvents

Abstract

An extensive examination of the first normal stress difference and linear viscoelastic properties of xanthan gum solutions has been conducted in relation to molecular theories in the literature. The first normal stress difference, storage modulus, and loss modulus are reported for 0.01–0.04% w/w solutions of xanthan gum in high viscosity (wheat syrup and water) solvents. The average length of the xanthan molecules used was determined by light scattering to be (1.25±0.05)×103 nm. The storage and loss moduli obtained show a frequency dependence consistent with theories that included a relaxation time spectrum, while the first normal stress difference exhibits dependence on shear rate consistent with theories of suspensions of rigid particles. Both the first normal stress difference and the solute contribution to the storage modulus were found to vary linearly with concentration and with the solvent viscosity to the power of 2/3. Extensional viscosity measurements of a xanthan gum solution are in good agreement with the predictions for semi-dilute suspensions of rigid rods.