Large amplitude oscillatory shear of xanthan gum solutions. Effect of sodium chloride (NaCl) concentration

Abstract

Large amplitude oscillatory shear (LAOS) results are shown to be useful to describe the mechanical behaviour of materials at large deformations, well beyond the linear viscoelastic region, which are closer to real processing conditions. We illustrate the applications of LAOS with xanthan gum aqueous dispersions at different NaCl concentrations, on account of the great technological interest in this bacterial polysaccharide. LAOS is shown to be much more sensitive than small amplitude oscillatory shear (SAOS) to the influence of NaCl concentration. This is illustrated by a complete rheological characterisation of the system by means of both full-cycle (average elastic modulus and dynamic viscosity) and local methods (strain-hardening and shear-thickening ratios). The different rheological behaviours observed were related to the microstructures of the xanthan gum molecules as a function of the NaCl content.