Shear rate dependence of the viscoelasticity of polymer solutions.: II. xanthan gum

Abstract

The shear rate dependent rheological properties of aqueous solutions of xanthan gum are measured. The steady flow viscosity is non-Newtonian and the oscillatory flow viscoelasticity is strongly dependent upon the amplitude of the shear rate as well as the frequency. A method for characterization and analysis of these nonlinear viscoelastic properties is described. The analysis is based upon a generalized Maxwell model in which the relaxation processes truncate in a manner dependent on the shear rate. The same relaxation processes are responsible for both the steady and the oscillatory flow behavior. With the xanthan gum solution at a concentration of 1000 ppm, the relaxation spectrum can be approximated by three discrete relaxation processes which have relaxation times of 0.531 s, 0.092s, and 0.0066 s. These three processes are sufficient to describe how the viscoelasticity changes with both shear rate and frequency and how the steady flow viscosity changes with shear rate.