Viscosity of xanthan gum solutions at low shear rates.

The viscosity of xanthan gum solutions in the low shear region was investigated with the aid of a Couette instrument. All solutions were highly pseudoplastic . Solutions containing 0.3-0.5% of the gum exhibited a highly ordered phase at very low shear. Viscosity, the degree of pseudoplasticity , and the value of the transition from soft gel to pseudoplastic behavior were directly related to gum concentration. The effect of the addition of a salt on viscosity depended on the xanthan gum concentration. The viscosity of a 0.3% xanthan gum solution was practically unaffected by the salts. Higher gum concentrations exhibited a viscosity increase when salt was present. Concentrations less than 0.3% exhibited a viscosity decrease in the presence of a salt. All viscosity effects seemed to reach limiting values at approximately 10(-3) to 3.3 X 10(-3) N salt. No major differences were observed between sodium chloride, calcium chloride, and sodium citrate in their influence on xanthan gum viscosity.