Non-Newtonian flow behaviour of gellan gum aqueous solutions

Rheological properties of gellan gum solutions with and without salt have been monitored using oscillatory measurements and steady-shear viscosity measurements. The steady-shear viscosity measurements indicated that gellan gum solutions showed a wide Newtonian plateau when gellan gum molecules took a coil conformation, and that the shear-thinning behaviour became more conspicuous with conformational change of gellan gum molecules from coiled to helical, and the range of the Newtonian plateau became limited only to very low shear rates. When gellan gum solutions showed rheological behaviour as a dilute or concentrated polymer solution, these systems obeyed the Cox–Merz superposition of steady-state viscosity and dynamic viscosity. As gellan gum solutions formed a weak gel, the Cox–Merz rule was not valid; however, the deviation from this superposition was less significant than that of xanthan gum solutions which also show weak-gel behaviour. Received: 8 December 1998 Accepted in revised form: 5 March 1999