Xanthan/Carob interactions at very low concentration

Xanthan/carob interactions at very low concentration have been studied by viscosity measurements at 25°C and in 0.1 NaCl. The existence of a weak network structure, exhibiting thixotropic behavior, has been shown, down to reduced concentrations C[η] much lower than that corresponding to coil overlap. Maximum synergistic effects are observed for a xanthan/carob (X/C) ratio of 5.5/4.5. The formation of the network is dependent on the aging time, and for very dilute systems, a very low shear rate is necessary to observe a transitory network. From viscosity measurements after disruption of the structure under shear, the intrinsic viscosity and the apparent Huggins coefficient of several X/C mixtures have been determined. They show a decrease in the average hydrodynamic volume of the polymers and a high tendency to aggregation at X/C ratios corresponding to network formation. To take into account all the observed phenomena, a mechanism involving the formation of stable aggregates and of shear-sensitive ‘superaggregates’ is proposed.