Kinetic interpretation of influence of sodium chloride concentration and temperature on xanthan gum dispersion flow model

The present study derives a fixed-concentration (0.4%) xanthan gum dispersi on flow model for different molar concentrations of sodium chloride (0-0.25 M) and different temperatures (20-70 degreesC). The Ostwald-de Waele model is used in all cases. A temperature rise reduces the shear-thinning charact eristics of the systems, although the power law index is much less sensitiv e to changes in temperature when NaCl is added, even in very small amounts. The lowest consistency values correspond to the dispersions formulated in the absence of salt, the highest values are observed for molar values of gr eater than or equal to0.15, and there are decreases in consistency upon rai sing the temperature in all cases. The viscous behavior of the dispersions is interpreted using the Eyring equation. The activation energy and the fre e volume decrease when the shear rate is increased. The addition of NaCl, r egardless of the molar concentration involved, provokes an important decrea se of the activation energy. The free volume is independent of the molar co ncentration of NaCl for molar values >0.025. These results are related to t he structure of the dispersions. (C) 2002 John Wiley & Sons, Inc.