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RESEARCH PRODUCT

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

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The present study derives a fixed-concentration (0.4%) xanthan gum dispersion flow model for different molar concentrations of sodium chloride (0–0.25M) and different temperatures (20–70°C). The Ostwald–de Waele model is used in all cases. A temperature rise reduces the shear-thinning characteristics of the systems, although the power law index is much less sensitive 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 ≥0.15, and there are decreases in consistency upon raising the temperature in all cases. The viscous behavior of the dispersions is interpreted using the Eyring equation. The activation energy and the free volume decrease when the shear rate is increased. The addition of NaCl, regardless of the molar concentration involved, provokes an important decrease of the activation energy. The free volume is independent of the molar concentration of NaCl for molar values >0.025. These results are related to the structure of the dispersions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 332–339, 2002