Xanthan Stability at Elevated Temperatures

Summary Xanthan stability is examined to define more clearly the polymer's temperature limitations as a mobility-control agent. Experiments were performed to probe the relative importance of hydrolysis, oxidation, and helix-coil transitions in xanthan degradation. In the absence of oxidizing agents (i.e., dissolved oxygen), results indicate that free-radical, oxidation/reduction reactions are not the dominant mechanism for xanthan degradation. Depending on the pH, acid-catalyzed hydrolysis and base-catalyzed fragmentation reactions may play important roles. With Arrhenius calculations, it was estimated that under ideal conditions (no dissolved oxygen, pH 7 to 8, and moderate to high salinities), a xanthan solution could maintain at least half of its original viscosity for a period of 5 years if the temperature does not exceed 75 to 80°C [167 to 176°F], New polymers will be needed for chemical floods where xanthan does not have sufficient stability.