OSCILLATORY RHEOLOGY OF LENTIL STARCH/NANOCLAY BLEND SUSPENSION: APPLICABILITY OF TIME-TEMPERATURE SUPERPOSITION

The effect of incorporating montmorillonite nanoclay into lentil starch dispersion was studied by oscillatory rheological measurement. Rheological measurements were carried out at non-isothermal (40-95 degrees C) and isothermal (70-90 degrees C) condition. The elastic modulus (G) of starch/clay blend showed a significant improvement in the magnitude in the melt when clay concentration was at 5% wt or higher. The peak complex viscosity modulus (T-*max) decreased from 81.6 to 80.4 degrees C with increasing clay concentration during non-isothermal heating. The empirical principle of time-temperature superposition was tested to bring experimental dynamic rheological data at selected temperatures together into single master curves at a reference temperature of 80 degrees C. The complex viscosity (*) master curve was found to follow the rule with slight deviation. The elastic modulus superposition (G-) was found to fail in the temperature regime considered in this study. The failure of time-temperature superposition was believed to have happened due to complex starch-nanoclay-water matrix formation, temperature response of individual components, and phase change during gelatinization of starch.