Evaluation of viscosities of amorphous phases in frozen systems by WLF kinetics and glass transition temperatures

The viscosities of concentrated solutions of glucose, fructose, sorbitol and xylitiol were measured by a falling sphere method. The measured viscosities were compared with those predicted by WLF kinetics from glass transition temperatures. Discrepancies between measured and predicted viscosities were found to be within an order of magnitude of 0.3 on log E. Experimental data on sucrose solutions obtained from literature sources were also compared with WLF predicted values. The viscosities of the amorphous phases in frozen or partially frozen sucrose-, glucose-, fructose-, citric acid-, dimethyl sulfoxide-, polyvinylpyrrolidone- and glycerol-water systems were estimated by WLF kinetics and freezing temperatures. At equal sub-freezing temperature, the viscosities increased with the increasing of molecular weight. In addition, viscosity changes during devitrification and recrystallization of 60-70% sucrose solutions, which do not freeze upon cooling, were evaluated.