Elucidation of Kinetic and Symmetry Effects on the Viscosity and Flow Behavior of Stearic and Oleic Triacylglycerols

The flow behavior and viscosity of TAGs containing oleic and stearic acids were examined in the liquid phase as well as at temperatures close to the onset of crystallization by means of a temperature-controlled rheometer. Gelling and crystallization transitions were unambiguously identified by singularities in the viscosity versus temperature curves of the TAGs. An additional transition between the gelling and onset of crystallization temperatures, attributed to the reorganization of the gel, was observed in the symmetrical TAGs only. The effect of the cooling rate, ranging between 0.1 and 5° C/min, was investigated. The flow behavior of the studied TAGs was shown to be strongly determined by structural parameters (symmetry, degree of unsaturation). The flow behavior was also affected significantly by the cooling rate, suggesting that to certain extents the flow behavior determined by structural parameters could be changed by manipulating the cooling rate. The study confirmed that TAG crystallization is initiated by and depends, at least in part, on complex molecular short range order transformations occurring in the melt. The findings of the study may be valuable for evaluating systems and equipment that are involved in the storage, handling and processing of materials incorporating these TAGs.