Rheology of vegetable oil analogs and triglycerides

The rheological properties of two complex mixtures of short-chain triglycer ides were experimentally determined. Dynamic or absolute viscosities of the mixtures were measured for shear rates of 0.32 to 64.69 s(-1) at temperatu res between 25 and 80 degrees C. The compositions of the mixtures were base d on the oil of the plant species Cuphea viscosissima VS-320, a natural sou rce of short-chain triglycerides. The dynamic viscosities of these mixtures were compared to those of a traditional vegetable oil (peanut oil) and die sel fuel. The results of this comparison were used to make estimates of the performance of such triglyceride mixtures as diesel fuel substitutes, sinc e viscosity can be a key indicator of fuel performance for possible substit ute diesel fuels. The crystallization temperatures of these two mixture-wer e also determined experimentally, and the effects of crystallization on fue l performance were projected. Additionally, the dynamic viscosities of pure triglycerides from C6:0 to C18:0 at 75 degrees C were plotted vs. chain le ngth. These viscosities were measured at high shear rates (>6 s(-1)) where dynamic viscosity is shear-independent. An obvious trend in the relationshi p between triglyceride chain length and viscosity was observed. A second-or der regression was used to obtain an equation for this relationship. This e quation was used as a model for composition dependence of viscosity. This m odel was applied to the viscosities of the triglyceride mixtures examined h ere. There was good agreement between the model and the actual, measured vi scosity values determined in this study.