Guidelines for the rheological characterization of biodiesel

The rheological characterization of biodiesel at low temperatures is discussed. Gelling typically occurs in this range, and consequently the mechanical behavior becomes viscoplastic. We illustrate that the rheology of the gelled biodiesel is a strong function of the shear and thermal histories, and due to this dependence the testing conditions must be determined prior to the execution of a rheological measurement. We describe in detail how to determine these conditions by means of the thermal cycle test. Finally we present flow curves for different temperatures, to further illustrate the impact of gelling on the biodiesel rheology. We also discuss an important source of specious data that seems to be often overlooked in the literature.