The rheology and processability of tire compounds

The purpose of the work reported here was to define the parameters, which affect the rheology of tire compounds as well as their processability. Rheology was characterized over a wide range of shear rates. Processability was defined inversely as the roughness of the extrudate from the Monsanto Processability Tester (MPT) capillary rheometer. The roughness was measured by using image analysis of the extrudate surface contour. A good correlation was found between the extrudate roughness and the size of the Mooney peak (peak in apparent stress plotted against time for very small sheer rates in a start-up flow experiment). The Mooney peak can be represented as a yield stress. The effects of storage time and temperature on the size of the Mooney peak (i.e., its increase as a function of storage time) was studied. The kinetics of degradation of processability was not found to follow an Arrhenius type of behavior. Finally, a physical descriptive model was proposed to represent filler-rubber structures.