Relationships between mastication conditions and rheological behavior of a natural rubber

The mastication of natural rubber results in the shortening of the long molecular chains, which affects the viscosity of the material. Mechanical and thermo-oxidative breakdowns are the two major factors that interfere during mastication and processing of natural rubber. In an attempt to characterize the viscous behavior of a such product during processing, rheological properties of unvulcanized rubber are studied with a capillary rheometer and a parallel plate rheometer, in small amplitude oscillatory shear. An investigation is carried out with an internal mixer to determine the effect of mastication and temperature on the rheological properties. The influence of thermomechanical effect is quantified as a function of the specific energy and mastication temperature. Depending on mastication conditions, the variation of viscosity may be important and its decrease is quantified by integrating the specific energy and the mastication temperature in a Carreau-Yasuda model.