Temperature Dependency of Gum and FILLED RUBBER Compounds IN the 40 – 180 °C Range

Time and temperature dependencies of modulus and other (rheological) functions are particularly important for polymer systems because, in the former case they allow understanding how a given polymer behaves over a large time span, and in the latter case, they position the material with respect to both its usage and processing windows. Rubber materials are generally amorphous polymers (with the notable exception of Natural Rubber and a few rare synthetics), so that in the room temperature range, they are on their rubbery plateau. Therefore, whilst they are generally processed above 100°C, no phase change occurs during processing contrary to most thermoplastics. It follows that the (temperature) processing window of elastomers coincides with their usage window. With respect to processing, temperature rather than time dependency is of importance for rubber materials. There are several manners to consider temperature dependency and, for polymer materials, the Arrhenius and the Williams, Landel and Ferry (WLF) models are the most common approaches. The former has received a theoretical background inspired by the Eyring’s fluid theory, with the concept of activation energy, and the latter has its root in the time-superposition principle. Providing the adequate test protocols and data treatment are used, modern computer control rheometers allow the temperature dependency of rubber materials to be routinely assessed, in a quasi automatic manner. The paper describes several such test protocols developed for the Rubber Process Analyzer RPA 2000® and the associated data treatments to document the effect of temperature in the 40 – 180°C range on several gum rubbers and a few (unaccelerated) carbon black filled compounds. The Arrhenius and the WLF approaches are then compared through the activation energy at 100°C.