Rheological behavior of uncured styrene-butadiene rubber at low temperatures, pure and filled with carbon black
Résumé
The flow behavior of an uncured styrene-butadiene rubber (SBR) has been studied by using a specific preshearing capillary rheometer in the range of temperatures encountered in extrusion, i.e. between 40°C and 90°C. A pure SBR and various SBR compounds filled with different amounts of carbon black (from 17 to 33 wt%) have been characterized. It was observed, for all tested materials, that the flow curve could be divided in different parts: at low shear rate, the material exhibits a classical behavior, where stress increases regularly with the shear rate. Above a certain critical stress, flow features changed, characterized by the simultaneous onset of wall slip and upstream instabilities. This critical stress is independent of temperature but increases linearly with carbon black amount. Flow curves at different filler contents were superimposed, using a shift factor that varies with filler content. Two theories for time/filler content superposition were proposed. Finally, a general viscosity law for uncured SBR compounds was introduced. This law is based on a Carreau-Yasuda equation, where zero-shear viscosity and characteristic time depend on both temperature and filler content, through Arrhenius and Krieger-Dougherty expressions, respectively.