Compared abilities of filled and unfilled natural rubbers to crystallize in a large strain rate domain

Strain induced crystallization (SIC) in filled and unfilled natural rubbers is investigated through in¿situ wide angle X-rays scattering (WAXS) experiments at various strain rates. The values of local stretching ratio at SIC onset (¿c,local) are found similar between filled and unfilled rubbers stretched at slow strain rate (10-3 s-1) and in a large temperature range [21 °C, 80 °C]. This is consistent with the fact that the calculated ‘local’ network densities of the first chains involved in SIC are very close in all samples. Conversely, ¿m,local for tests carried out in a large temperature range [21 °C, 80 °C] is found higher in filled samples compared to unfilled one due to a lower crystallites size. In order to investigate SIC in filled and unfilled rubbers submitted to conditions of solicitations met in pneumatic tires, in¿situ WAXS experiments are performed during high strain rates cycles (10–100 s-1) thanks to a recent homemade machine. By increasing the frequency, strong self-heating related to filler-rubber interaction causes a dramatic fall of the crystallinity index (CI) in filled rubber.