Strain-induced crystallization of carbon black-filled natural rubber during fatigue measured by in situ synchrotron X-ray diffraction

Natural rubber (NR) exhibits great fatigue properties which are usually explained by its ability to crystallize under strain. Nevertheless, strain-induced crystallization of NR in fatigue has never been investigated. We perform original in situ fatigue tests during which the degree of crystallinity, and the number and volume of crystallites are measured by synchrotron wide angle X-ray diffraction. For all loading conditions, the number of crystallites is constant. The evolution of their volume depends on the minimum stretch ratio achieved at each cycle. The results show that cyclic loading conditions modify the macromolecular structure of the material, in particular of its amorphous phase.