High-temperature Thermo-oxidative Aging of Vulcanized Natural Rubber Nanocomposites: Evolution of Microstructure and Mechanical Properties

The aging of natural rubber (NR) at high temperatures will seriously affect its service lifetime in many key applications. In the present work, the changes in microstructure and mechanical properties of semi-efficient vulcanized NR/carbon black (CB) vulcanizates during thermo-oxidative aging at high temperatures (150–200 °C) and a moderate temperature (95 °C) were compared. At high temperatures, a two-stage aging behavior, which was characteristic of a first rapid decline and then a continuous rise in the crosslinking density ( v e ), was identified and was found to be closely related to the depletion behavior of antioxidants. The surface cracking behavior observed in the second stage of high-temperature aging was discussed in terms of the grafting reaction of macromolecular radicals on CB particles and thermal expansion. In contrast, the aging of NR at moderate temperatures was much mild, which featured a continuous increase in v e and an oxidation mechanism dominated by peroxy radicals attacking double bonds. In general, the mechanical properties of NR vulcanizates during high-temperature aging depended on the competition effects of structural evolution in the crosslinked network and oxidation-induced chain scission.