Microstructure Evolution and Strain Softening of Carbon Black Filled Natural Rubber Vulcanizates

Incorporation of carbon black (CB) in natural rubber (NR) enhances the Mullins effect and Payne effect of their vulcanizates, but the strain softening mechanisms and the microstructure evolution in the vulcanizates have not been clearly concluded so far. We investigate the Mullins effect and Payne effect of CB filled NR vulcanizates by using cyclic tensile tests at different temperatures and dynamic rheological measurements combined with simultaneous electric conduction. During cyclic stretching, the normalized recovery hysteresis energy and accumulative softening energy for NR/CB vulcanizates with different loadings can be both superimposed on a master curve, indicating that the Mullins effect is mainly dominated by the rubber matrix. The irreversible simultaneous resistance evolution also reveals that the structural evolution of nanoparticles (NPs) network is not directly related to the Mullins effect. Moreover, the extension of linear viscoelastic region and the hysteresis of Payne effect for filled vulcanizates subjected to cyclic stretching indicate the destruction of CB aggregated structure and the interfacial layers between CB and rubber chains during cyclic stretching. This investigation would be illuminating for the microstructure evolution and strain softening of rubber nanocomposites under harsh service conditions.