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.

Insights into the Payne Effect of Carbon Black Filled Styrene-butadiene Rubber Compounds

As a widely used reinforcing filler of rubber, carbon black(CB) often enhances the nonlinear Payne effect and its mechanism still remains controversial. We adopt simultaneous measurement of rheological and electrical behaviors for styrene-butadiene rubber(SBR)/CB compounds and CB gel(CBG) during large deformation/recovery to investigate the contribution of conductive CB network evolution to the Payne effect of the compounds. In the highly filled compounds, the frequency dependence of their strain softening behavior is much more remarkable than that of their CB network breakdown during loading, while during unloading the unrecoverable filler network hardly affects the complete recovery of modulus, both revealing that their Payne effect should be dominated by the disentanglement of SBR matrix. Furthermore,the bound rubber adjacent to CB particles can accelerate the reconstruction of continuous CB network and improve the reversibility of Payne effect. This may provide new insights into the effect of filler network, bound rubber, and free rubber on the Payne effect of CB filled SBR compounds.