Strain-induced crystallization of natural rubber/zinc dimethacrylate composites studied using synchrotron X-ray diffraction and molecular simulation

Natural rubber (NR) reinforced by in situ polymerization of zinc dimethacrylate (ZDMA) exhibits excellent mechanical properties. However, the corresponding reinforcement mechanism is still unclear. Using synchrotron wide-angle X-ray diffraction (WAXD) measurements, we observed that strain-induced crystallization of NR/ZDMA composites had a direct affect on the ultimate mechanical properties. An increase in ZDMA fraction resulted in a lower strain at the onset of crystallization. Further analysis revealed that three factors contributed to the reduction in onset strain, including higher whole cross-linking density due to the emergence of ionic cross-linking clusters, strain amplification of nanodispersion of poly-ZDMA (PZDMA), and the confinement effect of the filler network. The results of dynamic Monte Carlo simulation showed that the confinement effect of the filler network on chain segments favored segmental orientation in regions near the polymer-filler interface, thus inducing a decline in onset strain.