Superior fatigue and mechanical properties of ethylene-propylene diene monomer rubber incorporated with Zr-based metal-organic framework

This research reports the remarkable effects of Zr-based metal-organic framework, i.e. UiO-66, on cross-linked network structure and mechanical behaviors of ethylene-propylene diene monomer (EPDM) rubber under sulfur vulcanization systems. To this end, EPDM rubber was vulcanized with conventional (CV), semi-efficient (SEV) and efficient (EV) vulcanization systems. In addition, EPDM nanocomposites containing 5 phr UiO-66 with all three vulcanization systems were also prepared, for the sake of comparison with their corresponding unfilled samples. While the unfilled EPDM vulcanizates showed expectable behaviors in cross-linking density estimated by swelling experiment and cure-rheometer parameters based on their sulfur content and accelerator/sulfur ratio in each vulcanization system, CV cured EPDM/UiO-66 nanocomposite exhibited completely distinctive characteristics. The special swelling behavior plus exclusive cure kinetics supported by dynamic mechanical analysis led us to postulate a distinctive bimodal cross-linked network morphology including a highly cross-linked rubber shell around UiO-66 along with a lightly cross-linked rubber matrix for CV cured system. This special morphology was attributed to higher sulfur content of CV system which was supposed to be adsorbed by UiO-66 due to its tendency toward sulfur and sulfur containing chemicals. Superior tensile and fatigue properties of CV cured EPDM/UiO-66 were also explained by such morphological model.