Simultaneous enhancement and percolation behaviors of damping and mechanical properties of ethylene–propylene–diene rubber by introducing phase-change organic acid

•The damping and mechanical properties of EPDM existed percolation thresholds of SA.•The percolation of damping was mainly due to solidlike–liquidlike transition.•The mechanical percolation was dependent on the increasing crystal SA.•We utilized the different properties of SA before and after phase-change happened.

Ethylene–propylene–diene rubber (EPDM)/stearic acid (SA) composites with improved strength and high damping performance were prepared by blending. With increasing SA content, the damping and mechanical properties of EPDM both quickly increased and there existed a percolation threshold of SA loadings, respectively. By analyzing the viscoelastic properties and cross-linking process of EPDM composites, it could be thought that the two percolations were attributed to two different cross-linked networks caused by phase-change organic acid, respectively. The percolation of damping performance coincides with that of liquidlike–solidlike transition of EPDM molecular chains, which was due to the decreasing cross-linking density, caused by restricting the decomposition of vulcanizing agent by SA, and enhanced the mobility of EPDM chains. The mechanical percolation was mainly dependent on the formation of a physical rubber–filler network by increasing crystal SA, which behaved as a filler before phase-change happened.