Abstract

Recycling of ethylene propylene diene monomer (EPDM) rubber has attracted increasing attention as an effective strategy to reduce rubber waste while maintaining material performance. In this study, waste EPDM was devulcanized through a thermomechanical process and incorporated into peroxide-crosslinked EPDM (PO-EPDM) composites to evaluate its applicability as a recycled rubber component. The recycled EPDM (rEPDM) content was varied from 5 to 25 phr, and its effects on devulcanization behavior, revulcanization characteristics, mechanical properties, compression set, and morphology were systematically investigated. Horikx analysis confirmed that the optimized thermomechanical process preferentially promoted sulfur crosslink scission while minimizing polymer main-chain degradation. As the rEPDM content increased, the minimum and maximum cure torques gradually decreased, indicating improved processability but reduced crosslink density after revulcanization. Tensile strength, tear strength, and compression set remained comparable to those of the virgin compound when the rEPDM content was 15 phr or lower. However, at 20 phr and above, significant deterioration in mechanical performance and elastic recovery was observed due to reduced interfacial adhesion, particle agglomeration, and heterogeneous crosslink structures, as confirmed by scanning electron microscopy. These results demonstrate that devulcanized rEPDM can be effectively incorporated into PO-EPDM without significant performance loss up to 15 phr, providing a practical guideline for manufacturing high-performance recycled EPDM materials with improved sustainability.

Keywords: Thermomechanical devulcanization, Recycled EPDM, Peroxide crosslinking, Revulcanization kinetics, Selective crosslink scission