Oxidative degradation of crosslinked EPDM elastomers: Impact on the entanglement network

ABSTRACT The mechanical behavior of elastomers is mainly governed by the architecture of their macromolecular network. The increase in modulus observed during the oxidation of elastomers that predominantly undergo cross‐linking rather than chain scission can be described using the classical rubber elasticity theory. However, when chain scission becomes the main degradation process, the applicability of this theory may be questioned. This study investigates the relationship between the macromolecular network and the mechanical behavior of unfilled amorphous peroxide‐cured EPDMs by considering both the chemical cross‐link network and the physical entanglement network. The elastomers were characterized by equilibrium swelling and uniaxial tensile tests performed on unaged samples with different cross‐linker contents, as well as on oxidized samples exposed at 75°C, 90°C, and 100°C. Results clearly show that varying the cross‐linker content affects only the chemical cross‐link network without altering the entanglement density, whereas oxidation modifies both the chemical and entanglement networks. These findings provide new insights into the interplay between chemical cross‐links and physical entanglements during oxidation and highlight the limitation in using rubber elasticity theory when chain scission dominates the degradation process. They also emphasize the critical role of entanglements in the tensile behavior of unfilled elastomers.