Investigation of the microstructure, mechanical properties and thermal degradation kinetics of EPDM under thermo-stress conditions used for joint sealing of floating prefabricated concrete platform of offshore wind power

The prefabricated concrete platform, a novel floating structure for offshore wind power, utilizes ethylene propylene diene monomer (EPDM) to seal joints and prevent seawater ingress. However, quantitative assessments of thermo-stress aging effect on EPDM degradation—particularly regarding apparent activation energy (Ea)—remain underexplored. In this study, EPDM composites were systematically evaluated under thermo-oxidative aging (70 ℃ and 100 ℃) and thermo-stress aging (20 % static strain at 70 ℃ or 100 ℃). Macroscopic mechanical properties (i.e., Shore hardness, tensile strength and elongation at break), creep behavior, and microscopic characteristics were analyzed using SEM, FTIR, and TGA, while thermal degradation kinetics were quantified via the Kissinger, Ozawa, and Flynn-Wall-Ozawa methods to determine Ea. The results demonstrated that elevated aging temperatures and applied loads significantly degraded EPDM's structural integrity: specimens aged at 100 °C exhibited a 130 %-145 % greater reduction in elongation at break compared to those aged at 70 °C, alongside a 3–28 kJ/mol decline in Ea. Thermo-stress aging induced more severe degradation than thermo-oxidative aging, with additional reductions in elongation at break (0–12 %) and Ea (2–18 kJ/mol). The thermo-stress aged EPDM under 0.5 MPa stress demonstrated accelerated creep deformation, reaching a maximum strain of 0.16 within 1800 s at room temperature. FTIR analysis confirmed molecular chain oxidation (2925 cm⁻¹) and carbonyl group formation (1720 cm⁻¹), directly correlating with mechanical property losses. These findings quantitatively establish that thermal oxygen exposure and applied load synergistically exacerbate molecular chain scission and cross-linking in EPDM, reducing thermal stability by 8 %-18 % as quantified through apparent activation energy analysis. This study advances seepage-resistant joint design for offshore concrete floating wind platforms, demonstrating that integrating thermo-stress aging resistance into EPDM sealants is essential for ensuring durable marine infrastructure.