Temperature-dependent swelling behavior of EPDM vulcanizates with varying ethylene content based on hansen solubility parameter approach

Abstract

The swelling behavior of two ethylene-propylene-diene monomer (EPDM) vulcanizates with different ethylene contents, denoted as EPDM44 and EPDM52, was systematically investigated in cyclohexane, xylene, and cyclohexanone at different temperatures using the equilibrium swelling method. The effects of solvent type, ethylene content, and swelling temperature on the maximum equilibrium swelling ratio (q m ) were quantitatively evaluated. For both EPDM vulcanizates, the q m values followed the order cyclohexane > xylene > cyclohexanone, reflecting the stronger affinity of nonpolar solvents toward the nonpolar EPDM network. EPDM52 exhibited slightly lower swelling ratios than EPDM44, which was attributed to its higher ethylene content, enhanced chain regularity, and more compact network structure. With increasing temperature, q m decreased slightly in cyclohexane and xylene but increased in cyclohexanone, indicating a solvent-dependent competition between thermally activated diffusion and elastic retraction of the crosslinked network. Although the Hansen solubility-distance parameter (Ra) qualitatively described solvent compatibility, it failed to capture temperature-dependent swelling behavior. Therefore, a Hansen-based Flory-Huggins interaction parameter (χ HSP ) was introduced, showing a strong negative correlation with q m . The established fitting model accurately predicted experimental swelling ratios, with R 2 = 0.9925, providing a reliable framework for solvent-resistance evaluation and service-environment screening of EPDM vulcanizates.