Steam‐Aging Durability of DES ‐Modified Fiber‐Reinforced EPDM Composites for High‐Temperature Pipeline Liners

ABSTRACT

Trenchless rehabilitation of urban district heating pipelines places stringent requirements on the hygrothermal durability of liner materials. In this work, ethylene propylene diene monomer (EPDM) was used to fabricate fiber‐reinforced liner pipes containing a small amount of deep eutectic solvent (DES), and accelerated aging tests were conducted in saturated steam at 180°C and 200°C. Thermogravimetric analysis (TGA), oxidation induction time (OIT), crosslink density, tensile testing, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used to evaluate the thermal response, residual oxidative stability, network structure, representative tensile response, spectral evolution, and visible morphology of the composite liners. The results show that the incorporation of DES increased the initial crosslink density and tensile response of the EPDM system. In the unaged state, the crosslink density increased from 6.64 × 10 ⁻⁵ to 8.22 × 10 ⁻⁵  mol/cm ³ , while the tensile strength and elongation at break increased from 9.70 MPa and 254.08% to 12.57 MPa and 292.28%, respectively. After aging at 180°C for 10 days, the DES‐containing sample retained a higher residual absolute tensile response and network compactness. Under the more severe 200°C condition, this advantage became less pronounced. OIT, FTIR, and SEM results are interpreted as supportive evidence for condition‐dependent structural evolution. These findings suggest that DES modification can improve the steam‐aging durability of fiber‐reinforced EPDM composites within a defined temperature window, while its benefit is attenuated under severe saturated‐steam aging.