Quantitative Kinetic Analysis of Hydraulic Aging in EPDM Rubber: Evolution of Functional Properties

The long-term effects of water immersion on the physicochemical and functional properties of ethylene-propylene-diene monomer (EPDM) elastomer, widely used as insulation in medium-voltage electrical cables, were investigated over a period of 140 days at room temperature. A multi-scale experimental approach combining complementary characterization techniques was employed to establish quantitative correlations between moisture-induced physicochemical changes and the resulting evolution of functional performance. Water uptake, governed by Fickian diffusion kinetics, remained limited to 0.30 wt%. At the surface, progressive roughening was observed alongside the formation of microcavities and microcracks. Leaching of mineral fillers and an increase in surface polarity were found to enhance wettability. These combined physicochemical alterations translated into measurable degradation of functional properties, with two distinct kinetic regimes identified. Shore hardness, volume resistivity, and dielectric strength underwent rapid deterioration within the first few days of immersion, whereas tensile strength, elongation at break, dielectric permittivity, and dielectric loss factor evolved more gradually over timescales of several tens of days. Temporal profiles for each property were fitted to appropriate models, and characteristic degradation timescales were estimated. These findings provide a structured, physically grounded picture of EPDM degradation under water exposure and offer quantitative data to support the development of service-life prediction models for cable insulation systems.