Influence of Thermal Aging on the Crystallinity of EPDM Used in Power Cables Insulation

In this work, ethylene propylene diene monomer (EPDM) used in power cables insulation was exposed to a thermal aging at different temperatures ranging from $80^{\circ}C$ to $140^{\circ}C$. Two complementary characterization techniques were used to track changes in EPDM crystalline structure during thermal aging. Differential scanning calorimetry (DSC) analysis was performed to measure the variation of the melting enthalpy $\Delta H_{m}$. To highlight the modifications induced on the crystalline and amorphous fractions of the EPDM structure, we carried out X-ray diffraction (XRD) measurements. The results of both methods agree in the time and temperature dependence of the aging process. The results show that the crystallinity is improved when aging is carried out at a low temperature. When temperature increases, minor changes in the crystallinity occur at the end of the aging process. At the highest aging temperature, a drop in the crystallinity occurs from the first hours of aging, indicating a degradation of the molecular structure of the polymer.