Study of degradation mechanisms of the polymer matrix in carbon fiber composites.

Carbon fiber composite cores are increasingly incorporated in high‑voltage overhead conductors owing to their superior performance in terms of strength to weight ratio, low thermal expansion, and good sag performance compared to the steel‑reinforced counterparts. However, the long‑term reliability of the advanced conductors is critically dependent upon the stability of the polymer matrix that binds and protects the carbon fibers. This study presents an investigation of degradation mechanisms of a polymer matrix within carbon fiber composite cores subjected to thermo‑electrical, mechanical, and environmental stressors typical for high‑voltage power transmission systems. The study investigates the individual and combined impacts of cyclic thermal loading, sustained tensile stress, moisture ingression, and corona-induced oxidative species. These effects activate several degradation mechanisms, such as hydrothermal plasticization, thermo-oxidative aging, and progressive degradation of the fiber-matrix interface. Accelerated aging protocols that simulate conductor operating temperatures, and field-relevant environmental cycles are employed. This will enhance predictive capabilities for service life for relevant loading conditions. Alterations in chemical structure, viscoelastic behavior, and microstructural integrity are quantified through Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results indicate that combined thermal and environmental exposures can expedite matrix embrittlement, depress glass transition temperature, enhance microcracking sites, and degrade interfacial adhesion. Polymer degradation has significant ramifications for conductor-level properties by reducing stiffness, increasing creep susceptibility, and contributing to long-term sag. This study presents a thorough assessment of matrix degradation in carbon fiber composite cores for high-voltage power transmission systems as well as important mechanisms limiting their durability. It is important in the production of advanced resin materials, applications in protecting composites, as well as design methods geared towards advanced high-performance conductors used in overhead systems.