Thermal Aging Behavior of PFA-Insulated Cables for Future Electrified Aircraft: From Material Evolution to Cable-Level Mechanical Response

The thermal reliability of high-voltage aerospace cables is increasingly important for hybrid-electric and all-electric aircraft; however, most thermal aging studies of perfluoroalkoxy alkane (PFA) have focused on isolated specimens and therefore do not establish how material-scale aging translates into the response of a complete cable structure. In this work, a PFA-insulated cable comprising the conductor, primary insulation, and outer jacket was subjected to cyclic thermal aging with a maximum temperature of 280 °C for nominal elapsed durations of up to 1000 h. Each 24 h cycle comprised approximately 1 h of heat-up and 7 h of nominal dwell at 280 °C, followed by natural cooling and recovery. Macroscopic, FTIR, DSC, XRD, TGA, TG–MS, SEM/EDS, contact angle, DMA, tensile, and three-point bending analyses were used to correlate aging of the individual PFA layers with cable-level behavior. The results indicate two dominant aging regimes over the investigated intervals. During the earlier 0–500 h interval, physical annealing and structural ordering predominated, producing increased crystalline organization, morphological densification, restricted molecular mobility, and initial mechanical stiffening. At the later 720–1000 h conditions, degradation-associated structural rearrangement or possible chemi-crystallization became increasingly evident, accompanied by localized morphological defects, partial recovery of molecular mobility, and progressive loss of ductility. The outer jacket exhibited more pronounced aging-related changes in several thermal, morphological, and mechanical responses than the primary insulation. At the cable level, aging was further manifested by axial shrink-back and changes in bending force, secant stiffness, bending work, and apparent structural bending rigidity. The mechanical end-of-life criterion was not reached under the investigated conditions. By linking aging of the individual PFA layers to the dimensional and mechanical response of the assembled cable, this work extends previous material-level PFA aging studies toward cable-scale durability assessment for future electrified aircraft wiring systems.