Perfluoroalkoxy alkane (PFA) is a promising candidate for onbaord high-voltage cable insulation due to its superior dielectric properties, chemical resistance, and high thermal stability. Understanding the thermal aging behavior of PFA is essential for ensuring the long-term reliability of insulation materials in hybrid-electric aircraft, where high thermal fluctuations are common. This study investigates the chemical, structural, mechanical, and dielectric properties of PFA aged at 280 °C for up to 1000 h, simulating real-world aerospace operational environments. Results show that PFA undergoes chain scission and chemicrystallization in the early aging stages (0-480 h), leading to an increase in crystallinity. However, at longer aging times e.g. (>480 h), oxidative degradation becomes dominant, resulting in chemical and structural changes correlated with microstructural damage, including crack formation, tie-chain loss, and lamellar disruption. Dynamic mechanical analysis and tensile results show a significant decrease in molecular rigidity with a reduction in glass transition temperature (T_g), indicating a loss of material stiffness and a reduction in tensile strength (42.16%) and elongation (30.2%) after long term exposure (1000 h). Dielectric characterization demonstrates monotonic increase in dielectric constant (from 1.90 to 2.15), dissipation factor, and AC conductivity, attributed to the formation of polar oxidation products and defect-assisted interfacial polarization. The dielectric strength also decreases from 95.2 kV/mm to 87.1 kV/mm after 1000 h of aging. Molecular dynamics simulations (MDS) are also performed to study the temperature effect on PFA, revealing that at high temperatures, the PFA molecular structure is increasingly destroyed by thermal chain scission. These findings provide valuable insight into the degradation mechanisms governing PFA performance and contribute to evaluating its reliability as an insulation material for high-voltage cable systems in hybrid-electric aircraft. ... Read more

Polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), and polyimide (PI) are widely used in aerospace due to their excellent properties. Understanding their aging behavior is essential for long-term performance in extreme environments. This study examines the effects of thermal oxidative aging (at 250°C over varying periods) under humid conditions on their chemical, structural, thermal, mechanical, and dielectric properties. In PEEK, aging led to solidification and crosslinking phenomenon which resulted in increased tensile strength and storage modulus, while elongation at break and tan δ decreased. Dielectric permittivity, polarization charge density, and leakage current also declined with aging, while AC breakdown strength increased by 1.6% in PEEK. PTFE exhibited surface oxidation, thermal degradation, and a decrease in storage modulus, with an increase in loss tangent. Breakdown strength slightly decreased, while dielectric loss and leakage current increased over aging time. PI underwent severe mechanical degradation, with tensile strength reduced by 54% and elongation by 16%, along with oxidation-induced discoloration. Low-mass polar molecules generated in PI during thermal degradation which contributed to the deterioration of its dielectric properties, lead to increased permittivity, polarization, leakage current, and a lower breakdown strength observed after aging. These findings provide insights into degradation mechanisms, aiding aerospace material selection for extreme environments. ... Read more