Nanofiller effects on thermo-oxidative durability and mechanical reliability of fiber-reinforced polymer composites

Thermo-oxidative degradation in fiber-reinforced polymer composites is governed by the coupled interaction of oxidation kinetics, oxygen transport, and microstructural deterioration, which collectively influence long-term mechanical reliability. This study investigates degradation–structure–property relationships in neat epoxy and nanofiller-modified composites containing montmorillonite (MMT), carbon nanotubes (CNTs), and layered double hydroxides (LDHs). Conversion-dependent activation-energy (Ea) values were determined using thermogravimetric isoconversional analysis and correlated with oxidation conversion (α), oxygen transport behavior, and mechanical-property retention during accelerated aging. CNT incorporation increased Ea by approximately 19 kJ mol −1 relative to neat epoxy, reduced the effective oxygen-diffusion coefficient by nearly 20%, and improved strength retention by approximately 41% at α = 0.6, indicating enhanced resistance to oxidation-induced degradation. In contrast, LDH-modified systems exhibited lower activation energies and accelerated mechanical deterioration. Diffusion–reaction analysis revealed increasingly diffusion-limited oxidation behavior at advanced aging stages, producing oxidation gradients and localized mechanical heterogeneity consistent with SEM observations. The oxidation-conversion range α = 0.1–0.4 was identified as the critical degradation regime. Among the investigated systems, CNT-modified composites exhibited the most favorable thermo-oxidative durability. The proposed kinetic–mechanical framework provides practical guidance for durability assessment and material selection of fiber-reinforced composites operating in elevated-temperature oxidative environments.