Comparative study of long-term thermo-oxidative aging in composites based on different high-temperature resins

This study presents a comparative investigation of the long-term thermo-oxidative aging of carbon fiber-reinforced composites based on five high-temperature resins: polyimide, phthalonitrile, bismaleimide, phenolic triazine, and organosilicon. Composites were aged in air at 300 and 350°C for up to 500 h under identical conditions. The key finding is that polyimide-based composites exhibit superior stability, with negligible degradation at 300°C, while other resins showed significantly higher degradation rates under the same conditions. Various factors can influence the results of aging. Crucially, no direct correlation was found between the resin’s glass transition temperature and the composite aging rate. Furthermore, a normalization procedure was developed to account for the influence of sample geometry on degradation metrics. The thermo-oxidative degradation kinetics were analyzed using thermogravimetric analysis (TGA) and the advanced integral isoconversional method. A novel applicability criterion (parameter D) for this kinetic approach was introduced and validated. Kinetic predictions of thermo-oxidative aging have been carried out. Although TGA-based kinetic predictions provided approximate estimates, they exhibited limited accuracy for long-term composite aging. This discrepancy is attributed to fundamental differences in reaction zone geometry and diffusion conditions between powdered TGA samples and bulk composite specimens. The work concludes that while TGA-derived kinetics are valuable for preliminary material screening, their predictive power for real composite performance is constrained by these structural factors.