Hydrothermal aging of carbon fiber reinforced polyether ether ketone composites: Behavior, mechanism and life prediction

Currently, carbon fiber reinforced polyether ether ketone (CF/PEEK) composites are being used more and more widely. However, their hydrothermal aging behavior and mechanism are still unclear, and their service life assessment is also insufficient. In this study, the hydrothermal aging behavior of CF/PEEK composites was investigated from water absorption and desorption, mechanical property evolution, and the relationship between them for the first time. The hydrothermal aging mechanism was discussed in detail from physical deterioration and chemical deterioration. The adhesion of PEEK on the CF surface was weakened, and the roughness of the CF/PEEK composites surface was enhanced on both μm-scale and nm-scale through hydrothermal aging. The thermo-mechanical property of CF/PEEK composites was reduced and crystallization behavior was changed, demonstrating enhanced mobility and declined ordering of PEEK molecular chains induced by hydrothermal aging. FT-IR and XPS results on the CF/PEEK composites surface suggested that hydrothermal aging led to random chain scission in ether groups and benzene ring opening, and subsequently, aliphatic polyether, carbonyl groups, and carboxyl groups were increased, and ester groups were created simultaneously, thus causing the generation of small molecules with lower molecular weight. Meanwhile, the creation or increase in oxygen-containing functional groups, especially carboxyl groups, whose generation inevitably resulted in chain breakage or opening of aromatic rings, provided a reasonable explanation for the enhancement of surface roughness on the nanoscale through the creation of side arms. Additionally, the service life of CF/PEEK composites in the marine industry was predicted based on the hydrothermal aging mechanism, which was expected to provide beneficial assurance for its practical application. Highlights: Hydrothermal aging of CF/PEEK composites was first investigated. Chain scission in ether groups and aromatic rings opening was first disclosed. Variation in surface roughness was first explored on μm-scale and nm-scale. Roughness enhancement was linked to skeleton fracture by the creation of side arms.