Polyether ether ketone (PEEK) composites face concurrent ultraviolet (UV) and thermo-oxidative aging in real-world service environments, yet the synergistic effects remain poorly understood. This study systematically decouples the degradation pathways of three PEEK-based materials – neat PEEK (PK), 30 wt% CF-reinforced PEEK (UG), and PTFE/Gr/CF-modified PEEK (VMT) – under isochronal (1500 h) UV and thermo-oxidative aging, establishing a comprehensive structure-property evolution chain.
UV aging causes more severe surface oxidation and performance deterioration than thermo-oxidative aging across all materials. Carbon fibers effectively mitigate UV-induced degradation, enabling UG to achieve the highest compressive strength retention (81.0% after UV). The PTFE/Gr combination in VMT maintains the lowest steady-state friction coefficient (0.428 after UV) through the formation of low-shear, lubricating transfer films on the counterface. This work provides a comparative assessment of UV versus thermo-oxidative aging and offers practical guidance for selecting high-performance PEEK composites for multifactorial service environments such as aerospace bearings and high-temperature seals.
Background
PEEK and its composites are extensively used in demanding applications, including aerospace, automotive, and medical devices, due to their exceptional mechanical strength, thermal stability, and chemical resistance. However, in real-world service environments – particularly outdoor or thermally fluctuating conditions – PEEK components are simultaneously exposed to UV radiation and thermo-oxidative stress. These aging mechanisms trigger chain scission, cross-linking, and oxidation, leading to surface cracking, internal structural degradation, and ultimately compromised mechanical and tribological performance.
Despite extensive research on PEEK aging, critical knowledge gaps remain: (1) a lack of direct, systematic comparisons between UV and thermo-oxidative aging under equivalent exposure durations and cyclic protocols; (2) an unclear understanding of how functional fillers (CF, PTFE, Gr) confer material-dependent aging resistance through filler-matrix interactions; and (3) an absence of a holistic understanding of how aging couples bulk mechanical/thermal properties with tribological response. This study addresses these challenges by decoupling the contributions of UV and thermo-oxidative degradation to overall performance deterioration.
Highlights
Highlight 1: Decouples UV and thermo-oxidative degradation pathways on the tribo-mechanical performance of PEEK composites.
Highlight 2: UV aging causes more severe deterioration in friction, wear, and mechanical properties than thermo-oxidative aging.
Highlight 3: Carbon fiber reinforcement (UG) optimally mitigates strength loss and wear via load-bearing and debris rolling mechanisms.
Highlight 4: PTFE/graphite solid lubricants (VMT) maintain the lowest friction through formation of lubricating transfer films, though graphite oxidation compromises lubricity and leads to the largest relative increase in friction coefficient under UV.
Highlight 5: Raman mapping quantifies aging-induced graphite disorder, directly linking interfacial degradation to impaired solid lubricity and increased wear.