Effect of aging on the properties of PEEK fabricated via fused filament fabrication

Polyether ether ketone (PEEK) is a high-performance thermoplastic widely used in aerospace, biomedical, automotive, and nuclear sectors owing to its excellent mechanical, thermal, and chemical stability. Fused filament fabrication (FFF) has recently emerged as an accessible additive manufacturing route for PEEK, enabling the production of customized components with complex geometries. However, the long-term aging behavior of FFF-printed PEEK remains poorly understood. Environmental stressors such as UV radiation, humidity, and temperature can induce chain scission, oxidation, and crystallinity variations, ultimately affecting structural integrity and durability. Moreover, intrinsic microstructural features of FFF, including interlayer porosity and filament orientation, may amplify these degradation phenomena compared to bulk PEEK. This study investigates the effects of controlled environmental aging — UV exposure, hygrothermal conditions, and combined UV + hygrothermal treatments — on the mechanical, chemical, and tribological properties of FFF-printed PEEK. Mechanical (tensile, hardness, and wear), chemical (FTIR, EDXS), and morphological (SEM) analyses were employed. UV aging induced marked surface photo-oxidation and cracking, while unexpectedly enhancing tensile strength and ductility, indicating damage confined to the outer surface. Hygrothermal aging caused no significant oxidation but increased crystallinity and stiffness, with limited effects on tensile properties and a moderate reduction in wear resistance. The combined UV+HT treatment produced the most severe surface oxidation and erosion together with the highest strength and ductility, but the poorest tribological performance. Overall, the results demonstrate a decoupling between surface degradation and bulk mechanical behavior, revealing new pathways for tuning performance and guiding protection strategies for FFF-printed PEEK.