Isothermal annealing optimization for enhanced mechanical performance of FFF-printed PEKK gyroid structures

Purpose This study aims to establish a systematic isothermal annealing post-treatment to mitigate residual stress and poor interlayer adhesion inherent in fused filament fabrication (FFF) of polyetherketoneketone (PEKK), thereby enhancing the mechanical performance of printed components. The optimized protocol is further extended to gyroid triply periodic minimal surface (TPMS) structures to evaluate its broader applicability. Design/methodology/approach Thermal transitions and stability were characterized via differential scanning calorimetry and thermogravimetric analysis, revealing a glass transition temperature of ∼218 °C and stability up to 542 °C. X-ray diffraction and molecular dynamics simulations confirmed predominantly amorphous behavior. Annealing was conducted at 180, 200, 220, 240 and 260 °C for 6 h under constrained conditions followed by furnace cooling, with flexural testing used for the optimization. Failure mechanisms were examined via digital microscopy and scanning electron microscopy. The optimized protocol was validated on cylindrical gyroid structures under compression. Findings Annealing at 240°C increased flexural modulus and strength by 58.7 % and 72.7 %, respectively, shifting failure from delamination to bulk fracture. For gyroid structures, compressive modulus and yield strength improved by 16.7% and 23.2%. Enhancements stemmed from stress relaxation and improved interlayer bonding rather than crystallinity changes. Originality/value This work combines thermal analysis, molecular simulation and failure characterization to explain why annealing improves the performance of amorphous FFF-printed PEKK and provides a practical route for post-processing optimization of complex PEKK structures.