On the resistance of PEKK to degradation during multiple recycling cycles for additive manufacturing

• PEKK shows <1% mass loss below 450°C after 5 h, confirming high thermal stability during repeated MEX processing. • Tensile and flexural strengths remain stable after three recycling cycles, indicating preserved mechanical integrity. • Cyclic DSC demonstrates unchanged melting and crystallization behavior under repeated thermal exposure. • FTIR, XRF, and SEM analyses reveal minimal chemical modification and limited contamination (<0.5 wt%). • PEKK exhibits superior recyclability compared with conventional AM polymers, supporting circular high-performance manufacturing. The recyclability of high-performance poly(ether ketone ketone) (PEKK) is critical for sustainable additive manufacturing and future in-space resource utilization. This study systematically evaluates the thermal, mechanical, and chemical stability of PEKK subjected to multiple recycling loops to elucidate potential degradation mechanisms. Thermogravimetric analysis revealed negligible (<1%) mass loss after 5 h of isothermal exposure below 450°C, confirming the polymer’s excellent thermal resistance under extrusion and printing conditions. Cyclic differential scanning calorimetry (DSC) demonstrated stable melting and cold-crystallization behavior across six thermal cycles, indicating preserved crystallization kinetics. Tensile testing showed that the amorphous strength remained within 83–91 MPa across all cycles, while annealed samples maintained strengths of 102–116 MPa. Flexural strength similarly remained consistent, ranging from 112–127 MPa (amorphous) and 147–160 MPa (annealed), and dynamic mechanical analysis (DMA) results indicated minimal changes in viscoelastic properties. Together, these mechanical and thermomechanical analyses confirm that PEKK retains its structural integrity after three complete recycling sequences involving shredding, pulverization, extrusion, and reprinting. Fourier transform infrared spectroscopy detected no new carbonyl or hydroxyl bands, excluding oxidative chain scission, while X-ray fluorescence (XRF) revealed only trace (<0.5 wt%) metallic contamination. Scanning electron microscopy (SEM) of fracture surfaces further confirmed well-fused interlayer morphology and minimal porosity evolution. Collectively, these results demonstrate that PEKK maintains its molecular and microstructural integrity during repeated thermal–mechanical cycles, highlighting its exceptional thermal-oxidative stability and its suitability for circular, high-performance, and extended-lifetime polymer applications.