Effects of 3D printing parameters on the flexural properties of semi-crystalline PEKK

Fused filament fabrication (FFF), a leading additive manufacturing (AM) methodology has revolutionised the production of 3D objects. FFF enables the manufacture of complex geometries not achievable with traditional manufacturing methods. This study investigates the use of the high-performance polymer, polyetherketoneketone (PEKK) for advanced AM applications in the growing field of in-space manufacturing (ISM), where lightweight recyclable metal alternatives can greatly reduce launch payloads. Utilising a response surface methodology, this research examines the effects of print speed, layer thickness, nozzle temperature, and build platform temperature on PEKK's mechanical, physical, and thermal properties. Optimum print conditions for maximising the flexural modulus were identified as 30 mm/s print speed, 0.1 mm layer thickness, 380°C nozzle temperature, and 140°C build platform temperature. These parameters improve the material's crystallinity by extending its residence time in the printer's heated chamber. This prolonged exposure facilitates better molecular alignment and reduces thermal gradients, leading to a 30 % enhancement in crystallinity compared to conditions with higher print speeds and greater layer thicknesses. Scanning Electron Microscopy (SEM) and micro-computed tomography(µCT) analyses revealed that layer thickness significantly influences void formation, with thinner layers yielding superior interlayer bonding and reduced void volume. Differential Scanning Calorimetry (DSC) confirmed that increased crystallisation had a direct impact on flexural modulus, increasing it to 3682 MPa, approaching 80 % of PEKKs injection moulding performance. This study highlights the complex relationships between the FFF parameters and PEKK's mechanical properties, highlighting its potential for industrial and ISM applications.