Optimization of fused filament fabrication process parameters to improve the compressive properties of PEEK and PEKK biomaterials.

Fused filament fabrication (FFF) is increasingly being adopted to create polymeric orthopedic devices. FFF process parameters determine the mechanical performance of final printed parts; hence, optimizing for appropriate levels of strength is critical for load-bearing applications. We utilized a Taguchi L-9 orthogonal array to investigate the impact of nozzle temperature (TN), chamber temperature (TCh), layer height (LH), and print speed (PS) on the compressive properties of cylindrical polyether-ether-ketone (PEEK) and polyether-ketone-ketone (PEKK). The printed specimens were examined using optical microscopy, scanning electron microscopy, and differential scanning calorimetry to understand the effect of the printing parameters on their macrostructures. The optimized parameter combination for the elastic modulus (E) of PEEK and PEKK was 390 °C TN, (190 °C-PEEK, 110 °C-PEKK) TCh, 0.1 mm LH, and 1000 mm/min PS, with LH and PS having the most impact on their stiffness. For the offset yield strength (YS), the optimized parameters were (410 °C-PEEK, 400 °C-PEKK) TN, (210 °C-PEEK, 150 °C-PEKK) TCh, 0.1 mm LH, and (1000 mm/min-PEEK, 1500 mm/min-PEKK) PS, with TN, TCh, and LH significantly impacting both materials. Elevated thermal conditions enhanced the strength of both materials; however, in PEEK, this was achieved by slowing down its crystallization kinetics, while in PEKK, it increased tendency for crystallization. The print conditions significantly affected the crystallinity of PEKK but not PEEK. Additionally, the highest E of PEEK and PEKK were 113 % and 106 % of the expected value of unreinforced PEEK (3.3 GPa), whereas the highest YS were 132 % and 120 % higher (94 MPa), respectively, indicating PEKK's potential for spinal cage applications.