Improvement of tensile and flexural properties of 3D printed PEEK through the increase of interfacial adhesion

Abstract

Polyetheretherketone (PEEK) is the leading high-performance biocompatible thermoplastic for the replacement of metals in orthopaedic applications. PEEK processing using material extrusion (ME) Additive Manufacturing (AM) techniques such as Fused Filament Fabrication (FFF) highlight its potential for the manufacture of patient-specific load-bearing implantable medical devices. As a high temperature semi-crystalline polymer, the mechanical properties of PEEK 3D printed samples are significantly influenced by printing parameters, particularly the crystallinity and interfacial adhesion of 3D printed parts. Given these challenges, the printing parameters of nozzle temperature, zone heater temperature, layer height and extruder multiplier were selected and studied for their effects in the interfacial adhesion and thus consequent mechanical performance of PEEK 3D prints. Design of Experiment (DoE) studies were conducted where the Taguchi and ANOVA analysis were used to determine the optimal parameter combinations and respective contributions. Additionally, different infill configurations were used with the optimal parameters to lower the samples' void volume and increase interface bonding. Reductions of up to 65 % in void volume were obtained with an interlayer translation of the infill lines and the tested configurations yielded improvements in both the tensile and flexural properties of 3D printed PEEK. Furthermore, high-temperature annealing treatments produced further increases in the strength, stiffness and crystallinity of PEEK samples. With this, significant improvements in both the void volume and the tensile and flexural properties of PEEK prints were achieved in support of the use of 3D printed PEEK in the manufacture of custom-made and high performance implantable medical devices.