Effects of fused filament fabrication process parameters on tensile properties of polyether ketone ketone (PEKK)

Fused filament fabrication (FFF) is an additive manufacturing (AM) technology which is rapidly progressing from production of prototypes to manufacture of customized end use parts for the automotive, biomedical, and aerospace industries. The properties of manufactured parts have been proven to be dependent on not only the material's inherent properties but importantly the FFF process parameters. Commodity thermoplastics such as acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) have been on the forefront of FFF research since its development. However, as FFF technology progresses from rapid prototyping to rapid manufacturing, understanding the behaviour of high-performance engineering thermoplastics in this process is imperative. While previous studies have investigated the effects of FFF process parameters on polyether ether ketone (PEEK) and polyetherimide (PEI), more limited research has been performed on polyether ketone ketone (PEKK) despite its widespread applications in the biomedical and aerospace industries. This study investigated the effects of process parameters including build orientation, infill pattern, number of contours and raster angle on the tensile properties of PEKK. Tensile test results showed significant variations in Young's modulus and elongation at break. Statistical analysis was performed which determined the optimum process parameters to maximize tensile properties and revealed that build orientation was the most significant parameter, followed by number of contours. Fractography showed differences in failure mode and ductility among the sample groups. Analysis using differential scanning calorimetry (DSC) showed that the difference in percentage crystallinity among sample groups was not significant and thus the varied tensile properties was improbable to be due to differences in crystallinity developed within the specimens. Further analysis revealed that a variation in FFF process parameters can cause differences in percentage, size and location of porosity which in turn affects mechanical properties.