Morphological, Thermal, and Mechanical Analysis of 3D Printed Polyetherketoneketone (PEKK) and PEKK‐Hydroxyapatite Composites: Establishing the Reference Enthalpy of Fusion for Crystalline PEKK 7003

ABSTRACT The enthalpy of fusion (ΔH f ) is a critical parameter for determining the degree of crystallinity in semi‐crystalline polymers such as polyetherketoneketone (PEKK). Despite its increasing application in high‐performance and biomedical fields, the widely accepted theoretical ΔH f value of 130 J/g for 100% crystalline PEKK is based on assumptions drawn from related polymers like PEEK. Furthermore, this value may not accurately reflect the behavior of PEKK composite materials. Hydroxyapatite (HA) fillers are increasingly being used in biomedical applications to enhance the bioactivity of normally bioinert materials. However, the presence of HA may influence the crystallization kinetics of the polymer. In this study, the standard ΔH f 100% value was re‐evaluated by implementing differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) measurements on 3D printed PEKK samples subjected to controlled thermal treatments, to maximize the crystalline fraction. The findings suggest a refined theoretical value of 155.24 ± 5.39 J/g for the ΔH f 100% for the PEKK 7003 matrix and offer an indication of how this value transfers to PEKK‐HA composites. This work offers a more accurate basis for the thermal and morphological characterization of PEKK, with implications for both structural and biomedical contexts.