Novel backbone modified polyetheretherketone (PEEK) grades for powder bed fusion with enhanced elongation at break

This study presents a new family of backbone modified polyetheretherketone (PEEK) grades in the powder bed fusion (PBF) process, coded as PAEK1 and PAEK2, with the same chemical structure but different molecular weights. By incorporating polyetherbiphenyletherketone (PEDEK) comonomer, the optimal powder bed temperature of the new grades could be reduced to 290 °C, approximately 40 °C lower than that of PEEK. The underlying crystallisation kinetics in the PBF process was investigated by replicating the in-process temperature profiles using a flash differential scanning calorimetry (DSC) machine. This method enabled monitoring of the development of crystallisation during the process and at different deposition thicknesses. The results confirmed that the PAEK2 grade with a higher molecular weight is slower crystallising. A significant part of the crystallisation of PAEK2 was found taking place in the later stage of the printing process, i.e. the free cooling stage. This leads to a better particle coalescence and enhanced elongation, a feature previously difficult to obtain in the PBF process. The PBF PAEK2 tensile bars achieved a significant increase in mechanical performance with an outstanding 13% in elongation, reaching its yielding point. The data supports that PAEK2 is the first high temperature polymer grade in the PBF process to match its bulk mechanical properties while maintaining a high level of crystallinity in the printed parts.