Slow and fast crystallising poly aryl ether ketones (PAEKs) in 3D printing: Crystallisation kinetics, morphology, and mechanical properties

Poly aryl ether ketone (PAEK) polymers are gaining interest in 3D printing for their good mechanical properties and high service temperatures. The aim of this study was to compare the crystallisation kinetics, morphology, and mechanical properties of two different PAEK polymers used in fused filament fabrication (FFF), i.e. the fast crystallising PEEK151 (poly ether ether ketone) grade originally designed for injection moulding and the slow crystallising AM 200 grade tailored specifically for FFF. The crystallisation kinetics of both grades were examined across a wide temperature range. A method to select annealing temperatures and annealing times based on the intrinsic crystallisation behaviour of each polymer was proposed. The dual-Avrami model highlighted a different crystallite growth for AM 200 in comparison with PEEK151 with a higher rate of secondary crystallisation. Lamellar thicknesses were measured by SAXS and calculated via the Thomson-Gibbs equation. The lamellar thicknesses of primary and secondary crystallisation for AM 200 showed a stronger temperature dependence with steeper slopes when increasing the isothermal temperature. The benefit of using a slow crystallising PAEK polymer over the conventional fast crystallising grades is evidenced by the improvement in Z strength which enhances the overall isotropy of printed parts.