Control of Crystallinity in 3D printed PEEK: Post-deposition Solvent and Thermal Annealing

Tough, semi-crystalline polymers such as poly(ether ether ketone) (PEEK) have recently gained popularity as Material Extrusion (ME) 3D printing feedstocks. However, limited control of crystallinity and complex thermal histories of the deposition process leads to significant anisotropy when printed using fused filament fabrication (FFF). This presentation will describe various methods to control the crystallinity, crystal structure, and spatial distribution of the polymer crystal structures, which in turn dramatically impacts the mechanical properties. Bespoke materials formulation and post-deposition thermal annealing provides pathways to control the extent of crystallinity and its spatial distribution among layers, which is provided by novel  synchrotron wide angle x-ray scattering imaging.  Similarly, solvent annealing in solvent that is a solid at room temperature (4-chlorphenol) or a solvent that is a liquid at room temperature (acetone) are examined as potential protocols to tune the crystalline structure of the 3D printed PEEK.  Our results show that the PEEK crystallinity, crystal morphology, and spatial distribution varies with annealing mechanism, offering novel methods to tune polymer morphology and properties of additively manufactured polymer parts.