Thermal and rheological transitions of high performance semicrystalline polyaryletherketone (PAEK) polymers in material extrusion (MEX)

Abstract

Mechanical properties in material extrusion (MEX) processes are influenced by the printing conditions and the cooling profile of extruded polymer. During cooling, the polymer transitions from a viscoelastic fluid to a “rubber” like state and ends as a glassy solid. The time taken to transition through each region is unique to individual polymers and it is linked to the melt rheology, thus indirectly affecting the layer to layer bond strength. By combining several thermal and thermomechanical methods, dynamic mechanical analysis (DMA), rotational rheometry (RR), differential scanning calorimetry (DSC) and infrared (IR) thermography, this paper defines the time a semicrystalline polymer takes to pass through each thermal transition region under a specific cooling regime. From the results, Victrex PAEK AM 200 spent 0.1 seconds in complete melt (terminal region), before beginning to solidify (rubbery region), taking a total of 0.95 seconds to reach complete solidification (glassy region). Defining these transition regions allows us to control the printing parameters for optimum interface bond strength, as the time spent in the terminal and rubbery regions governs interlayer diffusion. This is the first study to approach the combined melt rheology and solidification profile of a high-performance polymer in order to understand critical points within the printing process and identify ways of controlling them, providing quantitative values for the onset and endset of solidification of extruded polymer in MEX.