Mobile amorphous fraction in polyaryletherketones and its influence on interlayer bonding in material extrusion

Abstract

In general, the mechanical properties of parts manufactured by material extrusion (MEX) process depend upon the interlayer bonding strength. In the case of high temperature polymers such as polyaryletherketones (PAEKs), the printing parameters, in particular the temperatures applied within the process, become a critical factor. The printing-structure-property relationship for these semicrystalline high temperature polymers is complex and not fully understood, often relying on statistical analysis to identify the trends between the processing parameters and the mechanical properties, while missing the microstructural interpretation in between. By controlling the temperature settings and the printing speeds, PAEK parts can be printed in an amorphous state or semicrystalline state. In both cases, molecular chain diffusion at the interface is crucial for achieving good mechanical properties. Using temperature profiles directly determined by the printing parameters, the current work investigates the formation of mobile amorphous fraction (MAF) during printing and its correlation with the correspondent Z tensile strengths. MAF is defined as the fraction of amorphous phase with a higher mobility, which is beneficial to chain d iffusion. The conditions required to generate MAF is explored by fast scanning calorimetry (FSC). The MAF-Z strength correlation is aiming to provide a deeper understanding of the complete processing-structure-property relationships of the MEX process for semicrystalline polymers. It may also provide a microstructural explanation on why slow crystallising PAEK grades are desirable in the MEX process. This study is concentrated on PAEKs which have been printed in an amorphous state to avoid the effect of crystallisation kinetics.