Multi-Scale Polyetheretherketone Investigations into a Novel Additive Manufacturing Process Based on Material Extrusion

Abstract

Material extrusion (MEX) is a popular additive manufacturing (AM) technique based on selective material deposition dispensed through a nozzle forming successive layers. The technique is widely used to produce polymeric parts and more recently has been developed for use with advanced polymeric materials. In this context, the polyaryletherketone (PAEK) family arouse great interest due to its high performance, especially in high temperature applications. Polyetheretherketone (PEEK) belongs to the PAEK family and has great potential for MEX application. This research work was developed using PEEK 450G™ and was joint funded by the University of Exeter and BOND 3D®, a company focused on cutting-edge additive manufacturing technology, which uses this material in an innovative MEX system. The research work investigated crystallisation kinetics of PEEK in isothermal and non-isothermal conditions and within the BOND 3D® additive manufacturing process, which exposes the material to complex thermal profiles. Also, the influence of different morphologies and degrees of crystallinity on the MEX process were investigated. Typical PEEK behaviours, such as the multiple melting peaks were analysed in isothermal, non-isothermal, and specific process configurations, thanks to a process simulation approach, based on the Fast-Scanning Calorimetry (FSC) technique. The possibility of simulating the processes also allowed the evaluation of key parameters, such as build chamber temperature or the layer time in the crystallisation process. The remelting promoted by the deposition of filaments on previously produced layers was also measured along with the crystallisation evolution at specific critical filament regions, helping to explain layer adhesion mechanisms. The results showed significant variations in crystallisation as a function of the thermal cycles. Considering that the thermal cycles to which the material is submitted can be adjusted, it was possible to draw a correlation between the process parameters and the nature of the crystalline phase at a micro-level. Finally, the results were supported by mechanical tests as well as morphology evaluation.