Design and characterization of carbon fiber-reinforced PEEK/PEI blends for Fused Filament Fabrication additive manufacturing

We formulated high temperature-resistant thermoplastic composite materials featuring high thermal and mechanical properties for the Fused Filament Fabrication (FFF) additive manufacturing process. The composite materials were blends of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) with weight ratios of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 and 40/60 and all mixed using an extrusion process with 30 wt% chopped carbon fibers (CFs). Differential Scanning Calorimetry measurements on the blends showed a significant increase of the single glass transition temperature, Tg, (up to 37 °C for PEEK/PEI 40/60 formulation), when compared to the neat PEEK, indicating a good miscibility of PEEK and PEI. Microscopy observations using Scanning Electron Microscopy and X-ray microtomography revealed a good dispersion of CFs in the PEEK/PEI blend matrix and also the presence of some voids. Tensile mechanical testing results showed that the highest value of the Young’s Modulus (13 GPa), among all the formulations, is obtained for the composition of reinforced PEEK/PEI (80/20) which also exhibited the lowest degree of porosity (2.90%), and high printability in the FFF process (i.e., high visual quality of the printed parts with no major printing issues). The materials developed here will help move towards manufacturing of functional prototypes made of high-performance composites (e.g., high mechanical properties and high service temperature) using FFF additive manufacturing process for various aerospace applications.