Fabrication of continuous carbon fibre-reinforced polyetherimide through fused filament fabrication

The transition of additive manufacturing (AM) from a technique to rapidly fabricate prototypes to one capable of producing final components is driving the demand for robust AM methodologies as well as materials with superior processability and mechanical performance tailored for AM. Polymer matrix composites are used for light-weighting in many industry sectors including automotive and aerospace and are of considerable interest as material feedstocks for AM. Although fused filament fabrication (FFF) based AM is well known to be suitable to process short (chopped or milled) fibre polymer matrix composites to this point much less progress has been made on the FFF of continuous fibre reinforced high-performance polymers. In this research study, a novel FFF heating block was developed and employed to fabricate polyetherimide (PEI) composite components employing continuous carbon fibres (CF) as the reinforcement. The effect of CF sizing agent was explored as a mechanism to improve fibre/matrix compatibility, hence processability and part performance. The successful fabrication of specimens is demonstrated using the technique and build morphology analysed. In addition, the mechanical behaviour of single CF reinforced PEI filaments deposited by FFF is examined in tension and compared and related to that of the plain CF and unreinforced single filaments. It was found that the tensile strength of the reinforced single filaments was nearly triple that of the unreinforced filaments but notably lower than that of the CF, which shows that characteristics such as the fibre/ matrix interface and distribution of fibres within the filaments possibly need to further be improved.