Development of discontinuous fibre reinforced thermoplastic feedstocks for high performance 3D printing

Fused filament fabrication (FFF) is a 3D printing technique which allows layer-by-layer buildup of a part by the deposition of thermoplastic material through a nozzle. The technique allows for complex shapes to be made with a degree of design freedom unachievable with traditional manufacturing methods. However, the mechanical properties of the thermoplastic materials typically used are low compared to traditional high performance engineering materials. In this work, the development of improved 3D printing feedstocks for FFF is shown, with discontinuous (3mm) carbon fibres embedded in a thermoplastic matrix to reinforce the material. One unique aspect of the proposed approach is that that fibre breakage which limits existing fibre reinforced filament mixing and extrusion techniques is prevented during filament manufacture, such that the fibres are above the critical fibre length for maximum strength, without compromising processing flexibility. One of the critical aspects of this work is selection of the thermoplastic matrix material, as it significantly impacts both processing and performance. This paper therefore focuses on a down-selection process for candidate polymers. First, a pre-selection was made to identify suitable matrices for filament fabrication and printing based on an array of different material, mechanical, and thermodynamic properties. Four matrix materials (ABS, PLA, Nylon, PETG) were then used to manufacture aligned discontinuous fibre thermoplastic (ADFRTP) preforms with a Vf of 12% using an in-house developed continuous consolidation module. Tensile stiffnesses and strengths of ADFRTPs up to 23 GPa and 300 MPa respectively were recorded. This investigation shows that discontinuous fibre filament has the potential to compete with continuous fibre filaments. Future work consists of forming the ADFRTP tapes into a uniform filament and investigations into the interfacial and flow properties of the ADFRTPs.