A novel method of fabricating designable polylactic acid (PLA)/thermoplastic polyurethane (TPU) composite filaments and structures by material extrusion additive manufacturing

Multi-material 3D printing enables the creation of complex parts with tailored mechanical properties, which expands the potential of material extrusion additive manufacturing (MEAM). A promising approach to realise multi-material printing is to manufacture a composite filament, integrating multiple materials into a filament that can be further processed on a single extruder machine. However, making such composite filaments typically requires specialised equipment, which in turn limits its application in multi-material printing and increases costs. This study presents a novel and cost-effective approach for fabricating composite structures with enhanced mechanical properties. In this method, a commercially available 3D printer is employed to manufacture polylactic acid (PLA) and thermoplastic polyurethane (TPU) into core-shell composite filaments. The fabricated core-shell filaments are further used as feedstocks in the re-extrusion process to make composite specimens. In addition, the effects of multiple process parameters and geometrical design strategies on re-extruded materials are comprehensively evaluated by microscopy analysis, nanoindentation and tensile testing. The design with the best mechanical properties has a volume fraction of the PLA core (V_f) of 36 %, which results in a 63 % higher in toughness than the neat TPU and 27 times higher than neat PLA. Overall, the approach offers a promising way for rapid prototyping and testing of various material configurations.