Direct 4D printing: pellet extrusion of shape memory polymer composites with large-scale additive manufacturing machine

Purpose Shape memory polymers (SMPs) can temporarily store a shape and return to their permanent/original form upon the application of a stimulus. Despite their potential, SMPs large-scale implementation is still hindered due to their limited stress recovery responses. This study aims to investigate the feasibility of producing SMP composites (SMPCs) with enhanced mechanical and recovery properties using additive manufacturing, also known as 4D printing, for large-scale manufacturing. The long-term objective is to 4D print functional robotic components, such as drone wings capable of shapeshifting for improved manoeuvrability in flight. Design/methodology/approach A large-scale extrusion-based 3D printer was adapted with a pellet extruder to fabricate SMPC samples. The polymer blend used consisted of SMP polyurethane-based pellets and polylactic acid (PLA) pellets containing 15% carbon fibre (CF). Compositions of 0%, 10% and 20% CF PLA on the SMP were evaluated for shape recovery, fixity ratio and shape recovery flexural stress. Findings Results indicated that the highest CF content tested – 20% CF PLA on the SMP – improved shape recovery under flexural stresses by over 400% compared to unreinforced polymer. However, this enhancement came at a cost: shape recovery ratio decreased by up to 7%, and shape fixity decreased by 22%. These findings indicate that while the incorporation of CF improves certain properties, it may also compromise the material’s ability to fully recover its original shape. Originality/value SMPCs are produced using a large-scale extrusion-based 3D printing platform, marking a crucial step in scaling 4D printing technologies and the manufacturing of shape-shifting materials for engineering applications.