4D printing of multi-stimuli responsive thermoplastic vulcanizate composites via pellet-based material extrusion

Thermoplastic vulcanizates (TPVs) have been developed as sustainable alternatives to nonrecyclable thermoset elastomers, combining the elastic performance of rubbers with the recyclability and processability of thermoplastics. In this study, a pellet-based material extrusion approach was used as a reliable printing method to process multi-stimuli responsive PLA-EVA-Fe TPV composites. Six different formulations were prepared to investigate the influence of EVA, dynamic vulcanisation (DV), and iron loading. Torque-time analysis during melt blending revealed a significant increase in torque upon addition of the crosslinking agent, confirming increased melt viscosity and successful DV. DMTA showed that composites with higher PLA-Fe content exhibited increased storage modulus, while tensile testing demonstrated improved elongation at break in EVA-rich and crosslinked composites. Furthermore, the study demonstrates the feasibility of 4D printing with TPV composites. The printed structures exhibited multi-stimuli shape memory behaviour under direct thermal actuation as well as indirect photothermal (NIR light) and magnetothermal (alternating magnetic field) triggering modalities. Shape memory tests indicated excellent shape fixation above 95% for all composites, along with efficient and rapid shape recovery. All composites under thermal stimulation recovered under 7 s. In addition, the conceptual feasibility of these materials for remote NIR-triggered deployable space structures is demonstrated.