3D printed high-performance flexible strain sensors based on carbon nanotube and graphene nanoplatelet filled polymer composites

In this study, high-performance flexible strain sensors based on carbon nanotube (CNT) and graphene nanoplatelet (GNP) filled thermoplastic polyurethane (TPU) composites were fabricated via Fused Filament Fabrication (FFF) 3D printing. The introduction of GNPs generated a more complete conductive network of the composites due to the improved nanofiller dispersion. Due to the synergy of CNTs and GNPs, the printed CNT/GNP(3:1)/TPU sensor shows higher sensitivity (GF = 136327.4 at 250% strain), larger detectable range (0-250% strain), and better stability (3000 cycles) compared with the CNT/TPU and GNP/TPU sensors with a nanofiller content of 2 wt%. Furthermore, the printed sensors can accurately detect strains at different frequencies (0.01-1 Hz). A modelling study based on tunneling theory was conducted to analysis the strain sensing mechanism, and the theoretical results agreed well with the experimental data. The capability of the sensors in monitoring physiological activities and speech recognition has also been demonstrated.