Conductive thermoplastic polyurethane composites with tunable piezoresistivity by modulating the filler dimensionality for flexible strain sensors

Conductive elastomer composites based strain sensors have attracted increasing attention recently. In this paper, flexible composites were prepared by incorporating thermoplastic polyurethane (TPU) with zero-dimensional carbon black (CB) and one-dimensional carbon nanotubes (CNTs), respectively. CNTs/TPU showed a lower percolation threshold (0.28 wt.%) and wider sensing range (0-ca.135% strain), compared with CB/TPU (1.00 wt.% and 0-ca. 90% strain). CB/TPU composites exhibited a higher sensitivity with a GF of 10.8 under 20% strain, while CNTs/TPU showed a lower GF of 6.8. In cyclic loading-unloading test, both the two composites showed non-monotonic 'shoulder peak' behaviors. For CB/TPU, the 'first peak' was higher than the 'second peak'; interestingly, CNTs/TPU presented a negative strain effect. The discrepancy was mainly ascribed to the difference of filler dimensionality and the evolution of the conductive network.