Graphene/carbon nanotube hybrid networks in TPU composites for shoulder-free and stable strain sensing

Thermoplastic polyurethane (TPU) is attractive for flexible strain sensors, but single carbon-filler systems often suffer from unstable conductive-network evolution and unreliable cyclic signals. Here, graphene (GR), carbon nanotubes (CNTs), and GR/CNT hybrid fillers were incorporated into TPU by solution blending to regulate network stability and shoulder-peak behavior. Among the investigated formulations, GCTP exhibited a tensile strength of 20.64 MPa, an elongation at break of 974.54%, GF values of 1.86, 183.14, and 1975.6, an effective sensing range of ~280%, and a response time of ~330 ms. It also maintained recognizable resistance signals after 5,000 cycles at 60% strain. Notably, GCTP showed smooth and shoulder-free resistance output during cyclic tensile testing and joint-motion monitoring. This behavior is associated with the combined contribution of conductive-filler network density and the GR/CNT hybrid architecture, which stabilizes conductive-pathway evolution and tunneling-distance recovery during cyclic deformation.