CNTs-coated TPU/ANF composite fiber with flexible conductive performance for joule heating, photothermal, and strain sensing

Flexible and highly conductive fiber has attracted considerable attention with its massive potential in functional fabric, stretchable circuits, and wearable electronic devices. Herein, we prepared a novel secondary structure composite fiber based on aramid nanofibers (ANF)-reinforced thermoplastic polyurethane (TPU) fiber accompanied by carbon nanotube (CNT)-coated on its surface. The composite fibers' dispersibility, micromorphology, and application were systematically investigated. The TPU/ANF-0.5 wt% sample showed a robust reinforcing effect, as Young's modulus and tensile strength reached 17.2 and 20.2 MPa, respectively. Meanwhile, the conductive coating layer in the outer frame was formed via a TPU solution with 10 wt% CNT content, which gives the fiber excellent flexible electrical conductivity. Such a unique structural design enables the fiber to be closely attached to human skin and monitor human movement. In addition, this TPU/ANF@CNT composite fiber can also be used for light and electric heating. The photothermal equilibrium temperature can reach 120°C in 50 s, and the electrothermal equilibrium temperature increases to 62°C under 30 V. In summary, this secondary structure composite fiber with excellent electrical and mechanical properties might have great practical application potential in wearable electronic devices.