Flexible and Stretchable Strain Sensor Integrated with a Supercapacitor Based on Coaxial Wet-Spun Polyurethane/Polypyrrole@poly(3,4-ethylenedioxythiophene)/Single-Walled Carbon Nanotubes Fibers.

Stretchable strain sensors integrated with supercapacitor functions have drawn significant attention due to their wide potential applications. In this study, a composite fiber with a core-shell structure is fabricated via a coaxial wet spinning method to enhance the comprehensive properties. The fiber uses thermoplastic polyurethane (TPU) and polypyrrole (PPy) as the shell layer and poly(3,4-ethylenedioxythiophene) (PEDOT) and single-walled carbon nanotubes (SWCNTs) as the core layer. By optimizing the contents of PPy, SWCNTs, and TPU, we obtain stretchable strain sensors with both sensing and electrochemical properties. The results show that when the content of PPy is 1.5%, that of SWCNTs is 0.7%, and that of TPU is 10%, the prepared composite fibers exhibit excellent mechanical and electrochemical properties, a stress of 65.7 MPa, a strain of 374.8%, and a mass-specific capacitance of 759.5 F/g. The strain sensors can accurately recognize human body movements in finger bending cycle tests and exhibit a high gauge factor (76.5, for the stretch range of 40-50%) and stable cyclic tensile response (4000 cycles), which indicates their good strain sensing properties.