Study on electromechanical property of polypyrrole-coated strain sensors based on polyurethane and its hybrid covered yarns

Fiber-based flexible electronics have become one of the most demanding sensing elements by various wearable applications. However, many of those flexible electronics are facing the major challenge of high electromechanical hysteresis. In this paper, polypyrrole-coated strain sensors based on polyurethane yarns and hybrid polyurethane yarns were fabricated and tested. To lower the mechanical and electromechanical hysteresis of the yarn and yarn-based sensors, micro-morphology and electromechanical property of the yarn-based sensors were observed and analyzed, especially the existence and generation of cracks on conductive films of the sensors. The effect of the covered yarn structure on the electromechanical property of the sensors was discussed. Through the results of tensile tests, the electromechanical properties of the yarn-based sensors were characterized, with contributing factors of electromechanical hysteresis examined and reason for the nonlinear electrical resistance-strain relationship elaborated. Furthermore, the covered yarn structure was found stable, with fewer cracks under tension. It's recommended that hybrid PU yarns and corresponding yarn-based sensors shall be firstly considered for future research, for relatively small mechanical and electromechanical hysteresis. (C) 2020 Elsevier B.V. All rights reserved.