A self-healing polypyrrole/oxidized natural rubber conductive composite as a building block for highly sensitive strain sensors

Wearable flexible strain sensors have attracted significant attention in human movements due to their high sensitivity, broad strain range and long-term stability. However, the fragility of the sensors limits their widespread applications. Here, a self-healing rubber-based conductive composite with excellent electrical conductivity and high sensitivity are prepared by in-situ polymerization of pyrrole in oxidized deproteinized natural rubber latex. Based on the hydrogen bonds between oxidized deproteinized natural rubber, polypyrrole and polyethylene glycol monolauryl ether, the composites show efficient self-healing behavior (η = 91.1%) under 50 °C for 24 h. The conductive composites containing 5 wt% polypyrrole perform excellent conductivity (3.5 S/m), fast response time (180 ms), low strain detection limit (1%), and long-term reliability (over 1500 cycles at 40% strain). The gauge factors are 3.2 at low strain (<60%) and up to 477.6 at large strain (>430%). Furthermore, the rubber-based conductive composites are fabricated as sensors to accurately monitor a variety of human joint movements (finger, wrist, elbow, and knee bending) and facial expressions (pouting, and winking).