Flexible, recyclable and sensitive piezoresistive sensors enabled by lignin polyurethane-based conductive foam

Flexible sensors are of great significance in wearable electronic devices. Herein, this work solves the problems of unfriendly and high cost materials and not easy to recycle conductive parts. Multi-functional conductive polyurethane (PU) foam has been constructed based on lignin, PU, and MWCNTs. Lignin is widely available and environmentally friendly, which endows polyurethane foam with degradable properties. The sensor exhibited excellent resistance change performance in the ultra-wide compression range from 0 to 90%. After 2000 cycles of compression test, the resistance change curve was still stable, and then the resistance returned to the initial value. The detection pressure was as high as 275.95 kPa. This sensor can detect a minimum deformation of 0.23%. The gauge factor value is as high as 2.75 in the strain range of 30% to 60% of compression deformation. It does not change shape under 90% cyclic compression strain, and does not change micro surface morphology after washing in distilled water for 12 hours. The sensor can not only detect large-scale movements of human limbs and joints but also detect weak physiological activities such as mouth opening, swallowing, breathing, and pulse. At the same time, it has good repeatability and reproducibility for throat vibration caused by human pronunciation and for some non-contact movements (such as blowing and vibration). Finally, because MWCNTs@LPUF is degradable in an alkaline environment, MWCNTs can also be recycled and used. MWCNTs@LPUF sensors are environmentally friendly, recyclable, sensitive and have excellent environmental stability, enabling them to have great potential for future application in the fields of flexible wearable electronics and healthcare.