Self-Healable, Degradable, and Reprocessable Lignin-based Polyurethane Elastomer for a Flexible Strain Sensor

Flexible strain sensors have attracted great attention for their important application potential in soft robot, wearable device, electronic skin, and human-computer interaction, yet there are still challenges such as the loss of service life by external force and produced electronic waste that need to be solved. Herein, a self-healable, degradable, and reprocessable lignin-based polyurethane (LPU) elastomer was synthesized for a flexible strain sensor. Owing to the formation of a cross-linking network by lignin and the reinforcement role of unreacted lignin, the tensile strength and elongation at break of the LPU elastomer reached 2.72 MPa and 712%, respectively. The plentiful hydrogen and disulfide bonds endowed the elastomer with not only good self-healing capability but also superior reprocessing performance. Importantly, the elastomer was able to be completely degraded within only 2 h in 1 mol L-1 NaOH water/ethanol solution. The LPU elastomer-based flexible strain sensor with liquid metal (LM) as the conductive material was successfully applied to detect various human motions and could restore its sensing function with the healing of the substrate and reconnection of the LM conductive layer. Moreover, the LM in the discarded sensor could be easily recycled to prepare the sensor after the degradation of the LPU substrate. The functional and environmentally friendly biobased elastomer will greatly promote the sustainable development and application of flexible electronics.