Enabling High Strength and Toughness Polyurethane through Disordered‐Hydrogen Bonds for Printable, Recyclable, Ultra‐Fast Responsive Capacitive Sensors

The rapid advancement of smart, flexible electronic devices has paralleled a surge in electronic waste (e-waste), exacerbating massive resource depletion and serious environmental pollution. Recyclable materials are extensively investigated to address these challenges. Herein, this study designs a unique polyurethane (SPPUs) with ultra-high strength up to 60 MPa and toughness of 360 MJ m^-3. This synthetic SPPUs can be fully recycled at room temperature by using green solvents of ethanol. Accordingly, the resultant SPPU-Ni composites, created by mixing the ethanol-dissolved SPPUs solution with nickel (Ni) powder, effectively combine the flexibility and recyclability of SPPUs with the electrical conductivity of the nickel filler. Notably, this work develops the printable capacitive sensors (PCBS) through transcribing the paste of SPPUs-Ni slurry onto PET film and paper using screen-printing technology. The devised PCBS have fast response time ≈50 ms, high resolution, and multiple signal recognition capabilities. Remarkably, SPPUs and Ni powder can be fully recycled by only dissolving the waste PCBS in ethanol. This work offers a sustainable solution to the growing e-waste problem in recyclable flexible electronics.