Vanillin-Based\nPolyol Combined with Castor Oil to\nFabricate Water-Borne Polyurethane with Recyclability and Self-Healing\nProperties for Fluorescent Ink and Flexible Sensor Applications

The development of environmentally friendly WPUs with\nsustainable\nbiobased feedstock, repairability, recyclability, and multifunctionality\nis highly attractive and desirable. Herein, a vanillin-based polyol\n(VP) containing dynamic Schiff base bonds was synthesized via a one-step\nreaction. The rigid VP was combined with flexible castor oil, acting\nas polyols, to produce biobased waterborne polyurethanes (BWPU). The\nobtained BWPU material simultaneously possessed tunable mechanical\nproperties (tensile strength up to 11.49 MPa, elongation at break\nreached 169.04%), high thermal stability (<i>T</i><sub>5</sub> > 240 °C), self-healing properties (20 min at 150 °C),\nremolding properties (3 h at 150 °C), and chemical degradation\nproperties (1 mol/L HCl solution), demonstrating excellent in-service\nperformance and an attractive closed-loop recycling feature. Interestingly,\nthe BWPU material exhibited obvious fluorescent properties, which\ncan be used as fluorescent ink for information security. Furthermore,\nby incorporating conductive Ag nanowires, the potential application\nof BWPU as wearable flexible sensors was explored, and the prepared\nAgNW/BWPU\nflexible pressure sensors exhibited sensitive sensing ability with\nquick responsiveness (100 ms), which can be used to monitor both subtle\nmovements and large human movements. This work provides a strategy\nfor achieving repairable and recyclable BWPU with fluorescence and\nsensing properties.