Vanillin-Based Polyol Combined with Castor Oil to Fabricate Water-Borne Polyurethane with Recyclability and Self-Healing Properties for Fluorescent Ink and Flexible Sensor Applications

The development of environmentally friendly WPUs with sustainable biobased feedstock, repairability, recyclability, and multifunctionality is highly attractive and desirable. Herein, a vanillin-based polyol (VP) containing dynamic Schiff base bonds was synthesized via a one-step reaction. The rigid VP was combined with flexible castor oil, acting as polyols, to produce biobased waterborne polyurethanes (BWPU). The obtained BWPU material simultaneously possessed tunable mechanical properties (tensile strength up to 11.49 MPa, elongation at break reached 169.04%), high thermal stability (T₅ > 240 °C), self-healing properties (20 min at 150 °C), remolding properties (3 h at 150 °C), and chemical degradation properties (1 mol/L HCl solution), demonstrating excellent in-service performance and an attractive closed-loop recycling feature. Interestingly, the BWPU material exhibited obvious fluorescent properties, which can be used as fluorescent ink for information security. Furthermore, by incorporating conductive Ag nanowires, the potential application of BWPU as wearable flexible sensors was explored, and the prepared AgNW/BWPU flexible pressure sensors exhibited sensitive sensing ability with quick responsiveness (100 ms), which can be used to monitor both subtle movements and large human movements. This work provides a strategy for achieving repairable and recyclable BWPU with fluorescence and sensing properties.