Thermal-Driven Self-Healing Polyurethane Based on Polydopamine Nanoparticles with Enhanced Mechanical and UV Shielding Properties

Ultraviolet (UV) shielding materials have garnered widespread applications in biological protection, aerospace, intelligent coating, and other fields. However, they are vulnerable to external friction scratches due to prolonged exposure, which leads to a decline in their UV shielding ability, further limiting their long-term applications. In this work, a series of waterborne polyurethane–polydopamine nanocomposites with excellent self-healing and UV shielding properties were prepared, among which using waterborne polyurethane with Diels–Alder thermally reversible cross-linked networks as the substrate and polydopamine (PDA) nanoparticles as the UV shielding agent. The developed nanocomposites can achieve a good self-healing effect at 120 °C in 30 min, and the self-healing efficiency can reach more than 68%. Adding PDA nanoparticles can enhance the mechanical and UV shielding properties of the nanocomposite. The nanocomposite with 0.5 wt % PDA contents has both the highest tensile strength and elongation at break, with values of 9.9 MPa and 667.27%, respectively. UV–vis tests exhibit that the residual amount of methylene blue solution under the protection of the nanocomposite film containing 2 wt % PDA content could reach 63.81%, concluding that the as-prepared nanomaterials have excellent UV shielding properties. This study offers an idea for the production of excellent and durable UV shielding materials with self-healing properties.