Simultaneously self-healing and photoluminescence waterborne polyurethane coatings based on dual dynamic bonds

Waterborne polyurethane coatings capable of excellent transparency, solvent resistance and hardness, have been widely used in furniture, leather and other industries. However, waterborne polyurethane used as coatings may be inevitably damaged during long-term use, which has bad effect on their service life. Therefore, it is of great significance to prepare self-healable waterborne polyurethane coatings with high strength, as well as other new functions. In this work, a class of carboxyl-type waterborne polyurethanes (CWPU) was facilely prepared. The average hydrodynamic diameter size and dispersion index of the prepared CWPU were 56 nm and 0.219, showing uniform size distribution and stable emulsification system. The key point of this work is using polymine (PEI), whose molecular structure containing primary amine and secondary amine can form ionic bonds and hydrogen bonds with CWPU. PEI can be introduced as crosslinking agent to prepare cross-linked CWPU (WPUs). The tensile strength and the elongation at break of WPUs can arrive at 17.12 MPa and 512.25%. After self healing at 30 degrees C for 24 h, the tensile strength and elongation at break of the WPUs can reach 3.26 MPa and 450.94%, respectively. Importantly, these synthesized WPUs not only have outstanding mechanical properties, but also exhibit excellent self-healing performance. Additionally, as for coatings, the visible light transmittance of prepared WPUs coatings is all higher than 75%, showing excellent optical properties. Especially, incorporating carbon quantum dots (CQs) can endow these prepared WPUs with obvious photoluminescence performance. The aforementioned functions of self-healing and photoluminescence performance have expanded the service life and application of WPUs coatings. This kind of coatings is expected to be used in plexiglass protective coating, light emitting diode, road signs, optical anti-counterfeiting and other fields.