Construction of phloretin-modified bio-based waterborne polyurethane network: Strong toughness, UV-blocking, and anticorrosion

The utilization of biomass resources for multifunctional bio-based waterborne polyurethane (WPU) development is receiving considerable attention. Phloretin (PRT) is considered to be a potential functional plant-based chain extender due to its unique molecular structure. Hereon, a commercial-grade castor oil-modified polyol was utilized as the soft segment. Through a molecular structure design strategy, PRT was incorporated into WPU skeleton to prepare a series of PWPU coatings with varying PRT contents. The results indicated that the addition of PRT resulted in a reduction in the length of cross-linking sites, an increase in the density of the cross-linking network, and significant enhancement of various properties, including mechanical properties, water resistance, adhesion, and anticorrosive performance. For instance, the PWPU-2 film exhibited a tensile strength of 38.2 MPa and an elongation at break of 608.8 %, while its toughness reached an even more remarkable value of 142.8 MJ/m³, surpassing all previously reported plant oil-based WPU systems. Interestingly, the water absorption rate of the PWPU-4 film decreased to 10.2 %, overcoming the challenge of simultaneously improving both water resistance and mechanical properties in plant oil-based WPU. Furthermore, the protective efficiency (IE) of the PWPU-10 coating reached up to 97.08 %. More importantly, the introduction of PRT had endowed PWPU coatings with a comprehensive range of UV shielding properties. The PWPU coatings prepared in this study have applications in various fields, such as anti-corrosion coatings, sunscreen coatings, and water-based ink connectors. These findings provided theoretical ideas for multifunctional WPU functional coatings.