Sustainable, transparent, strong toughness, UV resistance, and anti-corrosion properties of cashew shell oil-based waterborne polyurethane network derived from phloretin and sorbitan monooleate-based siloxane

The increasingly severe energy shortage and growing environmental problems have accelerated the rapid development of sustainable polymer materials. Hereon, a novel method was proposed for the synthesis of cashew nut shell oil-based waterborne polyurethane (WPUs), which exhibited excellent toughness, transparency, water resistance, UV resistance and corrosion resistance. Specifically, the sorbitan monooleate-based siloxane (MSP) was prepared via a thiol-ene click chemistry reaction. Subsequently, the plant-based phloretin (PRT) and MSP were introduced as polyols into the skeleton of WPUs through the molecular structure design strategy. Series of high bio-based content (91 %) WPUs networks were obtained via pre-polymerization and self-emulsification methods. The properties of their dispersions and films were thoroughly investigated, and it was found that the addition of MSP and PRT enhanced the overall performance of WPUs film. For instance, there was a significant increase in T_g. Additionally, they exhibited a maximum tensile strength of 31.5 MPa and a maximum toughness of 53 MJ/m³, which were the most outstanding among all reported plant oil-based WPU systems so far, indicating excellent tear resistance. Interestingly, the water absorption rate of PSWPU-40 was reduced to 7.1 %, suggesting good water resistance, which resolved the contradiction between the mechanical properties and water resistance of the current plant oil-based WPU systems. The PSPWU films exhibited promising application prospects, exemplified by its ability to effectively shield the entire UV range. Furthermore, its coating demonstrated outstanding anti-corrosion properties with a maximum anticorrosion efficiency of 97.1 %. It could be attributed to the synergistic effect of a self-crosslinking structure, higher crosslinking density, a tighter network structure, and stronger intermolecular forces (H-bond). This work provided a meaningful guide for the application and development of high-performance bio-based WPU functional coatings.