Castor oil-based polyurethane based on hierarchical hydrogen-bonding strategy for water resistance, anti-corrosion properties, and rapid self-healing

Bio-based polyurethane (BPU), as an ideal alternative to traditional petroleum-based polymers, is generally faced with issues such as poor mechanical properties, short service life and insufficient stability, which limit its application in the field of high-end protection. This work proposes a multi-component regulation mechanism centered on hierarchical hydrogen-bonding and phase separation synergy, which balances the mechanical properties and self-healing performance of castor oil-based polyurethane (BPU-Px-Cy). By adjusting the ratio of soft-hard segments and rigid cellulose acetate, the hydrogen bond content of the BPU-Px-Cy series can be regulated to construct hard-phase microdomains. Notably, the optimal sample BPU-P2-C3 achieves a tensile strength of 10.5 MPa and an elongation at break of 94.59%. The abundant hierarchical hydrogen bonds within the system inhibits molecular chain crystallization, forming a stable amorphous structure that enables the material to achieve a light transmittance of 96.45%. Furthermore, by utilizing hierarchical hydrogen-bonding and long alkyl chains to construct a reversible molecular network, chain segments flow upon heating, enabling the material to self-heal completely within 90 s in water at 100 °C. The excellent hydrophobicity of the material (contact angle of 107.53°, swelling rate of 1.07% after soaking in water for 6.5 days) acts synergistically with the internal high-density cross-linked network, leading to a corrosion protection efficiency of 99.99% for steel plates. This work provides a new approach for the development of long-lasting smart protective coatings suitable for applications in metal corrosion protection, architectural decoration and optical protection.