LED/moisture dual-curable polyurethane acrylate coatings combine rapid formation by photocuring with complete secondary curing by moisture. They can therefore mitigate incomplete curing in colored systems, thick coatings, and the shadow regions of complex geometric components, showing broad application prospects in high-end coatings and electronic protection. However, such coatings are generally flammable, and the difficulty in balancing flame retardancy with mechanical properties remains a technical bottleneck restricting their further development. To this end, based on molecular structure design, this study synthesized a flame retardant (HBH) containing photoreactive groups and introduced it into a dual-curable polyurethane acrylate system, thereby preparing a series of dual-curable flame-retardant coatings (HBHx-HPPy) with different HBH contents. The effect of HBH content on the flame retardancy, mechanical properties, curing behavior, and surface properties of the coatings was systematically investigated. The results indicate that the incorporation of HBH significantly enhanced the comprehensive properties of the coatings. At an HBH content of 30 wt%, the corresponding HBH3-HPP4 cured specimen achieved a V-0 rating in the UL-94 test, and its limiting oxygen index (LOI) increased by 49.5% compared with HBH0-HPP7. Meanwhile, the peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), and total smoke release (TSR) were reduced by 30.5%, 40.7%, 52.4%, and 35.1%, respectively. Furthermore, the coating exhibited excellent mechanical properties and curing characteristics: a tensile strength of 15.35 MPa, a shear strength of 3.4 MPa, a gel fraction of 95.2%, and a curing depth of up to 8.16 mm after LED/moisture dual curing; in terms of surface properties, it achieved a 5B adhesion rating and a hardness of 69 D. The dual-curable polyurethane acrylate coating designed and prepared in this study effectively enhances the flame-retardant performance of the material while maintaining favorable mechanical properties and curing characteristics. This enables it to demonstrate promising application potential in the field of flame-retardant protective coatings with complex curing requirements, such as pigmented systems, thick layers, or shadowed areas.
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.
