Tannic Acid Coated with Magnesium Hydroxide and Nanoparticles of Fe-MOF for Applications as Flame Retardants and Increasing the Mechanical Durability of One-Component Polyurea Coatings

Abstract One-component polyurea (PUA) has attracted increasing attention as a protective coating material because of its excellent adhesion, outstanding corrosion resistance, and simple application process. Nevertheless, its intrinsic flammability, rapid heat release, and excessive smoke generation during combustion greatly restrict its use in fire protection applications. In this work, a hierarchical TA-MH/Fe-MOF nanohybrid flame retardant was constructed by functionalizing magnesium hydroxide (MH) with biomass-derived tannic acid (TA), followed by the assembly of Fe-MOF nanoparticles onto the TA-functionalized MH surface. The polyphenol-rich TA layer improved the interfacial compatibility between MH and the PUA matrix. It also provided abundant coordination sites for for Fe-MOF immobilization, thereby constructing a hierarchical nanoscale interface and improving filler dispersion. The incorporation of TA-MH/Fe-MOF significantly improved the flame-retardant performance of one-component PUA. Compared with neat PUA, the limiting oxygen index (LOI) of the composite increased to 22.4%. Meanwhile, the peak heat release rate (PHRR), peak smoke production rate (PSPR), total smoke production (TSP), and peak CO2 production (pCO2P) decreased by 42.18%, 32.08%, 50.00%, and 42.11%, respectively. Furthermore, the residual char yield increased significantly, and a more continuous and compact carbonaceous protective layer was formed during combustion. More importantly, the hierarchical nanostructure structure improved the dispersion of the flame retardant within the one-component PUA matrix. As a result, the composite maintained excellent mechanical properties while exhibiting enhanced corrosion resistance. This study provides a simple, environmentally friendly, and efficient strategy for developing high-performance one-component PUA protective coatings.