Construction of TA/PEI@ZrP hybrids toward enhancement of dual-functional fire and UV resistance in composite coatings

Waterborne epoxy (EP) coatings are widely used for fire protection of steel structures due to their environmental friendliness and cost-effectiveness. Although significant progress has been made in the development of fire-retardant coatings, a key challenge remains regarding their long-term stability under harsh environments with strong ultraviolet (UV) radiation. To address this challenge, this study employed layered α-ZrP nanosheets as a substrate, polyethylenimine (PEI) as a bridging agent and tannic acid (TA) as a functional modifier, to prepare TA/PEI@ZrP hybrids via a Schiff base reaction. These hybrids were then incorporated into an EP intumescent fire-retardant coating to fabricate a TA/PEI@ZrP/EP composite coating. Accelerated aging tests demonstrated that the incorporation of TA/PEI@ZrP improved gloss retention and reduced the degradation of EP structures. Fire performance tests demonstrated that the composite coating exhibits excellent fire resistance. The Bronsted acid sites (BAS) of ZrP catalyzed the formation of a dense and high-strength intumescent char layer, which reduced the backside temperature of the steel substrate from 236.8 °C to 184.7 °C. The char expansion height and expansion ratio increased from 5.73 mm and 5.18 to 23.1 mm and 17.63, respectively. These results indicate that the composite coating exhibits both enhanced fire resistance and improved UV durability, leading to an overall improvement in protective performance. This work provides new insights into the design of multifunctional composite coatings with long-term stability and high-efficiency UV resistance.