A Highly Effective, UV-Curable, Intumescent, Flame-Retardant Coating Containing Phosphorus, Nitrogen, and Sulfur,...

In this paper, a flame-retardant, UV-cured coating was prepared on the fiber composites' (FC) surface via a thiol-ene click reaction using pentaerythritol tetra(3-mercaptopropionate) (PETMP), triallyl cyanurate (TAC), and 2-hydroxyethyl methacrylate phosphate (PM-2). The synergistic effectiveness of phosphorus (P), nitrogen (N), and sulfur (S) was studied in detail by changing the proportion of these reactants. Sample S₄(N₃P₂)_6, with a molar ratio of N and P elements of 3:2, and the thiol and vinyl groups of 4:6 had the highest LOI value (28.6%) and was self-extinguishing in the horizontal combustion test. It had the lowest peak heat release rate (PHRR) value (279.25 kW/m²) and total smoke production (2.18 m²). Moreover, the thermogravimetric analysis (TG) showed that the decomposition process of the coated composites was delayed. The conversion rate of the double bond and the thiol of S₄(N₃P₂)₆ was 100% and 92.0%, respectively, which showed that the cross-linked network structure was successfully formed. The tensile strength and the flexural strength of coated composites improved, and the transparency of the coating can reach 90%. These characteristics showed that the UV-cured coatings could be used in industrial production to effectively prevent fires.