Preparation and characterization of expandable graphite/silicone resin co-modified polyurethane-based intumescent flame retardant thermal insulation coatings

The expandable graphite (EG)/silicone resin co -modified polyurethane-based intumescent flame retardant thermal-insulating coating was prepared with polyurethane as the matrix, ammonium polyphosphate (APP) serves as the acid supplier, pentaerythritol (PER) acts as the char precursor, and melamine (MEL) functions as the gas generator, EG as the synergist, and silicone resin as the modifier. The effects of EG and silicone resin on the flame-retardant thermal insulation properties, thermal reaction mechanism, and component-structure evolution of the coatings were comprehensively discussed. The addition of EG increased the amount of char generated and solved the problem of serious melting droplets in the char layer during the expansion process. The addition of silicone optimized the internal structure of the char layer and ensured its structural integrity and thermal stability. When the addition amounts of EG and silicone resin were 7.5 % and 10 %, respectively, the coating SP3–4 exhibited the best performance. The temperature on the reverse side of the substrate with SP3–4 coating was lowered to 174 °C, and the anti-ablation time was increased to >2 h. The limiting oxygen index (LOI) of SP3–4 was 30.5 %, while that of blank coating Z6 was 23.8 %. Compared to the blank Z6, SP3–4 exhibited a 91 % decrease in smoke generation rate and a 70.4 % reduction in total smoke production, and the char residue rate at 1200 °C was increased by 355 %, the Brunauer-Emmet-Teller (BET) surface area of the char residue was increased by 287.9 %, and the tensile strength was increased by 63.1 %.