A robust P-N-Si synergistic flame retardant epoxy coating for wood building material protection

Wood is widely used in the construction and furniture industries due to its high strength-to-weight ratio, sustainability, and renewability. However, its inherent flammability poses significant safety risks. This study prepared a novel green and efficient P-N-Si flame retardant (PNSF) by modifying ammonium polyphosphate and tetramethylammonium polysilsesquioxanes (4CH₃-NH₃-POSS), which was applied to epoxy resin (EP) to prepare a flame retardant modified EP coating (EP/PNSF) for wood protection. The coating exhibited excellent flame retardancy and wear resistance, significantly enhancing the fire safety of wood. Vertical burning and limiting oxygen index (LOI) tests showed that adding 15 wt% PNSF increased the LOI of the EP from 22.8 % to 31.8 %, achieving a UL-94 V-0 grade. The formation of a relatively dense expanded carbon layer significantly improved flame retardancy, reducing the peak heat release rate by 37.5 %, total heat release rate by 43 %, and effective heat of combustion by 83.8 %. Additionally, the coating also had significant wear resistance, maintaining its hydrophobicity even after withstanding 100 wear cycles. This multifunctional flame retardant coating provided a promising strategy for improving the fire safety of wood building materials.