Development of Phosphorus‐Doped Carbon Nitride‐Coated Ammonium Polyphosphate Flame Retardant and Its Effect on the Fire Safety of Epoxy Resins

ABSTRACT Epoxy resin (EP) is widely used in fields such as building materials, aerospace, and transportation; however, its high fire risk is considered the main factor limiting its practical use. To address this issue, ammonium polyphosphate (APP) is coated with phosphorus‐doped graphitic carbon nitride (PCN) to prepare PCN@APP. When compared with pure EP, the composite with high‐loading APP is observed to exhibit reduced mechanical properties. In contrast, the composite containing modified APP is shown to demonstrate enhanced mechanical performance. Specifically, the flexural strength and tensile strength are increased by 9.13% and 45.09%, respectively. With the incorporation of 20 wt% PCN@APP, significant reductions are achieved in key fire parameters: the peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), total smoke production (TSP), peak CO production (PCOP), and peak CO 2 production (PCO 2 P) are lowered by 66.6%, 66.2%, 71.8%, 78.7%, 65.5%, and 68.6%, respectively. TG‐IR results indicate that after adding the PCN@APP filler, the absorbance of CO and NO is reduced by 80.2% and 67.9%, respectively, demonstrating significant suppression of fire toxicity. This work is considered to provide valuable inspiration for the straightforward design of APP‐based flame retardants, thereby enhancing their flame‐retardant efficiency.