Environmentally Friendly Core‐Shell P/B‐g‐C 3 N 4 @Cu 3 P With Strong Interfacial Coupling Effect to Enhance Flame Retardant Properties of Biodegradable Poly (Butylene Adipate‐Co‐Terephthalate)

Developing excellent flame‐retardant biodegradable polymers is critical to high levels of fire safety. Herein, copper phosphide (Cu 3 P) is cleverly coated on the surface of P/B co‐doped g‐C 3 N 4 (PBCN) by an in situ self‐assembly strategy, denoted as PBCN@Cu 3 P. PBCN@Cu 3 P is added to poly (butylene adipate‐co‐terephthalate) (PBAT) to build an environmentally friendly core–shell flame retardant (PBAT/PBCN@Cu 3 P) by in situ hot‐melt method. The strong interfacial electron conjugation effect achieves a synergistic flame‐retardant mechanism of gas‐phase radical quenching and condensed‐phase carbon layer enhancement. As expected, the optimized the PBCN@ Cu 3 P/PBAT flame retardant peak heat release rate and total heat release decreased by 22.18% and 13.23%, respectively. Meanwhile, the fracture strength of the composite material remains above 127%. The mechanism of strong interfacial electron conjugation effect on catalyzing carbon formation and inhibiting toxic fumes is investigated by flame retardant characterization and density functional theory calculations. This work provides new insights for the development of efficient, environmentally‐friendly, multifunctional bio‐based flame retardant systems.