9,10-Dihydro-9-Oxa-10-Phosphaphenanthrene-10-Oxide-Mediated Precise Interfacial Assembly Strategy of Bio-Based Polyphosphazene and Its Synergistic Flame-Retardant and Performance-Enhancing Effects in Epoxy Resins

A newly developed core-shell flame retardant, designated as DOPO-APP@HPZ, was synthesized and characterized.Utilizing the interfacial induction effect of 9,10-dihydro-9-oxa-10phosphaphenanthrene-10-oxide (DOPO), a uniform and dense coating of bio-based hyperbranched polyphosphazene (HPZ) was achieved on the surface of ammonium polyphosphate (APP).This flame retardant was incorporated within the epoxy resin (EP) matrix, and comprehensive evaluations were performed to assess the composites' flame retardancy, smoke suppression efficiency, mechanical strength, and ultraviolet (UV) resistance.The results revealed that the EP/DOPO-APP@HPZ composite exhibited superior overall performance relative to pure EP and composites containing APP or APP@HPZ.Specifically, the limiting oxygen index (LOI) surged to 28.7%, and the UL-94 flame retardant rating attained V-0 rating.Cone calorimetry results demonstrated significant declines in peak heat release rate (pHRR), total smoke production (TSP), and total heat release (THR) by 74.8%, 64.52%, and 45.2%, respectively, relative to pure EP, alongside marked suppression of smoke and toxic gas emissions.The flame retardant maintained the composite's mechanical integrity via good interfacial compatibility with EP, and also endowed it with excellent UV resistance, reduced dielectric constant and loss.Mechanistic studies verified its prominent gas-condensed phase synergistic flameretardant effects, providing a new strategy for multifunctional advanced flame-retardant EP composites.