Trinity-cooperative flame-retardant strategy towards low flammability of epoxy resin: Phosphonate, imine and benzimidazolone

It is of great importance to endow flammable synthetic polymers like epoxy resins (EP) with fire safety, particularly to reduce the release of smoke and heat once being ignited. Hence, based on the cooperative strategy, a trinity-philosophy, that phosphonate with dehydrating-charring ability, Schiff base showing self-cross-linking at high temperature, and nitrogen heterocyclic ring with char-forming ability were integrated into one, was proposed in this work. Accordingly, an organic additive-type flame retardant named IMPP was prepared by combining phosphonate, aromatic Schiff base and benzimidazolone structures, and introduced into EP to achieve effective suppression of heat and smoke. The peak heat release rate (pHRR), total smoke production (TSP), and CO production rate (COP) were reduced by 72 %, 48 %, and 55 %, respectively. During burning, IMPP promoted the formation of a protective closed-cell char containing phosphorus and nitrogen in the matrix to retain pyrolysis products in the residue, inhibiting heat and mass transfer. Consequently, this work presents a novel approach for the rational design of phosphorus-containing flame retardants, primarily focused on condensed phase flame retardancy while also demonstrating effective smoke suppression.