Flame retardant behavior of bio-based epoxy resin bearing pyridazinone and dynamic ester bond via self-blow-out and vesicular carbon formation.

• Flame-retardant effect of pyridazinone on bio-based epoxy resin was detected. • Strong yet tough N-rich hollow vesicles were formed via "radical capturing" effect. • Potential for high value-added conversion from resin carbon to functional carbon. Aromatic nitrogen heterocyclic structure is a key building block of high-performance polymer materials and nitrogen-doped porous carbons, yet systematic studies on its flame-retardant effects and carbonization mechanisms in thermoset materials is still lacking. Here, a pyridazinone embedded bio-based epoxy resin (CSPZ-EP) cured by 4,4ʹ-methylenedianiline (DDM) was prepared. Benefiting from the rigid biphenyl-like pyridazinone structure and the high cross-linking density originated from the self-catalyzed transesterification, the cured CSPZ-EP/DDM can easily pass the UL-94 test with a V-0 rating suggesting excellent intrinsic flame retardancy. The cone calorimeter results further demonstrated that the peak heat release rate, the total heat release and flame growth rate of CSPZ-EP/DDM were significantly reduced by 84.4 %, 28.4 % and 90.5 %, respectively, compared with those of bisphenol A epoxy resin. The higher graphitization degree of the char residues and a large amount of non-flammable pyrolysis gas ejection synergistically prevented the further spread of fire. Strong yet tough nitrogen-rich char layer formed after thermal ablation together with the renewable features and the facile preparation route of CSPZ-EP/DDM make it a potential precursor for heteroatom porous carbons. [ABSTRACT FROM AUTHOR]