Multi-element synergistic effect based on functionalized porphyrin organic frameworks: Towards for promoting fire safety of epoxy

Epoxy resins (EP) is classic thermosetting material, but its flammability severely limits its usage. In this paper, a novel flame retardant (FePor@PZS) was synthesized by growing polyphosphazene (PZS) in situ onto the surface of iron porphyrin organic frameworks (FePor). Attributed to the synergistic flame retardant system of nitrogen, phosphorus and iron elements, FePor@PZS endowed excellent fire safety property to EP. Upon incorporating 2 wt% FePor@PZS, EP/FePor@PZS got an LOI value of 27.3%, achieving the V-1 level in the test of UL-94. Besides, the peak rate of heat release, release of total heat, peak rate of smoke production, production of total smoke, peak rate of CO₂ production and peak rate of CO production of EP/FePor@PZS were decreased by 31.8%, 21.5%, 17.5%, 22.3%, 34.8% and 73.5%, respectively, and the quantity of residual carbon increased from 9.69% to 27.86%, compared with neat EP. FePor could break off to form a single pyrrole ring to promote the generation of the early carbon layers. Additionally, the Fe element in FePor and the P element in PZS played a role of catalytic carbonization. Meanwhile, PZS could decompose into non-combustible gases, and produce PO• and HPO• radicals to terminate the EP chain-opening reaction. This research gives a novel approach for the application of porphyrin derivatives in flame retardant composites.