A gas-phase/condensed-phase synergistic flame retardant strategy towards high-efficiency fire safety of epoxy composites

In this study, phosphorus-containing flame retardant (PDA) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and protocatechualdehyde through simple chemical reactions, and subsequently employed as additive for the flame-retardant modification of epoxy resin (EP). The experimental results show that when the addition amount of PDA is 5 wt%, the peak heat release rate (pHRR) and total smoke emission (TSP) of the composite are significantly reduced by 50.9 % and 33.7 % respectively compared with pure EP, and it has successfully passed the UL94 V -0 rating. This excellent flame-retardant performance primarily stems from the synergistic interaction between the DOPO and protocatechualdehyde structural units in the PDA molecular architecture. The mechanism operates through a dual-action approach: radical scavenging to inhibit combustion chain reactions, and catalyzing the formation of a robust char layer that effectively impedes heat and oxygen transfer.