Synthesis of bio‐based reactive N/P flame retardant and its curing and flame retarding behavior in epoxy resins

Abstract

In this study, a pioneering bio‐based nitrogen–phosphorus flame retardant and curing accelerator named oxime‐phosphazene hexakis [(4‐(hydroxyimino) 2‐methoxy) phenoxy] cyclotriphosphazene (HAPV) was successfully synthesized using hexachlorocyclotriphosphazene and vanillin. When 5 wt % HAPV was added into epoxy, the limiting oxygen index increased from 22% to 27% and passed UL‐94 V‐0 (UL is defined as Underwriters Laboratories) rating. Meanwhile, with the addition 5 wt% HAPV, the apparent activation energy (Ea) of HAPV/EP decreased from 20.22 to 67.15 kJ/mol, and the pHRR value was suppressed from 581.21 to 330.18 kW/m2. It was due to that the HAPV quenched the combustion chain reaction through the gas phase and condensed phase, forming a dense char layer for blocking the heat transfer. Overall, the study provides an environmentally friendly epoxy flame retardant curing accelerator that shows great potential in epoxy flame retardant applications.