A phosphonitrile flame retardant for enhanced flame retardancy, smoke suppression and mechanical properties of epoxy resin

It is of great significance to enhance the fire safety of epoxy resins (EP), especially to reduce the release of heat and smoke. Therefore, in this work, flame retardants PNIM and PNDA were prepared and introduced into EP to achieve the effective suppression of heat and smoke. EP/DDM/PNDA-10 can self-extinguish quickly, achieving the V-0 rating as well as the LOI value of 34.3%. Compared with the Control EP, the peak heat release rate (pHRR), total heat release (THR), and total smoke production (TSP) of EP/DDM/PNDA-10 decreased by 68.7%, 36.2% and 35.7%, respectively. It can be attributed to the P/N synergistic flame retardant effect. During the combustion process, PNIM and PNDA can promote the formation of a dense carbon layer containing phosphorus and nitrogen, retain pyrolysis products in the condensed phase, and simultaneously inhibit the transfer of heat and oxygen. In addition, the PO· and PO 2 · free radicals produced by the decomposition of flame retardants can capture the active free radicals in the air, thereby interrupting the combustion reaction. Simultaneously, non-flammable gases, such as N 2 and NH 3 were released, which diluted the concentration of combustible volatiles and oxygen and enhanced the gas phase flame-retardant effect. Furthermore, EP/DDM/PNIM-10 exhibited excellent mechanical properties, with tensile strength and impact strength increasing by 33.1% and 131.4%. In general, this work provides an approach to developing a phosphonitrile flame retardant with broad applications in high-performance EP.