A novel polyaromatic ring phosphor-nitrogen imidazole derivative endowing epoxy resin with remarkable flame retardancy and mechanical properties

A novel flame retardant of polyaromatic ring phosphor-nitrogen imidazole derivative (PNB) was prepared and added to epoxy resin (EP) to develop epoxy resin thermosetting materials (PNB/EP) with excellent comprehensive properties. The peak temperature (T p ) and apparent activation energy (E) of PNB/EP-10 were lower than those of EP-0, indicating that PNB could catalyze the curing process. Moreover, PNB/EP had remarkable mechanical properties in addition to its outstanding fire safety. Concretely, the LOI of PNB/EP-10 was 37.9% and could reach V-0 level in UL-94 test. The total heat release (THR) and peak heat release rate (PHRR) were reduced by 34.6% and 36.6%, in comparison with the EP-0, respectively. Since the PNB structure contained nitrogen and phosphorus elements, which could reduce the fire risk of the polymer in both the gas and condensed phases, further improving the flame retardancy of the composite. Furthermore, PNB/EP had significant mechanical properties because PNB not only contained a polyaromatic ring structure capable of forming π-π bonds, which enhanced the interaction between the epoxy resin matrix and PNB, but the -NH structure also contributed to its dispersibility in the epoxy resin. This was reflected in the fact that the impact strength, tensile strength as well as flexural strength of PNB/EP-10 had increased by 22.5%, 47.1% and 34.5%, respectively. All the results indicated that PNB/EP overcame the inherent flammability and brittleness of epoxy resins and increased their curing activity, which had broadened their industrial applications.