Preparation of a multifunctional flame retardant epoxy resin containing phosphorus and nitrogen and study of its properties

A highly reactive intrinsic epoxy flame retardant FREP was successfully synthesized via ring-opening reaction between DOPO and amino-tetrafunctional epoxy resin (AG-601), and the structure of the synthesized FREP was characterized by FTIR and MS. FREP was then introduced into the epoxy resin as an additive, aiming to improve fire safety. The flame-retardant properties and thermal stabilities of epoxy thermosets were investigated by limiting oxygen index (LOI), vertical burning test (UL94) and cone calorimetry (CONE). The results indicated that EP/FREP-4 thermoset passed UL94 V-0 rating with a LOI value of 34.6%, where the phosphorus content was 1.5 wt%. When compared with neat EP, the peak heat release rate (pk-HRR), total heat release (THR) and total smoke production (TSP) decreased by 63.1%, 42.6%, and 22.1%, respectively. Meanwhile, the lower av-EHC of EP/FREP thermosets indicated that FREP plays a significant role in gas-phase flame retardancy. Additionally, DMA analysis showed that FREP improved the crosslinking density of EP, which had little effect on the glass transition temperature (T-g). Thermogravimetric analysis (TGA), Py-GC/MS analysis, and SEM were used to investigate the flame retardant mechanism. Excellent flame retardancy was attributed to phosphorus and nitrogen's synergistic effect in the gas and condensed phases.