Synthesis of a novel phosphazene-based flame retardant with active amine groups and its application in reducing the fire hazard of Epoxy Resin

A novel compound containing active amine groups of polyphosphazene (PBFA) was successfully synthesized and applied as a reactive flame-retardant additive in epoxy (EP) resin. It was synthesized from N-aminoethylpiperazine and hexachlorocyclotriphosphazene using a simple method, and its structure was well-characterized. The results indicated that introducing PBFA into EP composites significantly improves the resistance to fire and suppresses smoke generation. An EP composite with 9.0 wt% PBFA can pass the vertical burning tests V-0 rating, the peak heat release rate and total heat release of the sample decreased by 46.7% and 29.3%, respectively. Moreover, it decreased the total smoke release by 48.0%. Thermogravimetric analysis showed that the presence of PBFA can accelerate EP decomposition at comparatively low temperatures and lead to the formation of a stable char layer, which protects the matrix from fire, therefore improving the amount of char residue at 800 °C. The degree of small molecule degradation characterized by gas chromatograph/mass spectrometer, which was lower than that of pure EP, demonstrating that PBFA reduces the risk of fire. The glass transition temperature of EP composites increased with the amount of PBFA increasing owing to the presence of active amine groups. Notably, its mechanical properties were not degraded.