A bio‐based reactive P/N synergistic flame retardant for improving the fire safety and mechanical properties of epoxy resin

A high‐efficiency bio‐based P/N synergistic flame retardant (PVFD) is synthesized by combining furfurylamine and vanillin. The compound incorporates two different valence states of phosphorus as flame retardant structures, namely phenylphosphoryl dichloride (PPDC) and 9,10‐dihydro‐9‐oxa‐10‐ phosphophenyl‐10‐oxide (DOPO). PVFD and epoxy resin (EP) can cure into a cross‐linked network, thus not only improving the mechanical properties of EP but also achieving P/N synergistic flame retardant effects. Experimental results demonstrate that EP/PVFD‐5 obtained by adding 5 wt% of PVFD to EP passes the UL‐94 test and achieves V‐0 grade, whose limiting oxygen index (LOI) is up to 38.0%. EP/PVFD‐5 exhibits a decrease of 10.14% in peak heat release rate (PHRR), 16.90% in total heat release (THR), and 10.0% in total smoke release (TSP), while the residual carbon content increases by 8.5%. Additionally, the bending strength, bending modulus, tensile strength, and elongation at break of EP/PVFD‐5 increase by 3.9%, 4.9%, 45.1%, and 26.3%, respectively.Highlights The bio‐based raw materials we used are eco‐friendly and readily available. PVFD, an efficient P‐N synergistic compound, was synthesized. PVFD promotes the char formation of EP and dilutes the O2 concentration. PVFD does not cause the degradation of mechanical properties of EP.