Improving the flame retardancy of epoxy resin by incorporating a novel vanillin-based flame retardant

Traditional bisphenol A epoxy resin was modified with a vanillin-based flame retardant by facial blending method. The effects of vanillin-based flame retardant on the thermal stability, flame retardancy, and mechanical properties of epoxy resin were investigated by thermogravimetric analyzer, limiting oxygen index tester, cone calorimeter, and dynamic thermomechanical analyzer. The results demonstrated that the thermal stability and flame retardancy of epoxy thermosets were significantly improved, but the mechanical properties were slightly decreased. When the amount of vanillin-based flame retardant was 10 wt%, the limiting oxygen index was increased from 25.2 % to 30.1 %, the total heat release of modified epoxy was reduced from 82.1 MJ/m2 to 60.2 MJ/m2, and the total smoke production was reduced from 28.9 m2 to 20.8 m2. And the average effective heat of combustion was reduced from 22.3 MJ/kg to 20.2 MJ/kg. When the vanillin-based flame retardant content was 20 wt%, the maximum smoke density of modified epoxy thermosets was reduced by 40.1 % in comparison with pure epoxy thermosets. The self-crosslinking reaction of Schiff base groups promoted the formation of char layer, which reduced the thermal decomposition of epoxy matrix and smoke release, thus significantly reducing the fire hazard. The modified epoxy resin showed a tensile strength of 57.1 MPa, flexural strength of 71.6 MPa, and glass transition temperature of 153.1 °C, which were higher than those of commercial petroleum-based bisphenol A epoxy resin (51.5 MPa, 64.3 MPa, 150.6 °C). This work promotes the application research of bio-based flame retardants in fire safety of polymers.