An interpenetrating polymer networks structure formed by in situ crosslinking of flame retardant for improvement in mechanical properties and flame retardancy of epoxy resins

Abstract Epoxy resins (EPs) possess flammable characteristics inherently, and various methods have been utilized to enhance their flame retardancy. However, the improvement of flame retardancy may reduce its mechanical properties at the same time. Hence, this work synthesized a novel interpenetrating polymer network structure by introducing double bonds into flame retardants based on crosslinking strategy. When the flame retardant was crosslinked inside the EPs, the increased crosslink density improved the mechanical properties and the fire retardancy of the EP thermosets. With the addition of just 3 wt% of a crosslinked flame retardant, its vertical combustion achieved grade V‐0 and had a limited oxygen index of 31.8%. In the cone calorimeter test, the heat release rate was significantly decreased by 56.7% compared with pure EP when the crosslinked flame retardant reached 5 wt%. The study on the pyrolysis behavior of the material and the residual char further revealed that the flame retardant has a biphasic flame‐retardant effect.