Synergistic Flame Retardancy and Thermal Stability in Epoxy Resins Achieved by a Phosphorus‐Based Schiff Base Under <scp>DNEA</scp> Co‐Curing

ABSTRACT Epoxy resin (EP) is widely used in construction, aerospace, and electronics to enhance product safety and prevent fire hazards. However, it is hard to balance flame retardancy, heat resistance, and the mechanical properties of the EP matrix during production. In this paper, a novel halogen‐free phosphorus‐based EP composite featured with high flame retardant and heat resistance, was successfully synthesized by introducing a co‐curing agent, namely a halogen‐free phosphorus‐based flame retardant, designated as DNEA into the EP matrix. It is found that the coke output of the resulting EP composite at 600°C can even be raised by 100% with an 8 wt% dosage of DNEA. Moreover, the sample possesses the limiting oxygen index (LOI) of 29.5% and meets the UL‐94 V‐0 flammability rating. In addition, the heat release rate (HRR) and total heat release (THR) of the phosphorus‐based EP composite were reduced greatly by 30.3% and 19.1%, respectively. Owing to the good compatibility between DNEA and EP, the phosphorus‐based EP composite exhibited a high tensile strength of 87.5 MPa and a high tensile modulus of 2916 MPa. Therefore, the phosphorus‐based EP composite in this paper is expected to be applied in high‐temperature resistant insulating coatings, electronic packaging materials, and related fields.