Synthesis of Novel Bio-Based Schiff Base Flame Retardant to Improve the Fire Safety of Epoxy Resin

Epoxy resin (EP) is widely used in engineering plastics, but its inherent flammability limits its broader applications. In this study, EDVAPC, a phosphorus and nitrogen-containing flame retardant, was synthesized through the Schiff reaction. Then it was incorporated into EP to enhance flame retardancy, which was used as a gas-phase and condensed-phase flame retardant. The results showed that the addition of EDVAPC maintained the good transparency of EP composites. Additionally, the maximum heat weight loss rate of EP-6%-EDVAPC reduced from 1.56%/°C to 1.31%/°C, indicating improved thermal stability. When 6 wt% EDVAPC was added to EP, the vertical combustion test (UL-94) rating achieved V-0, and the limiting oxygen index (LOI) increased to 31.2%. Compared to pure EP, the peak heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and peak smoke release rate (PSPR) decreased by 33.3%, 9.1%, 39.8%, and 25.3%, respectively. Importantly, the mechanical properties of EP were not compromised. The tensile strength remained, and the impact strength was increased by 5%.