A novel phosphoramidate-based eco-friendly flame retardant for epoxy resins: enhanced mechanical properties and fire safety

The development of high-performance flame-retardant epoxy resins (EP) has attracted increasing attention. This work aims to address the concern for efficient and eco-friendly EP with enhanced fire resistance by synthesizing a novel phosphorus-nitrogen flame retardant, APDP. The flame retardant was synthesized through a one-step, solvent-free reaction between dimethyl methylphosphonate (DMMP) and aminoethylpiperazine (AEP). When only 2 wt.% of APDP was incorporated into EP, it significantly improved fire safety, achieving a limiting oxygen index (LOI) of 33.2% and a V-0 rating in the UL-94 test. Cone calorimetry tests (CCT) showed a 40% reduction in total heat release (THR) and a 26% reduction in total smoke release (TSR) compared to the control EP sample. Additionally, APDP improved the storage modulus and glass transition temperature of the EP composite, and enhanced its mechanical properties, with tensile strength increased by 5.6%, impact strength by 58.5%, and shear strength by 15.5%, while preserving the transparency of the EP samples. This work underscored the potential of APDP as an eco-friendly solution for improving both the flame retardancy and mechanical properties of epoxy resin, aiming to address critical fire safety challenges across various industry areas.