Synthesis of the flame retardant DOPO-BZA and its enhancement of the flame retardancy in epoxy resin

To develop high-performance flame-retardant epoxy resin (EP), a novel phosphorus-nitrogen co-flame retardant, DOPO-BZA, was synthesized from benzylamine (BZA), paraformaldehyde (PFA), and 9,10-dihydro-9-oxaza-10-phosphame-10-oxide (DOPO) as precursors. The characterization of DOPO-BZA was conducted using FTIR and ¹H NMR techniques. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were employed to investigate the curing behavior and thermal stability of DOPO-BZA/EP composites. The flame retardancy and smoke suppression capabilities of these composites were evaluated, along with an analysis of their comprehensive properties. Flame retardant testing revealed that the EP achieved a UL-94 V-0 rating with only 4% DOPO-BZA incorporated. Additionally, the limiting oxygen index (LOI) for the DOPO-BZA-4/EP sample was measured at 32.8%. Furthermore, there was a reduction in peak heat release rate by 10.8%, while total heat release and total smoke production decreased significantly by 20.8% and 17.7%, respectively. This demonstrates that EP can attain optimal flame retardancy and smoke suppression performance even at low additive levels of the flame retardant. In addition, by adding only 4%DOPO-BZA, the tensile strength of the composite was increased by 43.6%. This study not only presents an innovative strategy for designing highly efficient flame retardants, but also enhances the overall properties of EP resins for practical applications.