Synthesis and Application of Bio-Based DOPO Derivatives for Enhancing Flame Retardancy and Mechanical Properties of Epoxy Resin

Epoxy resins (EP) have significant application value in the industrial sector; however, their flammability and toxic fume emissions during combustion limit their applications. Bio-based flame retardants provide effective flame-retardant properties, primarily owing to their unique molecular compositions and structural features. In this study, a flame retardant (DAVN) is prepared using vanillin, 5-amino-1H-tetrazole, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). When 6 wt.% DAVN is added to the EP, the EP composite exhibits a residual carbon content of 19.9% at 700°C while achieving a limiting oxygen index (LOI) value of 32.6% and the UL-94V-0 standard. Additionally, compared with pure EP, the peak heat release rate (PHRR), total heat output (THR), total smoke production (TSP), and smoke production rate (SPR) decrease by 49.3%, 44.7%, 35.1%, and 35.1%, respectively. These improvements primarily result from the polyphosphates formed from the DAVN decomposition, which promote the carbonization and cross-linking of EP, thus forming a compact carbon layer that suppresses heat and smoke release. Moreover, the formation of gas during combustion dilutes the combustible gases, thereby enhancing flame retardancy. Additionally, DAVN improves the mechanical properties of EP and increases its tensile strength by 7.1%. This study provides a useful reference for the development of high-performance flame-retardant EP composites. Graphical A bio-based flame retardant was synthesised using vanillin and DOPO as primary raw materials. This flame retardant demonstrated excellent flame-retardant properties in epoxy resins, offering a novel approach to enhancing the flame retardancy of epoxy resin composites.