Synthesis of a novel nonflammable eugenol-based phosphazene epoxy resin with unique burned intumescent char

Abstract Developing bioresourced epoxy resin with excellent flame retardancy is challenging for satisfying environmental and fire hazard requirements. Herein, a novel monomer with six functional epoxy groups was successfully synthesized by combining eugenol with hexachlorocyclotriphosphazene. Using aliphatic diamine as a curing agent, a novel epoxy of EHPE-D230 was prepared, and its properties were systematically evaluated. Compared with commercial epoxy resin (E51-D230), EHEP-D230 possessed a higher tensile strength (56.7 to 64.2 MPa) and better thermal resistance (Tα = 85 to 119 °C). Moreover, EHEP-D230 exhibited a high limiting oxygen index value of 31%, and it passed the UL94 V-0 test without any after-flame time. Cone calorimeter test indicated that the peak value of the heat release rate, total heat release, and total smoke production for EHEP-D230 reduced significantly by 66%, 65%, and 78%, respectively, compared with those of E51-D230. The EHEP-D230 residual char exhibited a compact and continuous exterior structure and a honeycomb-like hollow vesicle interior structure. This unique intumescent char endowed EHEP-D230 with excellent flame retardancy and smoke suppression, rendering it a potential candidate for fire-resistant applications.