Phosphorus-Free Ellagic Acid-Derived Epoxy Thermosets with Intrinsic Antiflammability and High Glass Transition Temperature

Because fossil-based resources are constantly declining, it has become a crucial issue in both academic and industrial fields to develop biobased polymers from renewable resources. Despite excellent comprehensive properties, diglycidyl ether of bisphenol A (DGEBA)-type epoxy resin suffers from nonrenewability and flammability. To overcome these shortcomings, a biobased epoxy monomer (DGEEA) derived from ellagic acid (EA) was successfully synthesized and well characterized in this study. The DGEEA monomer was cured by 4,4′-diaminodiphenylmethane (DDM) to obtain a biobased epoxy thermoset, with DGEBA cured by DDM as a control sample. The cured DGEEA/DDM product showed a high glass transition temperature of 220 °C, a high tensile strength of 75.8 MPa, and a high Young’s modulus of 2.7 GPa, which outperformed the conventional petroleum-based DGEBA/DDM system. Compared with the cured DGEBA/DDM system, the cured DGEEA/DDM product also exhibited an excellent intrinsic antiflammability in terms of the significantly decreased peak heat release rate (77.7 W/g versus 513.9 W/g) and the notably improved limiting oxygen index (40.0% versus 23.0%). Furthermore, the cured DGEEA/DDM product could self-extinct in the UL-94 vertical burning test (corresponding to the V-0 classification), while the cured DGEBA/DDM system burnt out eventually (no classification). The current study provides a prospective path for synthesizing biobased resin with abundant aromatic structures and makes a contribution to the generation of biobased fire-safe epoxy thermosets with exceptional comprehensive properties.