Intrinsically Anti-Flammable Apigenin-derived Epoxy Thermosets with High Glass Transition Temperature and Mechanical Strength

In this work, apigenin was chosen as a raw material to synthesize a novel epoxy monomer (DGEA), while the bio-based epoxy resin was further obtained after curing with 4,4 '-diaminodiphenylmethane (DDM). The control samples were prepared by curing diglycidyl ether of bisphenol A (DGEBA) with DDM. The non-isothermal differential scanning calorimeter (DSC) method was utilized to further investigate the curing behavior and curing kinetics of the DGEA/DDM system. Despite no flame retardant active elements, the DGEA/DDM thermoset still exhibited exceptional anti-flammability. Specifically, the DGEA/DDM thermoset reached a V-0 rating in the UL-94 test and owned a high limiting oxygen index (LOI) value of 37.0%, while DGEBA/DDM resins were consumed completely in the vertical combustion test with a low LOI of 23.0%. Furthermore, the microscale combustion calorimetry (MCC) results manifested that compared with DGEBA/DDM resins, both PHRR and THR values of the DGEA/DDM resins were dropped by 84.0% and 57.6%, respectively. Additionally, the DGEA/DDM resin also presented higher storage modulus and tensile strength compared with DGEBA/DDM one. Particularly, in contrast with that of the cured DGEBA/DDM one (156 degrees C), the DGEA/DDM thermoset displayed an extremely high glass transition temperature (232 degrees C). This study breaks new ground on how to produce bio-based monomers with aromatic structures and achieve high-performance thermosetting polymers.