All-in-One Epoxy Composites Modified with Biobased Microspheres for Simultaneously Enhancing Flame Retardancy, Toughness, and Dielectricity

Epoxy resins (EP) have been commonly used as versatile matrixes for high-performance composites. However, the inherent high flammability of EP resin poses significant fire hazards. Moreover, it is challenging to simultaneously meet the stringent requirements of high-temperature mechanical stability and high-frequency dielectric properties for application in the electronics industry and aerospace field. To address these limitations, we propose a synergistic strategy of “Molecular Functionalization-Microsphere Engineering”: a biobased furfuryl alcohol-derived DOPO flame-retardant monomer (FA-DOPO) was specially designed and synthesized. Subsequently, FA-DOPO was copolymerized with maleic anhydride to prepare monodisperse and size-controllable flame-retardant microspheres (DFDMs) via self-stabilized precipitation polymerization. DFDMs can serve as a highly efficient flame retardant through a synergistic mechanism involving the formation of a physical barrier via FA-derived charring and radical quenching by DOPO. Therefore, the modified EP/DFDM composites achieved exceptional flame retardancy (LOI = 32.7) at an ultralow DFDM loading of 5 wt %. Remarkably, the EP/DFDM composites simultaneously exhibited a 103% enhancement in impact strength and an extremely low dielectric constant of 3.0 at 107 Hz. Considering the highly enhanced comprehensive properties, the EP/DFDM composites in our present work possess great potential for safety-critical applications, such as aerospace components, printed circuit boards, and advanced electronic packaging for 5G and high-frequency devices.