Microcellular epoxy/graphene nanocomposites with outstanding electromagnetic interference shielding and mechanical performance by overcoming nanofiller loading/dispersion dichotomy

With the rapid evolvement of wireless communication technologies, the ever increasing needs to prevent electromagnetic waves (EMWs) pollution have urged the development of lightweight materials with excellent electromagnetic interference (EMI) shielding property. However, achieving desired EMI shielding performance often requires high loadings of conductive nanofillers, like graphene, which poses challenges to control the nanoparticle dispersion and the mechanical performance of the nanocomposite. Herein, we demonstrate a method to fabricate highly-loaded (>30 wt%) graphene in microcellular epoxy nanocomposites, successfully overcoming the long-lasting dichotomy in the field of nanocomposites of high filler loading and dispersion. By utilizing supercritical CO₂ foaming method, modified thermosetting epoxy-based nanocomposite was foamed with multiple interfaces and tunable microcellular cells. In addition, a rearrangement of nanofillers during foaming process is favorable for more intense conductive network, leading to enhanced EMWs attenuation by repeated reflections and absorptions. An optimal combination of electrical conductivity (314 S m⁻¹), EMI shielding effectiveness (86.6 dB and 156.3 dB/(g/cm³)), compressive strength (27.4 MPa) and density (0.55 g cm⁻³) has been achieved for foamed nanocomposite with 32.26 wt % graphene content. This versatile method opens up an easy route to fabricate lightweight structural foams with high nanofiller contents, which could be used in many applications such as electronics, robotics, and aircrafts.