Construction of designable and high-temperature resistant composite foams for tunable electromagnetic shielding

Conductive polymer composite (CPC) foams have been extensively studied for electromagnetic interference (EMI) shielding due to their lower density and relatively low EM reflectivity. However, most CPC foams are difficult to structurally design to regulate performance, and also limited in high-temperature application scenarios owing to the low-temperature resistance of the matrix themselves. Herein, high-performance expanded polyetherimide (EPEI) foam beads were fabricated by subcritical foaming technology with organic solvents/CO2 as co-blowing agents, and designable EPEI/CNS (carbon nanostructures) composite foams with segregated networks and high-temperature resistance were then manufactured through CNS dip-coating and epoxy bonding. The resultant EPEI/CNS composite foams showed the shielding effectiveness (SE) of ∼11.9–39.5 dB with CNS loading of only ∼0.25–0.72 vol%, along with R coefficient of only ∼0.26–0.56. The construction of asymmetric gradient structure in the foams via orderly assembling can further reduce the EM reflection in comparison with uniform structure, thereby remitting the secondary EM pollution. Moreover, the EPEI/CNS composite foams can not only maintain the structural integrity after being treated at ∼200 °C, but also maintain relatively stable EMI SE and most of their mechanical properties, enabling their applications in high-temperature environments. This work provides a simple and effective method for constructing high-temperature resistant CPC foams for tunable EMI shielding.