Selective Microwave Sintering to Prepare Multifunctional Poly(ether imide) Bead Foams Based on Segregated Carbon Nanotube Conductive Network

Carbon nanotube/poly(ether imide) (CNT/PEI) bead foam parts featuring a lightweight and segregated conductive network were prepared by a judicious combination of selective microwave (MW) sintering and carbon dioxide/tetrahydrofuran (CO2/THF) co-foaming. This way endowed the CNT/PEI conductive foam with adjustable cellular structure and tunable performance by simply changing the CNT content and MW processing condition. Owing to its unique structure, the CNT/PEI conductive foam (0.28 g/cm3) with a CNT content of 0.90 vol % presented a good electrical conductivity (20.7 S/m) and electromagnetic interference (EMI) shielding performance (30.3 dB). In addition, the CNT/PEI conductive foam exhibited an ultralow percolation threshold (0.029 vol %) and presented superior piezoresistive performance under an applied pressure of 0–3.5 MPa and strain of 0–10%, due to the "condensation–recovery" transition mechanism of the integral CNT network of the conductive foam. This study provided an innovative approach to fabricate high-performance polymer bead foam parts with multifunctionality.