Facile and Green Method To Structure Ultralow-Threshold and Lightweight Polystyrene/MWCNT Composites with Segregated Conductive Networks for Efficient Electromagnetic Interference Shielding

Porous conductive polymer composites (CPCs) with lower density and high performance are more favorable for practical electromagnetic interference (EMI) shielding application. In this work, a judicious combination of high-speed mechanical mixing and supercritical carbon dioxide (scCO2) foaming was applied to prepare lightweight polystyrene (PS)/multiwall carbon nanotube (MWCNT) composites with segregated conductive networks. The composite foam presented an ultralow percolation threshold of 0.07 vol % and exhibited excellent electrical conductivity of 8.05 S/m and EMI shielding effectiveness of 23.2 dB, exceeding the requirement of EMI shielding materials in commercial application, with density of 0.47 g/cm3 at such a low thickness of 1.8 mm and 1.88 vol % MWCNT loading. In addition, the EMI shielding mechanism was further clarified and the results showed that absorption was the primary EMI shielding mechanism for such conductive porous composites in the frequency range of 8.2–12.4 GHz. Meanwhile, the effect of foaming on the EMI shielding mechanism was also investigated. Results indicated that the electromagnetic absorption was increased from 90.5% to 95.9% at the same MWCNT content of 7 wt %. Consequently, this material with high performance and its facile, versatile, green fabrication method provide a novel idea for preparing lightweight EMI shielding materials.