Microcellular foamed bilayer iPP/CNTs-HDPE/CNTs nanocomposites for electromagnetic interference shielding application

The increasing electromagnetic (EM) radiation pollution necessitates the development of low-cost, lightweight, and high absorption-dominated electromagnetic interference (EMI) shielding composites. Herein, the isotactic polypropylene (iPP)/high-density polyethylene (HDPE)/carbon nanotubes (CNTs) nanocomposite foams were fabricated using a simple melt blending method, followed by an eco-friendly foaming process with supercritical CO₂ as the blowing agent. The asymmetric bilayer structure of resulting iPP/HDPE/CNTs nanocomposite foams was produced by integrating iPP/CNTs and HDPE/CNTs segments, followed by a foaming process. Due to the different melt strength and viscoelasticity of iPP and HDPE, this asymmetric bilayer nanocomposite foams with identical CNTs content exhibited diverse structures and unique EMI shielding properties. Specifically, the HDPE/CNTs layer served as an absorption layer due to its relatively low electrical conductivity, whereas iPP/CNTs layer functioned as a reflective layer owing to its high electrical conductivity, leading to the formation of a distinct absorption-reflection-reabsorption interface within the iPP/HDPE/CNTs nanocomposite foams. Finally, the unique asymmetric structure endowed the nanocomposite foams with superior EMI shielding effectiveness of 37.32 dB, as well as a high absorption coefficient of 0.60, rendering the nanocomposite foams absorption-dominated EMI shielding materials and effectively preventing secondary EM wave pollution.