Constructing 3D expanded graphite-silver segregated network structure for ultra-efficient EMI shielding and low reflection

Abstract

Lightweight, flexible and high-performance (high efficiency and low reflection) electromagnetic interference (EMI) shielding materials are urgently needed to cope with the increasingly complex electromagnetic (EM) radiation environment. In this study, the thermoplastic polyurethane/expanded graphite/silver (TPU/EG/Ag) composite foams with three-dimensional (3D) isolated conductive network were successfully manufactured through the combination of supercritical carbon dioxide (scCO2) foaming and chemical deposition. This composite foam achieves a conductivity up to 171.2 S/m and an EMI SE of 56.3 dB with only 0.58 vol% Ag on account of the volume exclusion of pores and the selective enrichment of Ag nanoparticles. The weight reduction rate of the composite exceeds 74%, and the density of the foamed sample can be as low as 0.21 g/cm3 by introducing a porous structure. Interestingly, the presence of porosity also alleviates impedance mismatch between the composites and air, and the reflectivity of composite is reduced from 99% to 31% owing to the multiple absorption in porous structure, which significantly weakens the serious secondary EM radiation pollution. Moreover, benefiting from the secondary melting at the interface of the TPU isolation unit, these composite foams exhibit favorable compressible recovery performance and shielding stability after 50 cycles of compression. This work proposes a new idea for the lightweight and flexible design of EMI shielding composites, opening a new path for the development of next-generation absorption-based EMI shielding materials.