Structure design of multi-layered ABS/CNTs composite foams for EMI shielding application with low reflection and high absorption characteristics

The low-reflection and high-absorption features for electromagnetic (EM) waves are the key and significant requirements for fabricating efficient EM interference (EMI) shielding polymer-based composite foams. Herein, single-layered acrylonitrile–butadienestyrene (ABS)/carbon nanotubes (CNTs) foams with three representative pore structures (nano-pores, micro-pores and regular pores) were produced via supercritical CO2 foaming technology. Subsequently, they were stacked together to obtain multi-layered ABS/CNTs foams through structural design for achieving the high absorption and low reflection characteristics described above. Among all the unfoamed and foamed ABS/CNTs specimens, nano-porous ABS/CNTs foams could reach the maximum electrical conductivity of 3.7 S/m. The multi-layered ABS/CNTs foam with positive pore gradient structure exhibited the best EM wave absorption coefficient of 0.90. The sandwich structure formed in ABS/CNTs foam by sandwiching a middle layer of regular porous foam between nano-porous foam and micro-porous foam increased EM wave absorption properties, owing to the generation of constructive interference. This work provides new insight and methodology for the design and fabrication of multi-layered EMI shielding polymer-based composite foams with low reflection and high absorption.