Microcellular foamed polyamide 6/carbon nanotube composites with superior electromagnetic wave absorption

Electromagnetic (EM) wave pollution causing damage to precision equipment and threatening the health of living organisms has attracted considerable attention. Herein, promising microcellular foamed polyamide 6 (PA6)/carbon nanotube (CNT) composites for highly efficient EM wave absorption were successfully fabricated using supercritical CO2 foaming. Nanocomposites foams with a void fraction ranging from 38.7% to 85.1% were achieved, providing a platform to assess the correlation of the electrical conductivity, the dielectric permittivity and the EM wave absorption properties with porosity. Notably, the Foam-257.5C sample with a void fraction of 38.7% exhibited outstanding EM wave absorption characteristics at a thickness of only 1.59 mm and an ultra-low reflection loss value of -55.3 dB (99.9997% wave absorption). Most importantly, the effective absorption bandwidth (EAB) of the Foam-257.5C sample could cover the entire Ku band (12.4–18 GHz) by slightly adjusting the thickness from 1.20 to 1.60 mm. The superior EM wave absorption performance of the Foam-257.5C sample was attributed to multiple reflections and scattering at the solid-gas interfaces, favorable impedance matching due to the existence of a large polymer-air interface area, conductive loss near the interfaces and interfacial polarization. Thus, this study offers an eco-friendly, simple and versatile methodology to develop high-efficiency, flexible polymer-based EM wave absorbents.