Fabrication of lightweight flexible thermoplastic polyurethane/multiwalled carbon nanotubes composite foams for adjustable frequency-selective electromagnetic interference shielding by supercritical carbon dioxide

In this study, the thermoplastic polyurethane (TPU)/multiwalled carbon nanotubes (MWCNTs) lightweight flexible foam with sandwich structure was achieved by supercritical carbon dioxide (scCO 2 ) foaming. This work studied the relationship between foaming behavior and electromagnetic interference (EMI) shielding performance. The results showed that the formation of cell structure could not only achieve the purpose of lightweight, but also control the position of electromagnetic interference shielding efficiency (EMI SE) peak by adjusting foaming temperatures. The EMI SE peak could shift to high frequencies as the foaming temperature increases, and the adjustable frequency ranged from 9.76 GHz to 14.72 GHz. The maximum EMI SE of TPU/MWCNTs composite foams increased to 44.86 dB under 2.5 wt% filler content with a density of 0.61 g/cm 3 . This work provided a feasible idea for the preparation of lightweight and adjustable frequency-selective EMI shielding composite materials by supercritical fluid foaming. • Frequency-selective EMI shielding TPU/MWCNTs foams were prepared by scCO 2 . • EMI SE peak position could be controlled by adjusting foaming ratios. • Surface is conductive while direction of EMI shielding is insulated. • EMI SE of TPU/MWCNTs composites with sandwich structure increases after foaming.