Fe3O4@CNTs/WPU@CNF aerogel/Ag foam composites with a double-layer structure for absorption-dominated electromagnetic shielding performance

Abstract

With the popularity of electronic devices, absorption-dominated multilayered electromagnetic shielding materials are increasingly attractive due to the effective decrease of second pollution compared to the traditional homogeneous electromagnetic shielding materials. However, the design of multilayered structure and strong interface adhesion of functional composite while keeping light weight and practical use is not readily to realize. Therefore, we propose herein a double-layer aerogel/foam composite electromagnetic shielding composite. The absorption layer is made by a nanocellulose (CNF)@waterborne polyurethane (WPU) aerogel, in which magnetic nano iron tetraoxide (Fe3O4) joined with carbon nanotubes (CNTs) to optimize the impedance matching. The reflection layer is a chemically silver-plated foam (AF) used to reflect the transmitted electromagnetic waves through its strong electrical conductivity, improving the overall ability of electromagnetic waves shielding and achieving enhanced electromagnetic shielding performance. The two layers are strongly combined by the adhesion of WPU without the use of adhesives. When the mass ratio of CNTs to Fe3O4 of 2:1 and the total mass fraction of 5 wt%, the EMI shielding efficiency of the composites reaches 62.81 dB in the X-band (8.2–12.4 GHz) at the thickness of 4 mm and the maximum value reaches a remarkable 76.63 dB at 1.17 GHz. The specific SE value of SSE/t reaches 1744.72 dB cm2 g−1. Thanks to the effect of AF layer, the average reflectivity is only 0.141, demonstrating an absorption-dominated shielding mechanism. In addition, the as-prepared composite material is remarkably flexible and deformation-resistant, with a density of only 0.0913 g cm−3 and can withstand approximately 85,000 times its own weight.