Asymmetric‐Structured Waterborne Polyurethane Foams for Enhanced Electromagnetic Wave Absorption Performance

In this work, expanded graphite (EG) and nickel‐coated graphite (Ni@G) are used to prepare asymmetric electromagnetic wave‐absorbing materials based on waterborne polyurethane (WPU). In the process of preparation, thermally expanded microspheres (TEMs) foams in situ to form closed foam cells. The density of EG is close to that of WPU and is uniformly dispersed in the whole composite. Ni@G is dense and deposited at the bottom of the material under gravity, providing magnetic loss. When the content of TEMs reaches 2 wt%, the density of the foam is less than 1, and the foam with the best absorbing capacity can be obtained. when its thickness is 2 mm, it has the minimum reflection loss of −69.9 dB and the effective absorption bandwidth of 5.04 GHz. In this article, a lightweight and efficient electromagnetic wave (EMW) absorption foam is prepared, which provides some ideas for EMW absorption.