Preparation of Wave Absorbing Coatings Blended Waterborne Polyurethane with Nano Fe3O4/MWCNTs and Their Electromagnetic Absorption Properties

The development of high-performance electromagnetic wave (EMW) absorbing materials aims to achieve high-intensity electromagnetic attenuation and wide effective absorption bandwidth (EAB), but in fact, it is challenging for them to optimize synchronously. In this paper, through the hydrothermal method, an EMW absorber was synthesized by loading nanomagnetic Fe3O4 on multi walled carbon nanotubes (MWCNTs), of which the structure and properties depend on precursor (FeCl3·6H2O) addition and MWCNTs modification. Using this absorber, a coating named Fe3O4/MWCNTs/WPU with good EMW absorption performance was prepared with waterborne polyurethane (WPU). By characterizing the structure and properties of the absorbers and coatings, it was found that the optimal distribution of Fe3O4 particles presented when adding 1.0 g FeCl3·6H2O. After MWCNTs acidizing modification, Fe3O4 particles present on them with a “bead-chain” like uniformly dense structure, and the coating exhibited a wider EAB of 8.64 GHz at a thickness of 3.0 mm and a smaller reflection loss of −52.61 dB at a thickness of 4.0 mm. These findings effectively achieve the balance between EAB and intensity of EMW, and reveal some principles for optimizing electromagnetic absorption, providing important basis for designing new materials with wide bandwidth and strong absorption capacity.