Fabrication of flexible waterborne polyurethane/Fe-doped residual carbon from coal hydrogasification semi-coke composites for high-performance microwave absorption

A series of microwave absorbers (SFs) were prepared using coal hydrogasification semi-coke as the carbon and ferric nitrate as the magnetic precursors. The absorbers were then incorporated to waterborne polyurethane to prepare composites (WSF). The microwave absorption performance of the composites can be tuned by adjusting the annealing temperature of the hybrids. The composite films can be fabricated to gradient or homogeneous structures by a facile viscosity-controlling method. The film with gradient structure is more conducive to alleviating the impedance mismatch and enhancing the attenuation. The WSF700 composite with gradient structure performs favorable MA property, with the minimum reflection loss of −42.08 dB and effective absorption bandwidth of 6.78 GHz at a thickness of 1.7 mm. The preparation strategy is rather facile, and the ingredients are inexpensive and easily accessible. This work shows great potential for the applications of the composites in MA coatings and flexible electronics.