Fabrication of Flexible Thermoplastic Polyurethane/Coal Hydrogasification Semi-coke Composites with Low rGO Content for High-Performance Microwave Absorption

Semi-coke (SC), a residue of coal hydrogasification, is recycled and incorporated into thermoplastic polyurethane (TPU) to create composites for microwave absorption (MA). Herein, we developed porous reduced SC (rSC)-reduced graphene oxide (rGO) hybrids (SGHs) via in situ reduction of a preoxidized SC (oSC) and graphene oxide (GO) mixture. Low-content GO was introduced to considerably improve the dielectric properties of SGHs while decreasing the production cost. Then, a solution blending technique was applied to develop microwave absorbers using TPU as the matrix. The obtained TPU/SGH5 composite with a feed ratio of 5:1 (oSC:GO) showed an optimum reflection loss of -48.81 dB at a thickness of 2.5 mm and an effective absorption bandwidth of 4.30 GHz (7.74-12.04 GHz) in 2-18 GHz. However, the MA property of the obtained composites with the same amount of rSC or rGO alone was not comparable to that of the TPU/SGH5 composite. The inherent magnetism, heteroatoms, and abundance of heterogeneous surfaces of rSC and the considerable dielectric loss of rGO worked together to improve the MA performance of TPU/SGH composites. This study offers an easy and effective technical method for producing high-performance microwave absorbers with a low rGO content, illuminating the path toward achieving sustainable development by converting waste into wealth.