The influence of gradient and sandwich configurations on the electromagnetic interference shielding performance of multilayered thermoplastic polyurethane/graphene composite foams

Multilayered thermoplastic polyurethane/graphene (PUG) composites were fabricated by stacking single-layered PUG foams together. The arrangement of single-layered PUG foams in different orders could realize the gradient concentration of graphene, which was proved to be a facile approach to enhance the microwave-absorbing (MA) property of PUG composites, rather than their electromagnetic interference (EMI) shielding effectiveness (SE). Further sandwiching a wave-transmitting layer between two pieces of PUG foams formed a sandwich structure, by which the SE of the two samples could be significantly improved and the resultant composites still possessed strong MA performance. The SE increment was assigned to the enhanced reflection loss induced by constructive interference, and largely dependent on the thickness of the interlayer d. Particularly, when the values of the d were zero and the quarter of the largest wavelength in the testing frequency range, the minimum and maximum SE could be obtained, respectively. These results are critical to the fabrication of high-performance polymer-based shielding materials with strong MA property.