Multiple layered PVDF-CNTs foams with gradient structure and high electromagnetic shielding performance

Multiple layered PVDF-CNTs with different CNTs were prepared by facile melt blending process. Due to varied electrical conductivity in each layer, incident electromagnetic (EM) waves could be reflected and absorbed between these layers, and thus their electromagnetic interference (EMI) efficiency was obviously improved. EMI shielding effectiveness of a three- layered PVDF-CNTs with CNTs content of 6, 8, 10 wt. % sequentially, is 36.4 dB, compared to a 27.2 dB of single layered PVDF-8CNTs with a same sample thickness of 2 mm, an increase of 34% was induced. Furthermore, based on different viscoelasticity of PVDF-CNTs with various CNTs content, three- layered PVDF-6–8-10 CNTs foams with a gradient cell structure and thickness of 2 mm, were manufactured by an environment friendly supercritical CO₂ batch foaming method, an absolute EM SE value of 35.2 dB at a frequency of 26 GHz was measured. Because of the introduction of microcellular sized cells, the electromagnetic waves were absorbed and reflected inside the cells, cooperated with the multiple reflections between different layers, an increased absorption dominated mechanism in these foamed PVDF-CNTs composites was resulted, which means a successful mechanism transformation from reflection to absorption after foaming.