Tunable electromagnetic interference shielding performance of polypropylene/carbon black composites via introducing microcellular structure

Abstract

The introduction of cell structures in conductive polymer composites (CPCs) has considerable impacts on electromagnetic interference (EMI) shielding performance of the final CPC foams, and thus it is necessary to clarify the effects of cell structures on the shielding effectiveness (SE) and mechanisms of CPC foams with different filler loadings and expansion ratios more systematically. Herein, polypropylene (PP)/carbon black (CB) composite foams were prepared by core-back foam injection molding (FIM), and their cell structures were well-controlled by changing the CB content and expansion ratio. The results showed that, at different CB contents, the surface EM reflection of all PP/CB foams decreased with increasing the expansion ratio, while their SE values exhibited different trends possibly owing to the changes of sample thickness as well as internal multiple EM reflections/scattering, interfacial polarization and conductive loss during EMI shielding. The EMI SE declined with the increase of expansion ratio for the PP/CB foam with low CB content of 10 wt%, but it was improved for the foam with high CB content of 30 wt%. At a middle CB content of 22.5 wt%, however, the EMI SE of the PP/CB foam first decreased and then increased with the increase of expansion ratio. Our study provides an efficient method to tune the EMI-shielding properties of CPC foams without changing the material weight.