Influence of conductive nano- and microfiller distribution on electrical conductivity and EMI shielding properties of polymer/carbon composites

In this work, DC conductivity and EMI shielding characteristics in the frequency range of 25.5–37.5 GHz (Ka-band) of polymer composites based on ultrahigh-molecular-weight polyethylene (PE) and polypropylene (PP) containing different types of nano- and microfillers were studied. Graphene nanoplatelets (Gr), thermally exfoliated graphite (TEG), thermally treated anthracite (A) and dispersed metals such as iron (Fe) and copper (Cu) were used as conductive fillers. Two types of composites were formed: 1 – with ordered distribution of the filler particles in the form of conductive 3D network in polymer matrix (segregated structure), 2 – with random distribution of the filler particles. It was found that the percolation threshold for Gr and A filler is 100 and 10 times lower in the segregated system was 100 and 10 times lower than that for A filler with its random distribution in polymer matrix. Distinctly increased value of shielding efficiency (SET) in the segregated system can be explained by multiple internal reflection of electromagnetic wave in the network formed in the segregated structure. It was also found that the value of SE corresponds with the electrical conductivity of composites. However, for the same conductivity, higher values of SE were observed for the formed segregated structure in comparison with the literature data for composites with random filler distribution.