Double percolated MWCNTs loaded PC/SAN nanocomposites as an absorbing electromagnetic shield

This research reports on the preparation and characterization of absorbing electromagnetic (EM) nanocomposite shields based on polycarbonate (PC)/polystyrene-co-acrylonitrile (SAN) 60/40 blend containing low contents of multi-walled carbon nanotubes (MWCNTs). The nanocomposites were prepared using a melt-compounding process at a temperature of 260 degrees C. The melt linear viscoelastic results together with scanning electron microscopy (SEM) micrographs implied a co-continuous type morphology, which remained unchanged by the addition of nanoparticles (NPs). The results of dynamic mechanical thermal analysis (DMTA) suggested a preferential localization of MWCNTs in the PC phase, evidenced by the transmission electron microscopy (TEM) micrograph. The direct current (DC) electrical conductivity results showed a low electrical double percolation threshold around 0.32 wt% of MWCNTs. A maximum DC electrical conductivity of 0.0834 S/cm was obtained for 1 wt% MWCNTs-filled nanocomposite. Applying EM theory based on the measured dielectric permittivity and magnetic permeability [over the X-band frequency (8.2-12.4 GHz)] suggested a maximum shielding efficiency of 25-29 dB for the 1 wt% MWCNTs-filled nanocomposite with a thickness of 10 mm. In addition, the contribution of the absorption mechanism below and above the electrical percolation threshold was studied. It was revealed that the shielding performance of the nanocomposites is mainly due to noticeable absorption of EM waves above the percolation threshold, which was attributed to the induced conductance loss as a result of the formation of conductive paths.