In this study, the concept of double percolation and selective location of a conducting additive was used to develop conducting polymer composites composed of polystyrene (PS) and ethylene vinyl acetate copolymer (EVA) filled with carbon black (CB). Scanning and transmission electron microscopy suggested that the CB was preferentially located in the EVA phase. By combining a cocontinuous morphology and selective location of CB in the EVA phase, we achieved the highest conductivity values and better electromagnetic interference shielding effectiveness in the X-band frequency range for the 70:30 w/w PS/EVA blend. Electromagnetic attenuation occurred by both reflection and absorption mechanisms, although the first was predominant for composites with a higher amount of CB. The percolation thresholds of the PS, EVA, and 70:30 w/w PS/EVA blend loaded with CB were estimated from the dependence of the alternating-current and direct-current conductivities. The rheological properties were also used to relate the electrical behavior to the microstructure of the composites.
Partially bio‐based conducting polymer nanocomposites constituted by poly(lactic acid) (PLA)/ethylene‐co‐vinyl acetate (EVA) (50:50 wt%) blend loaded with different amounts of carbon nanotube (CNT) were prepared for developing microwave absorbing materials. The effect of EVA characteristics and the mixing conditions on the electrical conductivity was investigated. The higher conductivity value was achieved using PLA@CNT master batch and EVA with 28% of VA. In fact, this system presented electrical percolation threshold of 7 × 10−4 volume fraction and a conductivity value of 3 × 10−3 S/m with the addition of 0.9 wt% (0.58 vol%) of CNT. A minimum reflection loss of −29 dB (electromagnetic (EM) attenuation of around 99.9%) at 11.7 GHz and the bandwidth (<−10 dB) of 4.9 GHz was observed with the presence of 0.58 vol% of CNT, whereas RL value of around −39.4 dB (EM attenuation of around 99.99%) at 14.7 GHz and a bandwidth of 4.6 GHz was observed for the composite loaded with 0.25 vol% of CNT. Due to the outstanding microwave absorption properties and wide absorption bandwidth with low amount of CNT, these composites are promising candidates for flexible materials suitable for shielding electronic devices in a wide frequency range.
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