Shielding effectiveness of carbon-filled polypropylene composites

Adding conductive carbon fillers to insulating thermoplastic resins increases composite shielding effectiveness. In this study, varying amounts of three different carbons (carbon black, synthetic graphite particles, and carbon nanotubes) were added to polypropylene resin. The resulting single filler composites were tested for shielding effectiveness. The effects of single fillers and combinations of two different carbon fillers were studied via a factorial design. At the highest single filler loadings, the following shielding effectiveness results were obtained at 800 MHz: 23.4 dB for 10 wt% carbon black/polypropylene, 34.7 dB for 70 wt% synthetic graphite/polypropylene, and 45.9 dB for 15 wt% carbon nanotubes/polypropylene. The factorial results indicated that for the composites containing only single fillers, carbon nanotubes, carbon black, and synthetic graphite cause a statistically significant increase in composite shielding effectiveness. All composites containing combinations of two different fillers had a statistically significant effect which increased shielding effectiveness. The shielding effectiveness values for the 2.5 wt% carbon black/65 wt% synthetic graphite/polypropylene and 65 wt% synthetic graphite/6 wt% carbon nanotubes/polypropylene composites are >60 dB, which is higher than that of many metals.