Adding conductive carbon fillers to insulating thermoplastic polymers increases the resulting composite's electrical conductivity. Carbon nanotubes (CNTs) are very effective at increasing composite electrical conductivity at low loading levels without compromising composite tensile and flexural properties. In this study, varying amounts (2-8 wt %) of CNTs were added to polycarbonate (PC) by melt compounding, and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile and flexural properties. The percolation threshold was less than 1.4 vol % CNT, likely because of CNTs high aspect ratio (1000). The addition of CNT to PC increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 6 wt % (4.2 vol %) CNT in PC resin had a good combination of properties for electrical conductivity applications. The electrical resistivity and thermal conductivity were 18 X-cm and 0.28 W/m Á K, respectively. The tensile modulus, ultimate tensile strength (UTS), and strain at UTS were 2.7 GPa, 56 MPa, and 2.8%, respectively. The flexural modulus, ultimate flexural strength, and strain at ultimate flexural strength were 3.6 GPa, 125 MPa, and 5.5%, respectively. Ductile tensile behavior is noted in pure PC and in samples containing up to 6 wt % CNT.
A potential application for conductive resins is in bipolar plates for use in fuel cells. The addition of carbon filler can increase the electrical and thermal conductivities of the polymer matrix but will also have an effect on the tensile and flexural properties, important for bipolar plates. In this research, three different types of carbon (carbon black, synthetic graphite, and carbon nanotubes) were added to polypropylene and the effects of these single fillers on the flexural and tensile properties were measured. All three carbon fillers caused an increase in the tensile and flexural modulus of the composite. The ultimate tensile and flexural strengths decreased with the addition of carbon black and synthetic graphite, but increased for carbon nanotubes/polypropylene composites due to the difference in the aspect ratio of this filler compared to carbon black and synthetic graphite. Finally, it was found that the Nielsen model gave the best prediction of the tensile modulus for the polypropylene based composites.
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