Abstract
Differential scanning calorimetry (DSC), X-ray diffraction, dynamic mechanical analysis (DMA) and electrical conductivity measurements were performed on multiwalled carbon nanotube/polyamide 6,6 composites with four different types of well-characterized tubes manufactured using fixed-bed catalytic processes. The tubes differed in diameter, number of walls and surface chemistry. Except for one very poorly formed set of tubes, there were not large differences in behavior with respect to modulus, maximum electrical conductivity and percolation threshold; none of which differed by more than a factor of 2 for the three types of tubes. However, the shape of the percolation region was very different for the larger diameter tubes in that the percolation region occurred over a much wider concentration. Glass transition and crystallization/melting characteristics also showed very small differences between the three types of tubes. One unique observation made in this work was that the glass transition temperature (Tg) showed a qualitatively different behavior depending on what was used to measure the transition: DSC indicated an increase in Tg with added nanotubes while DMA showed a decrease in Tg. Other than the difference being related to how the Tg was measured, it is not clear what caused the qualitatively different behavior.
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