Several polymers were modified with multiwalled carbon nanotubes (CNT) to study the influences of the crystallization in the polymeric matrix and of the CNT orientation during extrusion on the electrical conductivity. Experiments were carried out with common semi-crystalline polymers (polypropylene, polyethylene, polyamide 6) and compared to an amorphous polymer (ethylene vinyl acetate). All polymers were grades with low viscosity, so that the CNT could be oriented well during extrusion. For all materials, the percolation threshold was determined, and the lowest value of 3% was found in polypropylene. The percolation threshold was correlated to the degree of crystallinity of the matrix polymers, so that crystallites could be seen as an excluded volume for CNT. The crystallization itself was analyzed by differential scanning calorimetry (DSC), whereby nucleation effects and changes in the crystallization temperature were found. The shear rate during extrusion had a large influence on the electrical conductivity. This effect was analyzed by transmission electron microscopy (TEM), with which the orientation of CNT in the direction of extrusion was visualized and differences between the polymer matrices were explained.
The orientation behavior of well-dispersed multiwalled carbon nanotubes (CNTs) within high-speed melt-spun semicrystalline polymer fibers has for the first time been studied using three-dimensional reconstructions from bright-field transmission electron microscopy (TEM) tomography. The local investigation technique allows separating contributions stemming from additionally present CNT aggregates. Over a relatively narrow draw ratio range applied during the fiber production process, a transition region is found, in which the CNTs change their orientation from being aligned perpendicular to being aligned parallel to the fiber axis. Complementary performed wide-angle X-ray scattering measurements and mechanical analysis of the polymer/CNT nanocomposite fibers reveal a strong correlation between the CNT orientation and the structural and mechanical properties of the fibers. Characteristic quantities such as crystallinity, crystal size, and correlation length parameters of crystalline and amorphous polymer chains undergo significant changes within the CNT orientation transition region indicative of a cooperative process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.