Carbon nanotube/isotactic polypropylene composites prepared by latex technology: Morphology analysis of CNT-induced nucleation

The crystallization behavior of isotactic polypropylene (iPP) in the vicinity of single-wall and multiwall carbon nanotubes (SWCNTs and MWCNTs) has been studied. Combined DSC and transmission electron microscopy (TEM) investigations of bulk composite materials reveal that CNTs nucleate iPP when crystallizing from the quiescent melt and that iPP crystals form a transcrystalline layer of aligned iPP lamellar crystals around the nucleating CNT. The pronounced nucleation effect and the formation of a transcrystalline layer is observed also for ultrathin film CNT/iPP samples. Corresponding diffraction studies show that in bulk as well as in the case of the ultrathin film samples only the ?-phase of iPP exists. The transcrystalline layer is highly oriented around the nucleating CNTs, and the crystallographic c-axes of the lamellae are oriented perpendicular to the long axis of the nucleating CNT, which is in contradiction to assumptions done in other studies. This crystallization behavior is discussed and a possible explanation is provided based on iPP macromolecules wrapped around rather than aligned along the CNTs prior to formation of the nucleus. © 2008 American Chemical Society