Rheology, crystallization behavior, and dielectric study on molecular dynamics of polypropylene composites with multi-walled carbon nanotubes and clay

The study is focused on joint effects of two nanofillers in polypropylene (PP) reinforced with 3 wt% organo-clay (?C) and 0.1-5 wt% multi-wall carbon nanotubes (MWCNTs). The composites were produced by extrusion and characterized by rheology, differential scanning calorimeter (DSC), thermally stimulated depolarization currents (TSDC), and dielectric relaxation spectroscopy (DRS). Rheological data indicates ? formation of a network structure related to percolation above 1 wt% nanotubes. The flow activation energy (Ea) decreases above the percolation threshold, thus, the presence of clay improves the debundling of MWCNTs and releases the segmental motion of polymer chains. The clay does not affect the crystallization behavior of PP, but the nucleation is enhanced strongly by the MWCNTs. Dielectric measurements reveal that the presence of clay affects the molecular mobility of PP at the amorphous phase. The DSC results imply that around 80°C a cold crystallization process occur in the PP phase which has a significant impact on the dielectric segmental relaxation process and gives rise to the appearance of an additional process, the so called "interfacial" relaxation process. This new relaxation process in the three-phase composites was attributed to an interfacial polarization process due to blocking of charge carriers at polymer/clay interfaces