A specific alignment and distribution of rod-like fillers inside a polymer matrix is pivotal in order to enhance the particular properties of the filled material in certain directions. The present work explores the conditions of multiwall carbon nanotubes (MWCNTs) inside different polymer multilayer systems during forced assembly coextrusion. One system was composed of alternated layers of linear low-density polyethylene (LLDPE) and LLDPE filled with MWCNTs (LLDPECNT). The other system was composed of alternated layers of a linear polypropylene filled with MWCNTs (PPCCNT) and a long-chain branched polypropylene (PPH). Interestingly, for the PPCCNT/PPH multilayer systems, when the number of layers increased to a certain amount, the layer thickness decreased close to or below the average length of the MWCNTs thus causing an enhanced MWCNT orientation parallel to the layer direction as well as the flow direction. Conversely, the same phenomenon was not observed for the LLDPECNT multilayer systems. The enhancement of the MWCNT orientation in the PP system was explained by the more effective layer confinement of PPH layers to the PPCCNT layers. The MWCNT conditions inside different polymers was then further reflected by characterization of the microstructures and electrical behaviors.
Li et al. (Wed,) studied this question.