The effect of filler functionalization on dispersion and thermal conductivity of polypropylene/multi wall carbon nanotubes composites

This paper deals with melt blended polypropylene based nanocomposites filled with multi wall carbon nanotubes. The effect of the content of unfunctionalized, amino- and carboxyl-functionalized carbon nanotubes having the same aspect ratio on their actual dispersion is investigated by dynamic rheological measurements and transmission electron microscopy observations. In particular, the former tests highlight a greater propensity to percolate of non functionalized nanotubes with respect to amino surface modified ones and even the absence of terminal effects in presence of carboxyl functionalized carbon nanotubes. Morphological observations, instead, show dispersion and agglomeration effects typically expected by increasing the carbon nanotubes loading. Moreover, through-plane steady-state evaluations of their thermal conductivity reveal a cubic polynomial trend of this parameter as a function of the filler content. This behaviour is interpreted in terms of the "average inter-aggregate distance (AID)" related to competitive dispersion/agglomeration phenomena to which added multi wall carbon nanotubes are subjected during the preparation of compounds with concentrations over specific threshold values.