Percolation and gel-like behavior of multiwalled carbon nanotube/polypropylene composites influenced by nanotube aspect ratio

The influence of aspect ratio of multiwalled carbon nanotube (MWCNTs) on rheological and electrical properties of MWCNT/polypropylene (PP) composites has been studied. Owing to the pre-grinding for MWCNTs and the efficient twin-extruder mixing, the dispersion of MWCNTs of different aspect ratios in the PP matrix is all uniform and homogeneous. With incorporation of 10 wt% MWCNTs with an aspect ratio of 167, an electrical conductivity of 1.2 S/cm could be achieved. A concept of “gel-like behavior” is introduced to investigate the MWCNT network formation within the composites. The rheological percolation threshold (cpG') and the gel content (cg) of different MWCNT/PP composites are derived by applying the power law scaling and the Winter-Chambon method, respectively. It is revealed that the composites containing MWCNTs with the largest aspect ratio have the lowest cpG' and cg values. Furthermore, the electrical conductivities of composites are measured and the electrical percolation thresholds (cpσ) are obtained. The difference in gel content among different aspect ratios as well as the difference between rheological and electrical percolation thresholds is discussed.