Low percolation threshold in single-walled carbon nanotube/high density polyethylene composites prepared by melt processing technique

A new method was developed to disperse carbon nanotubes (CNTs) in a matrix polymer and then to prepare composites by melt processing technique. Due to high surface energy and strong adsorptive states of nano-materials, single-walled carbon nanotubes (SWNTs) were adsorbed onto the surface of polymer powders by spraying SWNT aqueous suspected solution onto fine high density polyethylene (HDPE) powders. The dried SWNTs/powders were blended in a twin-screw mixture, and the resulting composites exhibited a uniformly dispersion of SWNTs in the matrix polymer. The electrical conductivity and the rheological behavior of these composites were investigated. At low frequencies, complex viscosities become almost independent of the frequency as nanotubes loading being more than 1.5 wt%, suggesting an onset of solid-like behavior and hence a rheological percolation threshold at the loading level. However, the electrical percolation threshold is ∼4 wt% of nanotube loading. This difference in the percolation thresholds is understood in terms of the smaller nanotube-nanotube distance required for electrical conductivity as compared to that required to impede polymer mobility. The measurements of mechanical properties indicate that this processing method can obviously improve the tensile strength and the modulus of the composites.