Influence of MWNT on the physical properties of polyethylene nanocomposites

Physical properties of a series or multi-walled carbon nanotube-high density polyethylene (MWNT-HDPE) composites, prepared by melt mixing in a micro-twin screw extruder, were investigated. The effect of MWNT concentration (0.5-7 wt%) and nanotube surface treatment (oxidative treatment in a tubular furnace at 500 degrees C for 1-2 hr in a 95% nitrogen, 5% oxygen atmosphere) was investigated by several experimental techniques. Scanning electron microscopy showed good adhesion and dispersion of nanotubes in the matrix, independently of the surface treatment. TG analysis suggests that the incorporation of MWNT in the polymer results in increased oxidative stability. Electrical and rheological measurements showed that the oxidative treatment, causing some reduction of the MWNT quality (indicated by Raman Spectroscopy), decreases the efficiency of the nanotube-matrix interaction. The evaluated electrical percolation threshold is in good agreement with rheological percolation threshold. The isothermal quiescent crystallization, studied by rheometric techniques, clearly indicates that increasing the MWNT concentration in the composite the onset of crystallization occurs earlier. Such a behavior confirms the nanotube nucleant effect previously observed by non-isothermal DSC. Finally, flow induced crystallization has been investigated.