A high-density polyethylene (HDPE) masterbatch containing 20.2 wt% multiwalled carbon nanotubes (MWNTs) was melt diluted with neat HDPE using two different methods: a twin screw microcompounder and a single-screw extruder. The electrical properties of these composites were assessed using bulk electrical conductivity measurements, their mechanical properties were evaluated using tensile tests and dynamic mechanical analysis (DMA), and percent crystallinity was determined by wide angle x-ray diffraction (WAXD) and differential scanning calorimetry (DSC). A percolation threshold (pc) of 4.5 wt% MWNTs was found in compression-molded samples. Extruded samples were prepared with nanotube concentrations below and above the compression-molded percolation threshold (2 and 7 wt% MWNTs) and passed through the extruder twice before entering a low-shear melt annealing zone. Different melt annealing times were used and their effects on the electrical and mechanical properties of the resulting quench-cooled composites were evaluated. Results showed that extruded composites were nonconductive, indicating that a conductive nanotube network did not form on the time scale of these experiments. Annealing time also did not affect significantly the mechanical properties of the resulting solid composites. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers