We present a novel approach to improving organoclay exfoliation in a nonpolar matrix, polyethylene. High-density polyethylene (HDPE) particles were modified by exposure to a reactive gas atmosphere containing F-2 and O-2. This treatment was aimed at increasing the polarity of the polymer with the formation of carboxyl, hydroxy, and ketone functionalities on the particle surface. The surface-treated high-density polyethylene (ST-HDPE) particles were then melt-mixed with an appropriate organoclay to form nanocomposites. Transmission electron microscopy (TEM), wide-angle X-ray scattering, stress-strain analysis, and Izod impact measurements were used to evaluate the nanocomposite morphology and physical properties. These data were compared to those of equivalent nanocomposites prepared from unmodified HDPE and high-density polyethylene grafted with maleic anhydride (HDPE-g-MA). The nanocomposites prepared from the ST-HDPE particles exhibited much better properties and organoclay dispersion than those prepared from unmodified HDPE. The level of reinforcement observed in ST-HDPE-based nanocomposites was comparable to, if not better than, that seen in HDPE-g-MA-based nanocomposites. However, a comparison of the TEM micrographs suggested better organoclay exfoliation in HDPE-g-MA than the current version of ST-HDPE. (c) 2006 Wiley Periodicals, Inc.