Full exfoliation of clay/high density polyethylene (HDPE) nanocomposites was successfully achieved with the aid of maleated HDPE (PE-g-MAn), by melt blending in a twin-screw extruder employing a long residence time configuration. The morphology of the composites was determined using wide-angle X-ray diffraction and transmission electron microscopy. The effects of clay content and state of clay dispersion on the rheological, tensile properties, and flame retardancy of nanocomposites containing very small amounts of clay, in the range of 0.05-1.0 wt %, were investigated in this study. It was demonstrated that achieving a higher degree of exfoliation for nanosized clay particles is key to enhancing the rheological, mechanical, and flame retarding properties even when small amounts of clay (less than 1%) are used. (c) 2007 Wiley Periodicals, Inc.