Clay containing polypropylene (PP) nanocomposites were prepared by direct melt mixing in a twin screw extruder using different types of organo-modified montmorillonite (Cloisite 15 and Cloisite 20) and two masterbatch products, one based on pre-exfoliated clays (Nanofil SE 3000) and another one based on clay-polyolefin resin (Nanomax-PP). Maleic anhydride-grafted polypropylene (PP-g-MA) was used as a coupling agent to improve the dispersability of organo-modified clays. The effect of clay type and clay-masterbatch product on the clay exfoliation and nanocomposite properties was investigated. The effect of PP-g-MA concentration was also considered. Composite morphologies were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM), and transmission electron microscopy (TEM). The degree of dispersion of organo-modified clay increased with the PP-g-MA content. The thermal and mechanical properties were not affected by organo-modified clay type, although the masterbatch products did have a significant influence on thermal and mechanical properties of nanocomposites. Intercalation/exfoliation was not achieved in the Nanofil SE 3000 composite. This masterbatch product has intercalants, whose initial decomposition temperature is lower than the processing temperature (T similar to 180 degrees C), indicating that their stability decreased during the process. The Nanomax-PP composite showed higher thermal and flexural properties than pure PP. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2013-2025, 2011