A silanized organoclay (s-M-2(HT)(2)) was prepared by reaction of trimethoxyphenyl silane with an organoclay with a M-2(HT)(2) surfactant structure. Nanocomposites were formed from polypropylene (PP) and a blend of PP and maleic anhydride-grafted polypropylene (PP-g-MA) and the M-2(HT)(2) and s-M-2(HT)(2) organoclays by melt processing to explore the extent of exfoliation and the mechanical properties. Wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) coupled with detailed particle analysis were used to determine the effect of the organoclay used and the PP-g-MA compatibilizer on exfoliation and mechanical, rheological, and thermal expansion properties. The PP/s-M-2(HT)(2) nanocomposites have higher particle densities than the PP/M-2(HT)(2) nanocomposites though the aspect ratio remains the same. Platelet dispersion is significantly improved by using PP-g-MA compatibilizer for both organoclays. The rheological properties and the relative modulus improve for the PP/s-M-2(HT)(2) nanocomposites but not to the same degree as either organoclay in a PP-g-MA compatibilized matrix. The thermal expansion properties, however, are not improved by using the s-M-2(HT)(2) organoclay. The s-M-2(HT)(2) organoclay is less prone to agglomeration during extrusion than the M-2(HT)(2) organoclay. (C) 2011 Elsevier Ltd. All rights reserved.