Maleic anhydride grafted polypropylene (PPgMA) reinforced by layered silicates was studied using rheological investigation techniques, to probe the degree of exfoliation of the clay particles in the melt state at 190 degrees C. The rheological properties of the composites were investigated as a function of the ageing time and interpreted in terms of degree of dispersion of the clay platelets in the maleic anhydride modified polypropylene matrix. The interpretation in terms of exfoliation degree was confirmed by wide angle X-ray scattering and nano-secondary ions mass spectroscopy experiments. Chemical reaction, promoted by oxygen, of maleic anhydride with hydroxyl groups located on clay platelet edges, is one of the major mechanisms involved in the exfoliation process highlighted in this study. PP chain segment thermal motions as well as moderate shear were shown to be required in order to achieve clay exfoliation. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 4011-4019, 2009