HMS-Polypropylene (high melt strength polypropylene) is a polypropylene modified by gamma irradiation and acetylene. In this process PP is modified for synthetized long chain branching. The clay utilized is the Cloisite 20 and PP-g-MA (polypropylene graft maleic anhydride) as coupling agent. The processing was carried in twin screw extruder for dispersion of the clay particles in the polymer matrix. The dumbbell samples was settled in device for environmental exposition and exposed in period of 6 months; and in accelerated condition, was utilized the stove with air circulation at 110 °C to evaluate thermal stability. The chemical changes in the samples were evaluated for Carbonyl Index by FT-IR (Fourier Transformed Infrared Spectroscopy), DSC (Differential Scanning Calorimetry) and Thermogravimetry (TGA) regarding the effects of degradation on thermal properties. The dispersion of clay was analyzed by X-ray Difraction (DRX) and Transmission Electronic Microscopy (TEM). The lower content of clay showed higher degradation rate under stove exposition, awhile under the environmental exposition lower content of clay showed distinct behavior.