In this work a careful investigation on the degradation of an organically modified montmorillonite sample (Cloisite 15A) thermal treated under different atmospheres, namely nitrogen, air and oxygen enriched atmosphere was performed. The exposure time of the thermal treatment ranged between 5 and 300 min. The chemical composition evolution as function of the thermal treatment conditions of the clay organic modifier was monitored by means of combined thermogravimetry/Fourier transform infrared spectroscopy (TGA-FTIR). Moreover, the morphological behaviour of treated Cloisite 15A samples as function of the time and of the decomposition atmosphere was investigated by X-ray diffraction analysis (XRD). In order to understand the possible different interactions of neat and degraded modified clay with a polymeric matrix, PA6 based composites containing 5% of clay were prepared in the melt and fully characterized by a rheological, mechanical and morphological point of view. The results showed that during the thermal treatment the organic modifier in the interlamellar spaces undergoes a rearrangement, while the external unbound modifier degrades. At long exposure times, the degradation gradually extends to the clay galleries involving the internal modifier. These effects are more intense, as expected, when increasing oxygen concentration of the treatment atmosphere. As expected, the properties of the prepared nanocomposites were influenced by the degradation level of the incorporated clay. In particular, the morphology and mechanical properties of the composites worsened by increasing the time of the thermal treatment of the clay. (c) 2012 Elsevier B.V. All rights reserved.