PET nanocomposites were prepared using montmorillonite with different organic modifiers (Cloisite (R) 15A, 30B and 10A). TEM, WAXD and DSC were used for the characterization. Nanocomposites of intercalated and exfoliated morphologies were obtained, and an average maximum distance between the platelets was observed in the intercalated morphology. The clay nucleated the PET crystallization process, and the nucleating effect was higher when Cloisite 10A was used. This study allowed the evaluation of the characteristics of the organic modifiers' influence on the intercalation and exfoliation processes in PET. Tactoids were obtained when only apolar modifiers were present. It was observed that PET nanocomposites were intercalated and exfoliated when polar modifiers were present. (c) 2007 Elsevier Ltd. All rights reserved.