Ionic liquids based on tetraalkylphosphonium and dialkyl imidazolium cations with long alkyl chains have been investigated as new surfactant agents for cationic exchange of lamellar silicates. The effect of the chemical nature of the ionic liquids on the thermal stability and on the surface energies of phosphonium-(MMT-201) and imidazolium-(MMT-I) treated montmorillonites have been studied by thermogravimetric analysis (TGA) and sessile drop method. Poly(butylene adipate-co-terephthalate) (PBAT) nanocomposites filled with a low amount of these modified-montmorillonites (2, 5 wt%) have been processed by melt mixing using a twin screw extruder. The mechanical, thermal, water and gas barrier properties of the corresponding nanocomposites as well as the distribution of the clay layers in PBAT matrix were determined.