Polylactide/montmorillonite nanocomposites : study of the hydrolytic degradation

Hydrolytic degradation of polymer layered silicate nanocomposites based on polylactide matrix (PLA) and (organo-modified) montmorillonites was investigated in phosphate buffer solution for more than five months. While natural unmodified montmorillonite-Na+ led to the formation of a microcomposite, mainly intercalated nanocomposites were prepared by melt blending PLA with 3 wt% of montmorillonite organo-modified either by 2-ethylhexyl (hydrogenated tallowalkyl) ammonium cations (Cloisite®25A) or by bis-(2-hydroxyethyl) methyl tallowalkyl ammonium cations (Cloisite®30B). The evolution of molecular weight of the matrix as well as its crystallinity with the hydrolysis time has been recorded by size exclusion chromatography (SEC) and differential scanning calorimetry (DSC), respectively. Thermogravimetric analyses (TGA) performed on the microcomposite based on Cloisite®Na+ has shown that the thermal stability of the materials decreased proportionally to the decreasing PLA molecular weight along the hydrolysis time. Moreover, in parallel to the morphology of the composites, the relative hydrophilicity of the clay layers has been shown to play a key role in the hydrolytic degradation of the PLA chains.