Nanostructure vs. microstructure: Morphological and thermomechanical characterization of poly(l-lactic acid)/layered silicate hybrids

Nano- and micro-composites of poly(l-lactic acid) (PLLA) with various loadings of natural and hexadecylamine-modified montmorillonite were prepared by the solvent casting method to study the effect of nanostructure on the thermomechanical properties of the hybrid materials. The changes on structure and surface of montmorillonite, induced by the ion-exchange modification process, were characterized by X-ray diffraction (XRD) analysis and zeta-potential determination, while the morphology of the hybrids and the dispersion of the clay into the polymer matrix were examined by XRD, transmission electron microscopy and atomic force microscopy. The results showed that, although at low clay content exfoliation dominates, for filler loadings greater than 5 wt% both exfoliation and intercalation of the clay filler are observed. Thermal degradation studies of the materials produced using thermogravimetry revealed the introduction of a small amount of organo-modified silicate significantly improves their thermal stability. Differential scanning calorimetry showed the thermal behavior of the polymer matrix strongly depends on the nature and content of the silicate filler. Scanning electron microscopy of the deformed surfaces affirmed a different deformation process mechanism between the two types of composites.