Quantitative mapping of mechanical properties in polylactic acid/natural rubber/organoclay bionanocomposites as revealed by nanoindentation with atomic force microscopy

Quantitative mapping of the mechanical properties of a series of polylactic acid/natural rubber/organoclay bionanocomposites has been accomplished by using nanoindentation with atomic force microscopy. Topography, elastic modulus and adhesion maps were obtained simultaneously revealing nanoscopic mechanical features in the samples associated to the different phases. For polylactic acid and polylactic acid/natural rubber a single distribution of Young's moduli was obtained whose maximum correlates well with the macroscopic measurements. Bionanocomposites with high organoclay loads exhibit a bimodal distribution of elastic moduli whose maxima can be associated to the polylactic acid matrix and to the reinforcing levels provided by the organoclay component. Adhesion maps allow one to obtain mechanical contrast between polylactic acid and organoclay, at high loadings, revealing the good compatibility of the organoclay with the polymer.