Analysis MethodProcessing and nanodispersion: A quantitative approach for polylactide nanocomposite

In this work, the nanodispersion of organomodified montmorillonite (MMT) in polylactide (PLA), prepared by varying the processing conditions, is investigated by solid-state nuclear magnetic resonance (NMR). The method is based on T1H (proton longitudinal relaxation time) measurement as a quantitative indicator of the dispersion. It permits extraction of two parameters: (i) f is the fraction of the potentially available clay surface, which has been transformed into polymer/clay interfaces and (ii) ε is a relative measure of the homogeneity of the dispersion of these actual polymer/clay interfaces. The NMR approach is consistent with transmission electron microscopy (TEM) results but, as a bonus, NMR allows providing of a quantitative view of the whole sample, while TEM is mainly qualitative and looks only at a tiny volume of the material. This critical advantage is used, for the first time, to quantitatively investigate the influence of the processing conditions on the nanomorphology of PLA/MMT nanocomposite. It is revealed that high mechanical energy for a short time (∼1 min) followed by low shear stress for a reasonable residence time (∼5 min) results in the delamination of the clay platelets (high f value) associated with a very high degree of homogeneity (ε=97%). Longer times and higher shear lead to the reagglomeration of the platelets.