Biodegradable poly(Lactic Acid)/clay nanocomposites by melt intercalation: A study of morphological, thermal, and mechanical properties

Biodegradable polymer nanocomposites of poly(lactic acid) (PLA) and several organically modified montmorillonites (nanoclays), namely, Cloisite 30B, Cloisite Na⁺, Cloisite 25A, Cloisite 20A, Cloisite 93A, and Cloisite 15A were prepared by melt compounding using a Brabender twin-screw extruder. An exfoliated morphology was observed using both X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) for the combination of PLA and Cloisite 30B (the montmorillonite modified with a quaternary ammonium salt). The first XRD peaks for all the other nanocomposites were observed to shift to lower angles, indicating that intercalation occurred. The extent of intercalation depended on the type of organic modification on the Cloisite organoclay and was exhibited in the sequence of Cloisite Na⁺ > 25A > 20A > 93A > 15A. Further studies were carried out to compare the properties of the PLA-30B nanocomposites with those of the neat PLA at clay loading levels of 1%, 2%, 3%, 4%, and 5% (w/w). Thermal stability of the nanocomposites was studied using thermogravimetric analysis (TGA). An increase in thermal stability was observed with a high at a loading level of 3% (w/w). Glass transition data were collected and analyzed using differential scanning calorimeter (DSC). An optimum in the glass transition temperature (T_g) of the nanocomposites was observed at 3% (w/w). Improvement in the mechanical properties of the nanocomposites was also observed.