Synthesis and properties of polylactide/clay nanocomposites

Abstract

In this dissertation, the development of polylactide as a commodity plastic was studied by the introduction of modified clay into the high molecular weight commercial polylactide. The improvement of shear thinning, thermal stability and mechanical properties of polylactide/modified clay nanocomposites was mainly focused. In contrary to the conventional polylactide/clay nanocomposites system, commercialized clay with hydroxyl-functionalized ammonium cations groups was modified by grafting different molecular weight of polylactide by ring-opening polymerization using the reactive extrusion concept in order to make production of polylactide or modified clay economically viable and then melt compounded with high molecular weight of polylactide for the preparation of polylactide/clay nanocomposites. The effect of the lactide-modified clay on the properties of the nanocomposites such as the morphology, rheological properties, thermal properties and mechanical properties of the nanocomposites was investigated. Lactide-modified clay was synthesized using L-lactide and commercialized organoclay $(Closite^{\reg}30)$ with the equimolar complex of $Sn(Oct)_2$ as a catalyst and triphenyphosphine as a co-catalyst. The product yield was over 97% even though residence time was as short as 10min. That resulted form the support of mixing element and the shearing of the polymer as well as catalyst and co-catalyst which had a favorable effect on polymerization rate and delayed the occurrence of undesirable back biting reaction. Lactide-modified clay showed exfoliated or partially intercalated structure by the grafting reaction of the growing polylactide chains onto the clay surface which affected the high degree of exfoliation of polylactide/lactide-modified clay nanocompsoites. In polylactide/modified clay nanocomposites system, it showed the improvement of the shear thinning compared to the polylactide and conventional polylactide/clay nanocomposites when molecular weight of...