Comparison of the influence of talc and kaolinite as inorganic fillers on morphology, structure and thermomechanical properties of polylactide based composites

• Examination of the interactions and affinity at the interface of polymer and clay.
• Relations between mechanical properties and affinity between clay and polymer.
• Relation between Zeta potential and clay dispersion.
• Enhancement of properties not only driven by dispersion degree.
• A proof of the interest of highly filled polymer nanocomposites.

This work deals with the effect of both nature and content of two chemically different layered silicates (i.e. talc and kaolinite) on the morphology, structure and thermomechanical properties of polylactide/clay minerals composites. Composites with filler contents up to 30 wt.% were studied. Regarding the morphology it was found that kaolinite–PLA nanocomposites display a better filler dispersion with a majority of particle sizes at the nanometer scale. This better degree of dispersion has been ascribed to the electrochemical properties of kaolinite which exhibit a lower Zeta potential than talc. It was also found that talc has a pronounced nucleating effect on PLA crystallization, whatever the clay mineral content. By contrast this effect is very limited in kaolinite–PLA nanocomposites. Investigation of the mechanical behavior indicates that a reinforcing effect is observed for the two types of clay minerals for filler contents beyond 10 wt.%. This shows the interest of filling PLA with high clay minerals contents. This reinforcing effect is significantly higher for the talc based composites. These differences are ascribed to a better affinity between PLA macromolecules and talc surface, due to the presence of only silicate layers. In addition to the demonstration of the interest of using high clay minerals loadings, a main result of this work is that filler dispersion is not the only parameter that governs the gain in properties. It is shown that interfacial effects and more especially affinity between the polymer and the clay mineral also play a key role.