Quantitative Structural Characterization of Polymer-Clay Nanocomposites and Discussion of an ''Ideal'' Microstructure, Leading to the Highest Mechanical Reinforcement

Montmorillonite and other lamellar materials are very promising for reinforcing semicrystalline thermoplastics, especially if exfoliation is achieved. To understand the macroscopic properties of polymers filled with lamellar materials, it is unavoidable to characterize their structures. Parameters have to be determined such as the clay dispersion state, the orientations of the clay and of the polymer crystalline lamellae, and the interactions between the clay and the polymer matrix. Beyond the over-simple description as ''intercalated'' or ''exfoliated'' structures, we ropose a multiscale characterization of the state of exfoliation of the clay platelets based on the analysis of Optical Microscopy and Transmission Electron Microscopy images. The results have been confirmed by Small Angle X-Ray Scattering, which also gives pieces of information regarding the orientation of the clay platelets and of the polymer crystalline lamellae. Lastly, we propose the use of Dynamic Mechanical Analysis (DMA)as an indirect technique to probe the filler/matrix interfacial adhesion strength. In the light of these characterizations, we discuss a structure which is thought to lead to the highest reinforcement below and above Tg.