| Summary: | Since their first observation in 1991, carbon nanotubes (CNTs) have attracted a lot of attention owing to their exceptional properties. Their excellent electrical and thermal conducting performances combined with their high toughness and transverse flexibility allow their use in a large range of varied applications. Offering at the same time a high aspect ratio (length-to-diameter) and a low density, carbon nanotubes show strong application potential in reinforced composite materials. Unfortunately, CNTs have the strong tendency to form bundles very difficult to dissociate and disperse in a majority of polymer matrices. Without efficient CNTs dispersion, nanocomposites can not present optimal mechanical, thermal and electrical properties. To overcome this drawback, one solution consists to graft polymer chains on the carbon nanotubes surface in order to disaggregate bundles and, in few cases, to improve interaction between the polymer matrix and nanotubes.
The thesis work can be divided into three parts. The first is the one-step amination of multi-walled carbon nanotubes (MWNTs) via an original microwave plasma process. The MWNTs, placed in the post-discharge chamber in presence of H2, are subjected to a reactive flow of atomic nitrogen produced by the plasma. The results give evidence for efficient covalent grafting of primary amine groups along the sidewalls of MWNTs, avoiding any structural damage and alteration of properties.
The so-grafted amine groups have been further consider as initiation sites for promoting the ring opening polymerization of lactone monomers yielding polyester-grafted MWNT nanohybrids.
Finally, these nanohybrids have been used as highly filled masterbatches to be dispersed in the molten state within several polymer matrices, such as polycaprolactone (PCL) and high density polyethylene (HDPE), to obtain nanocomposites with largely improved properties. For instance, electrical measurements and morphological characterizations showed that the polyester surface-grafting allows for improving the dispersion state of the nanotubes in the different polymer matrices leading to enhanced electrical properties as well as thermal and mechanical performances.
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