Fabrication et caracterisation de nanocomposites a matrice epoxy

This project deals with processing and characterization of epoxy based nanocomposites reinforced with carbon nanotubes and nanofibers, and with nanoclays and spherical nanosilicas. The main objective of this work is to gather the knowledge of polymer nanocomposite science, specifically epoxy nanocomposites, and develop an expertise in their processing and analysis of their properties. Since nanoparticles have a high potential of polymer matrix reinforcement, this project focuses on the demonstration of efficiency of nanoparticles use in high performance composites.;Another part of the work consisted in embedding nanoclays (layered nanosilicates) into an epoxy resin. Two processing methods were mainly used. The first one was dispersion of the nanoclays into acetone and the second one into the anhydride hardener, through ultrasonication and for two concentrations (1 and 4 wt%). The thermo-mechanical properties were not improved in any case. A significant decrease of the elastic modulus and Tg was even measured in case of 4 wt% dispersed in acetone. The residual traces of solvent after evaporation could be responsible for this result. This last process resulted in a non-Newtonian fluid, whereas the process including hardener dispersion resulted in a Newtonian fluid. The nano-modified resin viscosity doubled with 1 wt% and tripled with 4 wt%. X-rays diffractograms allowed evaluating the intercalation/exfoliation state of the nanoclay layers. The interlayer distance is larger for 1 wt% than for 4 wt%, suggesting that the higher the concentration, the harder it is to exfoliate clays. Nevertheless, the intercalation state is too weak to improve the matrix properties.;Finally, the study of spherical nanosilica particles has lead to a second article relating several properties of a nano-modified epoxy, like viscosity, kinetics of cure, thermomechanical properties like elastic modulus, Tg and thermal expansion as a function of filler content. Processing of samples containg up to 26 wt% was possible thanks to the absence of tendancy to agglomeration. Elastic modulus and CTE were greatly improved by the presence of nanosilica and this was not the case of Tg, which was even much lower after addition of high nanosilica content. The viscosity value doubled and reached a plateau after adding 5 wt% which is interesting for an injection process. Composite parts were made through VARTM process of the nano-modified epoxy and unidirectional carbon fibers. The mechanical tests performed on the processed parts did not show any clear improvement of the composite properties (impact). This result could be due to the choice of mechanical tests which does not allow detecting the efficiency of particles. (Abstract shortened by UMI.).;In the first article, the objective is to define the link between processing methods, dispersion quality and thermo-mechanical properties, with the help of dielectric measurements. To do so, several fabrication processes were used, varying separately carbon filler content, dispersion mode, ultrasonication time and surface treatment. Results have shown that for an ultrasonication time of 1h, only a low filler content is able to increase the elastic modulus as well as Tg. Moreover, a short time of acid treatment is able to improve the nanocomposite properties, since the particles are better dispersed. The increase of ultrasonication time induced a lower elastic modulus, but also a higher Tg and a better dispersion. A dispersion procedure into the amine hardener was revealed less efficient than the dispersion into ethanol. A quick characterization method through dielectric measurements was developed and was used to assess the dispersion state of the conductive fillers in the epoxy matrix. It was then possible to link the more drastic increase of electrical conductivity with the improvement of the dispersion observed through microscopy, for samples prepared with a long ultrasonication time. It comes out of this work that a better dispersion induces an increase of the thermo-mechanical stability (Tg), and the relative dispersions of two different fabrication processes can be compared through dielectric measurements.