Brillouin Scattering and Tribological Study of PMMA/SiO2 Nanocomposite

In recent years, nanocomposites materials, and in particular polymer nanocomposites have been developped for various applications, as high mechanical strengh, enhanced tribological properties and fire retardency [1-5]. These new materials could be used for extreme conditions in many industrials fields. Indeed, nanocomposites may combine the beneficial properties of polymer (easy shaping and low cost processing), with those of inorganic particles. The nanofillers may allow for tailoring the material according to the required properties (mechanical, tribological, optical, dielectric, etc.). In particular, due to the possible wide interphases between polymer and nanoparticles, some of the mechanical properties may be highly enhanced as fracture toughness or impact strength. Tribological applications could also potentially benefit from the development of polymer-based nanocomposites used as coatings. Therefore, some nanocomposites are beginning to be used as sliding elements in bulk or coating forms [2, 5]. In this work, we study PMMA/SiO2 nanocomposites, prepared for industrial applications. Our analysis deals with friction and wear tests on the one hand and with Brillouin spectroscopy (BS) on the other. The latter is used to assess the exact elastic coefficient of the materials, which it has already been used for with materials ranging from crystalline to amorphous, including composites [6-10]. One of the main objectives of building such polymer-based nanocomposites is to enhance the wear performance of the polymer matrix. However, to obtain this effect, it is necessary to have a well incorporated powder, which means that the powder needs to be embedded into the matrix with efficient chemical bonds. In our case, silanisation was performed in order to improve the ability of the particles to react with the matrix. Therefore, in this study, the effects of the concentration of SiO2 nanoparticles and their surface treatment on the elastic properties, friction, and wear behaviour were investigated. Two kinds of samples were compared, with silanised SiO2 fillers and with nonsilanised SiO2 fillers. The nanoparticles used to prepare the nanocomposites are SiO2 nanoceramic synthesized by the company DGTec through precipitation from tetraethyl orthosilicate (TEOS). This process allows DGTec to produce monosized ball-shaped nanoparticles in a choice of size ranging from 30 nm to 500 nm. In this study, nanopowders of less than 200 nm size were used in pure or silanised form. After the drying of the powder, silanisation was carried out by DGTec using methoxy-silane: silane Z-6011 (3-Aminopropyltriethoxysilane, Dow Corning) was used on the dried powder and stabilized with a low temperature treatment (70 °C). Masterbatches of nanocomposite at 2wt% were realised in a doublescrew extruder with pellets of pure PMMA. Two masterbatches were prepared, with non-silanised SiO2 and silanised SiO2. Other concentrations, i.e. 0.1, 0.5 and 1wt%, were obtained by the extrusion Names 2007, 3rd France-Russia Seminar