CONICET | Buscador de Institutos y Recursos Humanos

Polymeric nanocomposites are a new class of materials, for which at least one dimensions of the dispersed particles, is in the nanometer range. Their dimensions typically range from 1 to 100 nm. They represent an interesting alternative to conventional polymer composites because of their unique properties, synthesis and processing methods. Among all the potential nanofillers studied in the past decades, clays occupy an important position because they are easily available on all the continents with relatively low cost. Between smectites, bentonite has been extensively used to prepare organoclays due to its high cation exchange capacity, swelling behavior, adsorption properties and large surface area. Dispersing clays in polymers at the nanoscale, even at loadings of only 1 to 5 wt. %, provides considerable improvements in polymer properties compared with conventional micro particle fillers including, for example, higher modulus both in solid and melt state, increased strength and thermal stability, decreased permeability and increased biodegradability (Alexandre and Dubois, 2000). The main reason for these enhanced properties in nanocomposites is the stronger interfacial interaction between the matrix and layered silicate. In order to achieve these better properties it is necessary to obtain a totally exfoliated structure (this means that the silicate layers are completely and uniformly dispersed in the continuous polymeric matrix). Hence, the high aspect ratio of the nano-scale layered silicate and their dispersion in the polymer plays a key role in these improvements. Nanoclay particles are generally agglomerated as a result of their high surface energy, therefore the disaggregation of nanoparticle agglomerates before or during composites processing proves to be a key point in obtaining an optimal dispersion (Rong et al., 2006). Although there are different ways to optimize the polymer/clay compatibility, the most popular method consists on converting these hydrophilic silicates to organophilic ones by performing chemical treatments of the clay. The synthesis of organoclays is based on the mechanisms of the reactions that the clay minerals can have with the organic compounds. ? Ion exchange of the interlayer inorganic cations with organic cations (usually with quaternary ammonium or alkylphosphonium compounds) is a relatively simple industrial treatment to alter the surface properties of the clay. In addition, these cations can provide functional groups that eventually can react with the polymer matrix or initiate a polymerization reaction, improving the strength of the interface between the inorganic platelet and the polymer matrix. ? Grafting reactions, i.e., forming covalent bonds between reactive surface groups and organic species, are important steps to hydrophobise the surface of many clay mineral particles. Trialkoxysilanes and alkylchlorosilanes can be used to modify the clay surface due to their ability to readily undergo hydrolysis and condensation reactions. It has been proved that the quantity of grafted silane can be greatly enlarged by the acid activation of clays; this feature could be related with the increment of reactive sites generated through acid treatment. In this work, several strategies to modify bentonite and to make it more compatible with polymeric matrices were studied: cation exchange reactions with different alkylammonium and alkylphosphonium salts and grafting reactions with a various silane compounds. The effect of each modification, together with the relevant parameters, was established. In order to evaluate the effectiveness of the modifications, the obtained organoclays were chemically (FTIR spectroscopy), morphologically (X-ray diffraction, water absorption studies) and thermally (thermogravimetric analysis) characterized and the effects of each treatment were analyzed. This work was performed under the project FSNano004: ?Development of modified nanoclays and innovative products from national clays?.