Non-Hydrolytic in situ synthesis of new polyolefin-based nanocomposites by reactive extrusion – SYNCOPE

Polymer nanocomposites have been used commercially since Toyota introduced the first polymer/clay nanocomposite in auto parts in the 1980s. It is clearly established now that the addition of submicronic particles can improve structural and functional properties in a number of polymer based systems, providing an answer to ever increasing requirements from advanced industrial sectors. However several fundamental issues remain opened especially when concerned with the polyolefin based nanocomposites elaboration. In the “top-down” approach, corresponding to the dispersion of the filler into the polymer, the main problems are linked to the difficulty to reach a homogeneous and complete dispersion of the nanoparticles and to the increasing environmental and societal concerns about the manipulation of these nanoobjects. To address these problems, numerous efforts have been focussed on the improvement of matrix-particle interactions using compatibilizers, surface modification of the filler, or special processing conditions. In parallel, some attempts to associate hydrolytic sol-gel chemistry and polyolefins in a “bottom-up” approach have been found promising notably because this approach avoids the manipulation of nanoobjects. However, we are still confronted with the difference of nature between the hydrophobic character of the polyolefins and the hydrophilic character of the inorganic phase leading to the agglomeration of the nanoparticles. In this context, the project SYNCOPE proposes the development of new polyolefin-based nanocomposites combining reactive extrusion and non hydrolytic sol-gel chemistry for the in situ creation of the nanofiller. This one-step process, avoiding any nanoparticle manipulation, is based on thermoactivated reactions in which reactants are compatible within the molten polyolefin. The surface of the created nanofiller is not hydroxylated, which prevents aggregation and should improve the dispersion within the polyolefin. The SYNCOPE project proposes to synthesize two types of nanocomposites with increasing complexity. First, we will focus on the in situ synthesis of a metal oxide such as titanium dioxide, TiO2, and the influence of specific surfactants (oligomers functionalized by carboxylic or phosphonic acids) able to interact with the growing inorganic phase and impact the size, shape, and dispersion within the polymer matrix of the nanoparticles. Secondly, we will synthesize lamellar nanofillers such as metal phosphonates. The impact of these different aspect ratios and organic/inorganic interfaces on barrier properties will be thoroughly investigated. Diffusing molecules varying by their size and interaction capacity will be used as an original way to probe the organic/inorganic interface developed in these new nanocomposites. Finally, this approach should offer a new field of investigation in view of different applications such as packaging, or automotive for example.