Polymer/clay nanocomposites are investigated using mainly thermoplastic polymers such as polyamide-6, polyethylene, polypropylene, … Much less attention has been paid to rubbers and rubber-like materials. Our objective is to define parameters controlling clay exfoliation in elastomer matrices by direct blending. The latter condition implies no solvent use in the blend together with preserving maximum exfoliation to a single layer level.
Barriers hindering rubber incursion inside clay structure are identified as due to the characteristics of the clay on the one hand (hydrophilicity, surface free energy, interlayer gap, ion exchange capacity,…), and of the polymer on the other hand (hydrophobicity, surface free energy, molecular weight and molecular weight distribution,…).
In this work we present an attempt to overcome such obstacles by three major means :
- clay synthesis
- chemical modification of the synthesized clay
- chemical modification of the polymer and MW variation
Since natural clay, as all natural products, suffers from a lack of reliability, and therefore exhibits an experimental irreproducibility, we chose to synthesize our clay in the laboratory. Thus, the sodium form of a montmorillonite-type [Na_0.3(Al_1.7Mg_0.3)Si₄O₁₀(OH)₂] clay (Mmt) was prepared by hydrothermal synthesis in hydrofluoric acid medium at 20 °C for 48 hours in a stainless steel PTFE lined autoclave. Further selection and control of the particle size and its influence was investigated.
Clays are basically hydrophilic materials, as a consequence they cannot be blended properly with hydrophobic matrices such as elastomers. Two ways of material modification can be anticipated to overcome this dilemna:
- grafting the rubber with species having natural affinity for the clay and/or
- converting the clay into an organophilic material by cation exchange treatment.
Both ways were investigated, chemical structures were controlled by elemental and TGA analysis, exfoliation was monitored by X-ray diffraction TEM and rheological measurements and hybrid composites were tested by dynamic mechanical thermal analysis.Results will be discussed in term of modification/exfoliation relationship as well as polymer/clay-monolayer adsorption and hybrid three-dimensional network formation.

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