Homogeneously dispersing rigid particles in polymer matrices is a very common and widely used method that allows for readily increasing the stiffness of the so-obtained composite materials. Depending on the intrinsic nature of the added filler, other properties can also be enhanced such as fire resistance, electrical and thermal properties. However, such improvements of composite materials performances usually require high filling levels, detrimental to the ultimate mechanical properties of the resulting materials.
Polymer nanocomposites represent a new class of composite materials, i.e., particle-filled polymers for which at least one dimension of the dispersed particles is in the nanometer range. This variety of nanofillers provides the related composite materials with significantly improved properties most often at filler content as tiny as 3 to 5 wt%. Interestingly, remarkable thermo-mechanical performances have been recorded using organo-modified layered silicates (organoclays) as nanofiller precursors. Actually, upon incorporation of such organoclays in a polymer matrix, intercalation of the polymer chain in-between the clay platelets or complete exfoliation of the silicate platelets can be observed. Exfoliated nanocomposites usually exhibit significantly higher improvement in properties such as mechanical, thermal and flame retardant properties. However in many polymeric matrices, reaching such large extent of organoclay exfoliation and dispersion still remains a difficulty.
More recently discovered carbon nanotubes constitute another family of potential nanofillers for polymer matrices. Carbon nanotubes are mainly subdivided in two families: single-walled nanotubes (SWNTs) or multi–walled nanotubes (MWNTs) where several nanotubes of decreasing diameter are interlocked. Carbon nanotubes find applications in various fields such as in field emission devices, electrically and thermally conductive materials, hydrogen storage devices and molecular sieves. Even though carbon nanotubes have already been blended within various polymers, homogeneous dispersion of the nanotubes in the polymer matrix remains one major challenge, since bundles of aggregated SWNTs or MWNTs most often persist and therefore limit the performances of the recovered composite materials.
This contribution aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-based nanocomposites filled with either organoclays and/or carbon nanotubes. Undoubtedly, the key-challenge remains to reach a high level of nanoparticle dissociation (i.e., either to delaminate the silicate nanoplatelets or to break down the bundles of aggregated carbon nanotubes) and their fine dispersion upon melt blending within the selected polymer matrix. In that context, the in situ polymerization/grafting process as catalyzed directly from the nanofiller (organoclay or carbon nanotube) surface proved highly efficient allowing for the complete destructuration of the native filler aggregates. Dissociated nanoparticles were accordingly recovered, their surface was homogeneously coated/grafted by the in situ grown polymer chains as generated by this so-called “Polymerization-filling technique” (PFT). Interestingly enough, such surface-coated organoclays and/or carbon nanotubes were further added as “masterbatch” in commercial polymeric matrices by twin-screw extrusion. As a result of the pre-destructuration of the nanofillers by PFT, it comes out that the resulting polymer nanocomposites displayed much higher thermo-mechanical properties even with a nanofiller loading as tiny as 1wt%.
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