Composites with lamellar nanofillers

Nanocomposites can consist of a dispersion of generally clayey platelets or lamellae in a polymer matrix. These lamellar fillers are made up of a set of sheets ("mille feuilles" type). The dimensions of the individual sheets are of the order of nanometers in thickness, several tens of nanometers in width, and several tens of nanometers to a few micrometers in length, hence their name nanocharges. These dimensions give them a very high surface coefficient (from 100 to 1,000 m ² · g ^-1 ) and a very high form factor (length/thickness > 100). The geometrical characteristics of the filler have a decisive influence on the properties of the polymer materials formulated in this way, which are listed here under the general name nanocomposites, to take account of the nanoscopic dimension of the fillers introduced, and not to be confused with traditional polymer/reinforcement fiber composites (e.g. polyester/glass fibers).

Depending on the state of exfoliation and dispersion of the mineral filler in the matrix, three types of mineral structures can be distinguished:

• a non-exfoliated structure, when the sheets remain agglomerated in the form of packets (or a crystal);

• an interleaved structure, with incompletely separated sheets;

• an exfoliated (or delaminated) structure with well-separated, well-dispersed individual sheets (resulting in a loss of crystalline coherence).

After some general information on lamellar nanofillers (§ 1 ), we will describe lamellar nanocomposites in turn:

• based on polyamide (PA), § 2