Polymer layered silicate nanocomposites

Polymers filled with low amounts of layered silicate dispersed at nanoscale level are most promising materials characterized by a combination of chemi cal, physical and mechanical properties that cannot be obtained with macro- or microscopic dispersions of inorganic fillers. Polymer layered silicate nanocomposites can be obtained by insertion of polymer molecules in the gal leries between the layers of phyllosilicate. Here, hydrated alkaline or alk aline earth metal cations are hosted which neutralize the negative charge r esulting from isomorphous substitutions of Mg or Al cations within the sili cate. Insertion of polymer molecules to prepare "intercalation hybrids" can be carried out by replacing the water hydration molecules in the galleries by polymers containing polar functional groups, using the so called ion-di pole method. A more general technique involves compatibilization of the sil icate by intercalation of an organic molecule, typically an organic alkylam monium salt, that replaces the cations in the interlayer galleries to form an organically modified layered silicate (OLS). The aliphatic chain of the OLS favors the intercalation of any type of polymer. Intercalated or delami nated polymer-silicate hybrids are obtained depending on whether the stack organization of the silicate layers is preserved ol is lost, with single sh eets being distributed in the polymer matrix. The methods currently used fo r preparing polymer layered silicate (PLS) nanocomposites are: in situ poly merization, from polymer solution, or from polymer melt. Although PLS nanoc omposites have been known for a long time, it is the possibility of prepari ng then by melt intercalation of OLS in processing that is boosting the pre sent interest in these materials and their properties. So far PLS nanocompo sites have been characterized by X-ray diffractometry, transmission electro n microscopy, differential scanning calorimetry, and NMR. Published results on PLS nanocomposites are reviewed concerning their characterization and p roperties with particular reference to fire retardant behavior.