Polymer nanocomposites and intercalated flame retardants. New approaches to reduce plastics combustibility

摘要

Polymer filled with low amount of layered silicate disperse at nanoscale level are most promising materials characterised by a combination of chemical, physical and mechanical properties that can not be obtained width macro- or microscopic dispersions of inorganic fillers.Polymer layered silicate nanocomposites can be obtained by insertion of polymer molecules in the galleries between the layers of phyllosilicate. Here, hydrated alkaline or alkaline earth metal cations are hosted which neutralise the negative charge resulting fromisomeorphous substitutions of Mg of Al cations within the silicate. 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-dipole method.A more general technique involves compatibilisation of the silicate by intercalation of an organic molecule, typically an organic alkyl ammonium salt, that replaces the cations in the interlayers 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 delaminated polymer-silicate hybrids are obtained depending on whether the stack organisation of the silicate layers is preserved or is lost, with single sheets being distributed in the polymer matrix.The methods currently used for preparing polymer layered silicate (PLS) nanocomposites are: in situ polymerization, from polymer solution or from polymer melt. Although PLS nanocomposites have been known for a long time, it is the possibility of preparing them by melt intercalation of OLS in processing that is boosting the present interest in these materials and their properties.So far PLS nanocomposites have been characterised by X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry, nuclear magnetic resonance. Published results on PLS nanocomposites are reviewed concerning their characterisation and properties with particular reference to fire retardant behaviour.