Nanocomposites is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometres, or structures having nanoscale repeat distances between the different phases that make up the material. Polymer layered-silicate nanocomposites (PLSNs) with silicate enhance mechanical properties, increase heat-distortion temperatures, improve thermal stability, decrease gas/vapour permeability and reduce flammability [12]. The use of P-N flame-retardant with montmorillonite (MMT) as a flame-retardant synergist for flame-resistant thermoplastics such as PP, PA6, and PA66 has been reported [13]. Chemically, montmorillonite is hydrated sodium calcium aluminium magnesium silicate hydroxide (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2•nH2O. Montmorillonites swell or expand considerably more than other clays due to water penetrating the interlayer molecular spaces and concomitant adsorption. By exchanging sodium cations for organic cations the surface energy of MMT decreases and the interlayer spacing expands. The resulting material is called organoclay [14].
Thermoplastic poly(ester ether) elastomers (TPEEs) are easily ignited and rapidly burned. TPEE nanocomposites with phosphorus-nitrogen (P-N) flame retardants and organic montmorillonite (o-MMT) were prepared by melt blending. A significant fire-retardant effect was induced in TPEE and rendered a V-0 classification in the UL 94 test [15]. Organically treated layered silicates (clays), carbon nano-tubes/nano-fibres, or other submicron particles at low loading (1-10wt%) are used for polymer nanocomposites. The polymer nanocomposites greatly lower the base flammability of a material. Recent research has suggested that combining nanoparticles with traditional fire retardants (e.g., intumescent) or with surface treatment (e.g., plasma treatment) effectively decreases flammability [16].
When polymer nanocomposite is used, very little additive is needed (no great cost increase) and polymer dripping/flow while burning is reduced. The composite may have multifunctional performance (ex: electrical conductivity from carbon nanotubes) and a balance between flammability and mechanical properties may be maintained. However, careful design and analysis is required for set up of a polymer nanocomposite structure. Many aspects of nanocomposite technology (long-term ageing, environmental hazards, conservation of fire safety principles etc.) are not known.
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