Nanocomposite polymers, fire materials

Lewin, M., Some comments on the modes of action of nanocomposites in the flame retardancy of polymers . Fire Materials, 2003, 27, 1-7. 

Marosi, G., Keszei, S., Matko, S., and Bertalan, G. 2006. Effect of interfaces in metal hydroxide-type and intumescent flame retarded nanocomposites. In Fire and Polymers TV Materials and Concepts for Hazard Prevention, Vol. 922, eds. Wilkie, C. and Nelson, G. Washington, DC ACS, pp. 117-30. 

The materials included in this chapter for illustration are nanocomposite polymers combined with intumescent commercial phosphorous fire retardants. In this chapter, different base polymers (e.g., PA6, PBT, PP, and EVA) are mentioned for illustrating the methodology but the focus will be on PA6. For the present purpose, the composition of a PA6 nanocomposite is described next to make the development of the present methodology more clear. 

Morgan, A.B., Whaley, P.D., Lin, T.S., and Cogen, J.M., The effects of inorganic-organic cations on EVA-magadiite nanocomposite flammability in ACS Symposium Series 922, Fire and Polymers IV -Materials and Concepts for Hazard Prevention, Wilkie, C.A. and Nelson, G., (Eds.), American Chemical Society, Washington D.C., 2006, Chapter 5, 48-60. 

The fire toxicity of each material has been measured under different fire conditions. The influence of polymer nanocomposite formation and fire retardants on the yields of toxic products from fire is studied using the ISO 19700 steady-state tube furnace, and it is found that under early stages of burning more carbon monoxide may be formed in the presence of nanofillers and fire retardants, but under the more toxic under-ventilated conditions, less toxic products are formed. Carbon monoxide yields were measured, together with HCN, nitric acid (NO), and nitrogen dioxide (NO2) yields for PA6 materials, for a series of characteristic fire types from well-ventilated to large vitiated. The yields are all expressed on a mass loss basis. 

Polymer clay nanocomposites have, for some time now, been the subject of extensive research into improving the properties of various matrices and clay types. It has been shown repeatedly that with the addition of organically modified clay to a polymer matrix, either in-situ (1) or by melt compounding (2), exfoliation of the clay platelets leads to vast improvements in fire retardation (2), gas barrier (4) and mechanical properties (5, 6) of nanocomposite materials, without significant increases in density or brittleness (7). There have been some studies on the effect of clay modification and melt processing conditions on the exfoliation in these nanocomposites as well as various studies focusing on their crystallisation behaviour (7-10). Polyamide-6 (PA-6)/montmorillonite (MMT) nanocomposites are the most widely studied polymer/clay system, however a systematic study relating the structure of the clay modification cation to the properties of the composite has yet to be reported. 

Various workers have discussed the fire retardancy of polyvinylchloride (PVC) [55-59] using ammonium treated clay montmorillonite nanocomposites [52], hydroxyapatite nanocomposites [56] and antimony trioxide [57]. Lum [60] examined the effect of flame retardant additives on polymer pyrolysis reactions with a PVC composition containing 3 phr of SbiOs. It is well known that a synergistic flame retardancy effect is observed when SbiOs is incorporated into organic halide materials such as PVC. 

The demand for material properties to meet superior and more severe specifications has motivated vigorous research on polymer nanocomposites, that is, polymer matrices incorporated with fillers with at least one dimension in the nanometer range. In a nutshell, these advanced materials exhibit enhanced thermal, mechanical, barrier, and fire retardant properties over virgin polymers [32-37], while their performance depends on the level and the homogeneity of nanofillers dispersion, as well as on the potential for interfacial bonding between the filler and the matrix. 

Although still a relatively new area of development, the polymer nanocomposites show great promise as fire retardant materials. Not only can the combustion properties of the materials be modified but in many cases the mechanical properties are also improved [186, 187]. In such product with about 3% clay, the RHR decreases 20-60%, depending on polymer matrix without affecting at this loading the mechanical properties [188]. 

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