Nanoparticles, flame retardants carbon nanotubes

The different flame-retardant (FR) mechanisms of action of current nanoparticles, such as layered silicates, carbon nanotubes (CNTs), and nano-oxides or -hydroxides, according to their nature and interfacial modifications, are relatively well known and detailed in numerous works.5 13 These mechanisms are rather different from those exhibited by usual FRs and correspond mainly to the following physical, physicochemical, or chemical actions ... 

Combinations of Carbon Nanotubes with Flame Retardants and Nanoparticles... 

More recently nanoscale fillers such as clay platelets, silica, nano-calcium carbonate, titanium dioxide, and carbon nanotube nanoparticles have been used extensively to achieve reinforcement, improve barrier properties, flame retardancy and thermal stability, as well as synthesize electrically conductive composites. In contrast to micron-size fillers, the desired effects can be usually achieved through addihon of very small amounts (a few weight percent) of nanofillers [4]. For example, it has been reported that the addition of 5 wt% of nanoclays to a thermoplastic matrix provides the same degree of reinforcement as 20 wt% of talc [5]. The dispersion and/or exfoliahon of nanofillers have been identified as a critical factor in order to reach optimum performance. Techniques such as filler modification and matrix functionalization have been employed to facilitate the breakup of filler agglomerates and to improve their interactions with the polymeric matrix. 

The accumulation of clay at the surface acts thus as a barrier which limits heat transfers and reduces the release of combustible volatiles into the flame. A substantial decrease in the peak heat release rate of the nanocomposite (25 to 50%) can be achieved compared to the neat polymer (Bourbigot et al, 2006). However, this effect is very dependent on the quality of dispersion of the nanoparticles within the host matrix, and a high degree of exfoliation is usually targeted in order to maximize both the mechanical and fire properties (Hackman and Hollaway, 2006). Other types of nanoparticles, such as silica (Si02), titanium dioxide (Ti02), carbon nanotubes or silesquioxane, have also proven to have significant flame-retardant properties (Laoutid et al., 2009). 

A new class of materials, called nanocomposites, can avoid the disadvantages of traditional flame retardant systems. Generally, the term nanocomposite describes a two-phase material with a suitable nanofiller (organoclay, nanoparticles, carbon nanotubes, etc.) dispersed in the polymer matrix at the nanometric scale [3,4]. 

It is of interest to determine the flame retardant effectiveness of shapes or types of nanoparticles other than layered silicates, to find what shape or type of nanoparticle is most effective for improving the flammability properties of commodity polymers. In this chapter, flammability properties of nanocomposites containing nanoscale oxides such as nanoscale silica particles and metal oxides, polyhedral oligomeric silsesquioxanes (POSSs), and carbon-based nanoparticles such as graphite, single-walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes (MWNTs), and carbon nanofibers (CNFs) are described and a flame retardant mechanism of these nanoparticles is discussed. 

A trend that has already begun to arise is the use of multiple types of nanofillers in the same polymer to yield a multicomponent nanocomposite. Some workers have found that some types of nanofillers cannot bring all of the desired properties to the final material, so clays have been combined with multiwall carbon nanotubes to bring enhanced properties.The observation for most polymer additives is that they cannot be used for all applications in all polymers, and the same observation will surely be made about nanocomposites. A clay may be used to enhance the flammability performance, bnt it could also be combined with a conductive nanoflller to impart antistatic aspects or electrical conductivity in the final system. One potential way to look at the use of multiple nanoparticles is that each nanoparticle plays a complementary role in flammability reduction. For example, one could choose a clay for mass loss rate or fuel release reduction, but then use a colloidal particle to flu in the gaps between clay plates as the nanocomposite thermally decomposes. Perhaps even more useful, the colloidal particle could have catalytic or flame retardant properties that encourage... 

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