Flame retardant nanocomposites with polymer blends

Flame retardant nanocomposites with polymer blends 

The authors acknowledge the EU for financially supporting the PREDFIRE-NANO project under Grant 013998 in the sixth Framework Program. The authors thank J. Hereid, M. Hagan, and M. McKee for conducting the cone calorimeter experiments and Dr. V. Mittal for inviting us to write this contribution. 

Although there has been extensive research (e.g., [1-9]) on the fire retardation effects of nanoclay on neat polymers, relatively few studies [15-31] have been conducted with polymer blend systems. In Table 8.1, the polymer blends as well as the tests conducted in [ 15-31 ] are presented. From this table, it is clear that the majority of these studies have been devoted to the morphology and thermal stability of polymer blend nanocomposites very few studies actually focused on their fire performance. Nonetheless, these studies [15-31] have generally led to the conclusion that the addition of nanoclay to polymer blends can result in remarkable improvement in (a) mechanical properties, (b) compatibilization, (c) viscosity, (d) thermal stability, and (e) flammability. 

In this chapter, we present a summary of fire retardant nanoclays used in polymer blends based on the authors previous experience and the literature [15-31]. Because the main objective of this work is to study the fire retarding effects of nanoclays on polymer blends, we will focus on the properties affecting the fire performance of polymer blends (a) dispersion of nanoclay, (b) rheology, (c) thermal stability, and (d) flammability (ignition, fire spread, and toxicity), whereas the effects of nanoclays on mechanical properties and compatibilization can be found easily in references listed in Table 8.1 (e.g.. References [16, 17, 19-21] on compatibilization and [16, 18, 21, 25, 26, 29-31] on mechanical properties). A review of the mechanism by which nanoparticles organize in polymer blends is also available in [32]. 

This chapter is organized in the following way. First, we present some common techniques for characterizing the dispersion of nanoclays in polymer blends. The dispersion level has been shown to have a fundamental effect on the fire performance of polymer-clay nanocomposites (PCNs), as an exfoliated or intercalated polymer-clay system seems to enjoy reduced flammability. Second, the effects of nanoclays on the viscosity of polymer blends are discussed. With increased temperature in the condensed phase during combustion, most polymers (and hence polymer blends) have sufficiently low viscosity to flow under their own weight. This is highly undesirable, especially when the final products will be used in vertical orientation, because the melt can drip, having the potential to form a pool fire, which can increase fire spread. The results on thermal stability are presented next, followed by those for the cone calorimeter. The quantitative effects of nanoclays on the 

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Flame retardant nanocomposites with polymer blends... 

This is another important and widely used polymer. Nanocomposites have been prepared based on this rubber mostly for flame-retardancy behavior. Blends with acrylic functional polymer and maleic anhydride-grafted ethylene vinyl acetate (EVA) have also been used both with nanoclays and carbon nanotubes to prepare nanocomposites [65-69]. 

Jho et al. pointed out that modified montmorillonites alone are not sufficient as flame retardants used in cable applications. Also, Wilkie gave a clear statement It is apparent that nanocomposite formation alone is not the solution to the fire problem, but it may be a component of the solution. We, and others, have been investigating combinations of nanocomposites with conventional fire retardants. Charring polymers such as PA6 and PA6 nanocomposites were used by Bourbigot et al. to improve the flame retardancy of EVA. The organoclay increased the efficiency of the char as a protective barrier by thermal stabilization of a phosphorocarbonaceous structure in the intumescent char and additionally, the formation of a ceramic layer. Hu et al. used a blend of PA6 and EVA-nanocomposite to improve the flame retardancy of PP. 

It is concluded, therefore, that the combination of organoclay with oligomeric phosphate or bromine leads to an increase in thermal stability of both the modified clay and the corresponding polymer nanocomposite. The role of the flame retardant element is entirely different. The combination of a phosphate flame retardant with OMT enhances char formation. However, the addition of brominated flame retardant additives appears not to affect char formation. Thus, a general trend may not exist (i.e., in some cases bulk polymerization apparently gives enhanced thermal stability, whereas in others, melt blending may give a better result)." " ... 

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