Nanocomposite intumescent

Pagella, C., Samyn, F., and Bourbigot, S. 2008. Laboratory scale testing of nanocomposite intumescent coating. Paper presented at 19th BCC Conference—Recent Advances in Flame Retardancy of Polymeric Materials, Stamford, CT, USA. 

Tang et al.84,85 also examined the incorporation of MMT in intumescent PP with a compatibilizer (hexadecyltrimethylammonium bromide) which is usually used as surfactant for making OMMT. Evidence of making a nanocomposite is shown with and without the intumescent system. Cone calorimetry shows a large improvement in the flammability properties when using OMMT. The results are similar to what we showed above. They postulated a mechanism of action suggesting the formation of an aluminophosphate structure but no evidence was given. 

In this chapter, we have discussed recent developments of intumescent flame-retarded materials in terms of reaction and resistance to fire. Research work in intumescence is very active. New molecules (commercial molecules and new concepts) have appeared. Nanocomposites are a relatively new technology in the held of flame retardancy. This technology gives the best results combined with conventional FRs and leads to synergistic effects with intumescent systems. Very promising developments in the synergy aspects are then expected and efforts should be continued in this way. 

Tang, Y., Hu, Y., Wang, Y.S., Gui, Z., Chen Z., and Fan, W. 2003. Intumescent flame retardant-montmorillonite synergism in polypropylene-layered silicate nanocomposites. Polym. Inter. 52 1396-1400. 

X-ray diffraction (XRD) has been poorly used to characterize the carbon phase of intumescent structure. Indeed, as shown previously, the carbon structure resulting from the development of the intumescent system is mainly disordered whereas XRD characterizes ordered structure. However, this technique may be of interest to study the carbonization process in the case of flame-retardant systems containing layered additives, such as expandable graphite,28,42 or even more in the case of lamellar nanocomposites, such as MMT-based nanocomposites. 

Bourbigot, S., LeBras, M., Dabrowski, F., Gilman, J., and Kashiwagi, T. 2000. PA-6 clay nanocomposite hybrid as char forming agent in intumescent formulation. Fire and Materials 24 201-208. 

Since the majority of research carried out on flame retardancy of nanocomposite has dealt with OMLS, the most investigated combinations have concerned the corresponding class of nanocomposites of polymers, particularly EVA copolymer, PP, and polystyrene. The great interest taken in the development of IFR systems has also entailed the development of various and complex compositions in which OMLS have been associated with different intumescent systems containing APP and co-synergists able to promote the formation of a stable and expanded char layer reinforced by aluminophosphate species formed by reaction between APP and OMLS. 

S. Bourbigot and S. Duquesne, Intumescence and nanocomposites A novel route for flame-retarding polymeric materials, in Flame Retardant Polymer Nanocomposites, A.B. Morgan and C.A. Wilkie (Eds.), Wiley Interscience, Hoboken, NJ, 2007, pp. 131-162. 

S. Bourbigot, M. Le Bras, F. Dabrowski, J.W. Gilman, and T. Kashiwagi, PA6 clay nanocomposite hybrid as char forming agent in intumescent formulations, Fire Mater., 2000, 24 201-208. 

The same method is applicable to control critical temperature where the reaction between polyphosphates and polyols takes place. For example, melamine polyphosphate-polyol system, which is stable at the degradation temperature of PP, has been activated for application in polyolefins [47], An activating effect is ascribed also to the char-forming polymers in intumescent nanocomposites, according to the blending approach [48],... 

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. 

Zhang et al. [31] studied fire-retardant properties of PP/IFR/LDH nanocomposites, which were comprised by a typical intumescent flame retardant (IFR) system and LDHs with different bivalent metal cations. The results of pk-HRR, pk-MLR, pk-EHC, and ignition time (IT) obtained from the cone calorimeter tests of various samples were listed in Table 8.1 [31]. It could been seen from Table 8.1 that the IT values of PP/IFR/LDH samples with different divalent metal cations of Zn, Mg, Cu, and Ca were 55, 55, 54, and 52 s, respectively, which are longer than 48 s of the PP/IFR sample without LDH. These data showed that the PP/IFR samples with LDHs are obviously harder to ignite than the sample only with the IFR. 

CNTs improve the flame retardancy of PP [36-38]. Figure 9.2 shows the heat release rates of PP and two nanocomposites. The peak heat release rate (PHRR) of PP was reduced by 73% by the addition of 1 vol% of MWCNTs. Although all samples burned nearly completely, the two nanocomposites burned much slower than PP. Further improvement on flame retardancy was achieved by the functionalization of CNTs with intumescent flame retardant (IFR) [38]. At the same CNTs content of 1 wt%, the PHRR of PP was reduced by 68% using pristine CNTs, and by 75% using IFR-functionalized CNTs. It was suggested that CNTs... 

Flame retardant intumescent formulations have been developed using charring polymers PA6, thermoplastic polyurethanes (TPUs), and hybrid clay-PA6 nanocomposites as carbonisation agents. The advantage of the eoncept is to obtain FR polymers with improved mechanical properties and to avoid the problem of migration and solubility of the additives. 

Other amide containing formulations can provide useful improvements to the meehanieal as well as fire properties of EVA compounds. These new intumescent formulations use PA6 and a PA6 elay nanocomposite hybrid as carbonisation agents. Work in both Franee and the US has shown that the clay allows the thermal stabilisation of a phosphoro-carbonaceous stmcture in the intumescent ehar which increase the efficiency of the shield and, in addition, the formation of a ceramie that can act as a protective layer. 

Wang ZY, Han EH, Ke W. Fire-resistant effect of nanoclay on intumescent nanocomposite coatings. J Appl Polym Sci February 2007 103(3) 1681-9. 

Y. Hu, Y. Tang, J. Xiao, J. Wang, L. Song, and W. Fan, PA-6 and EVA alloy/clay nanocomposites as char forming agents in poly(propylene) intumescent formulations. 

H. Y. Ma, L. F. Tong, Z. B. Xu, and Z. P. Fang, Functionalizing carbon nanotubes by grafting on intumescent flame retardant Nanocomposite synthesis, morphology, rheology, and flammability. Advanced Functional Materials, 18 (2008), 414-21. 

M. Zhang, P. Ding, and B. J. Qu, Flammable, thermal, and mechanical properties of intumescent flame retardant PP/LDH nanocomposites with different divdent cations. Polymer Composites, 30 (2009), 1000-1006. 

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