Fire behavior of nanocomposites

An important factor in study of thermal stability of synthetic mbber nanocomposites is the dispersion of the nanoparticle on the matrix. The presence of nanoparticles exfoliated influences the thermal or fire behavior of nanocomposite [83]. 

Recently, new approaches on flame retardancy deal often with nanofillers and in this section some examples of improvements of fire behavior of polymeric foams obtained by use of nanoclays or nanofibers will be shown. Much more details on flame retardancy of polymeric nanocomposite may be found elsewhere as for example in the book edited by A. B. Morgan and C. A. Wilkie105 or in scientific review.106 Polymer nanocomposites have enhanced char formation and showed significant decrease of PHRR and peak of mass loss rate (PMLR). In most cases the carbonaceous char yield was limited to few weight %, due to the low level of clays addition, and consequently the total HRR was not affected significantly. Hence, for polymer nanocomposites alone, where no additional flame-retardant is used, once the nanocomposite ignites, it burns slowly but does not self-extinguish... 

Schartel B, Braun U, Knoll U, Bartholmai M, Goering H, Neubert D and Potschke P (2008) Mechanical, thermal, and fire behavior of bisphenol a polycarbonate/multiwall carbon nanotube nanocomposites, Polym Eng Sci 48 149-158. 

Study [25] concluded that this fire performance is probably due to filler-induced increased char formation, because the reductions in PHRR are roughly comparable for all four composites, despite their morphological variations (ranging from very good nanoscale and mesoscale dispersions for the MMT-based nanocomposites to rather poor dispersions and conventional composite structures for the magadiite-based composites [25]). In addition, when the fire behavior of these PET nanocomposites [25] was compared with that of PS nanocomposites [47] (based on both alkylquinolinium- and alkylammonium-modified MMT), it was suggested that the thermally stable quinolinium surfactants are more effective in fire-resistance improvement than the alkylammonium surfactants [25]. 

Modesti, M., A. Lorenzetti, S. Besco, D. Hreja, S. Semenzato, R. Bertani, and R. A. Michelin. 2008. Synergism between flame retardant and modified layered silicate on thermal stability and fire behavior of polyurethane-nanocomposite foams. Polym. Deg. Stab. 93 2166-2171. 

The impact of the nanocomposite technology on polymers is huge, reflected in enhanced properties of the resulting PNs, such as enhanced mechanical, barrier, solvent-resistant, and ablation properties.12 The effect of nanocomposite technology on the thermal and fire performance of the polymers is primarily observed in two important parameters of the polymers (1) the onset temperature (7( ,nsct) in the thermogravimetric analysis (TGA) curve—representative of the thermal stability of the polymer, and (2) the peak heat release rate (peak HRR) in cone calorimetric analysis (CCA)—a reflection of the combustion behavior (the flammability) of the polymer. The Tonset will be increased and the peak HRR will be reduced for a variety of polymers when nanoscale dispersion of the nanoadditive is achieved in the polymer matrix. 

The impact of nanocomposite technology on flame retardance (the thermal and fire resistance) of the polymers, as mentioned in Section 11.1, is primarily reflected in two important parameters (1) the ronset in the TGA curve—representative of the thermal stability of the polymer and (2) the peak HRR in the curve of CCA—reflection of the combustion behavior (the flammability) of the... 

Jang, B. N., Costache, M., and Wilkie, C. A. The relationship between thermal degradation behavior of polymer and the fire retardancy of polymer/clay nanocomposites, Polymer (2005), 46, 10678-10687. 

FIGURE 24.10 Vertical burning behavior of (a) nylon 6 and (b) nylon 6 strings containing 8% 15A nanoclay. (From Ratnayaka, A., High performance fire retardant synthetic fibres incorporating nanocomposites, MSc thesis, University of Bolton, Bolton, U.K., May 2007.)... 

Fire retardancy behavior of PP/PA66 blends compatibilized with PP-g-MAH and modified with untreated and treated nanoclays was studied (Kouini and Serier 2012). It was found that the intercalation, exfoliation of nanoclays of nanocomposites, and the flame retardancy properties were improved significantly. In addition a good balance of impact strength and flame retardancy was obtained for PP/PA66 nanocomposites in the presence of PP-g-MA compatibilizer. The presence of the clay led to an increase in the flammability time. In addition, the treatment made a more pronounced effect. A 23 % increase was observed only when 4 wt% nanoclay was added and a longer flammabiUty time was noticed with treated clay. This was attributed to the stacking of nanoclay which created a physical protective barrier on the surface of the material. Similar behavior has been reported by earlier workers (Kocsis and Apostolov 2004). 

Montmorillonite (MMT), a smectite clay, is probably the most extensively studied nanomaterial in terms of mechanical, thermal, fire retardant or crystallization behavior of polylactide, especially when these nanoparticles are organically modified allowing the achievement of intercalated and exfoliated nanocomposites.These nanocomposites show enhanced properties as compared to microcomposites and pristine polymer. However, biodegradation and hydrolytic degradation of PLA in the presence of nanoclays has been investigated to a small extent. 

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