Flame retardation mechanisms

The flame retardant mechanism for phosphorus compounds varies with the phosphorus compound, the polymer and the combustion conditions (5). For example, some phosphorus compounds decompose to phosphoric acids and polyphosphates. A viscous surface glass forms and shields the polymer from the flame. If the phosphoric acid reacts with the polymer, e.g., to form a phosphate ester with subsequent decomposition, a dense surface char may form. These coatings serve as a physical barrier to heat transfer from the flame to the polymer and to diffusion of gases in other words, fuel (the polymer) is isolated from heat and oxygen. 

Condensed-phase flame retardant mechanisms, 44 484—485 Condensed phosphates, 18 841-852 colloidal properties of, 48 851 complex ion formation in,... 

The flame retardant mechanism of PC/ABS compositions using bisphenol A bis(diphenyl phosphate) (BDP) and zinc borate have been investigated (54). BDP affects the decomposition of PC/ABS and acts as a flame retardant in both the gas and the condensed phase. The pyrolysis was studied by thermogravimetry coupled with fourier transform infrared spectroscopy (FUR) and nuclear magnetic-resonance spectroscopy. Zinc borate effects an additional hydrolysis of the PC and contributes to a borate network on the residue. 

Blends of iso- and terephthalates give amorphous, transparent resins, mosdy yellow in color. Heat-deflection temperatures are higher than those of 100% PC resins and depend on the iso- to terephthalate ratio. For example, a resin with a 1 1 ratio has a value of 160°C. These resins are flame retardant mechanical and electrical properties are similar to those of PC resins. The notched Izod impacts are lower at 150—300 J/m (4.7—5.6 fflbf/in.), even in thick sections. Long-term uv radiation stabilities are excellent, but yellowness increases during initial exposure owing to photo-Fries rearrangements (80), wherein 0-hydroxy-benzophenone units are produced along the polymer chains. 

J. Zhang, A.R. Horrocks, and M.E. Hall, Flammability of polyacrylonitrile and its copolymers. III. The flame retardant mechanism of ammonium polyphosphate. Fire Mater., 18, 307-312 (1994). 

FIGURE 6.14 Flame retardancy mechanism of FR PET fabrics treated with PPPBP. (From Liu, W. et al., Polym. Deg. Stab., 92, 1046, 2007.)... 

Braun, U., Schartel, B., Fichera, M.A., and Jaeger, C. 2007. Flame retardancy mechanisms of aluminium phosphinate in combination with melamine polyphosphate and zinc borate in glass-fibre reinforced polyamide 6,6. Polym. Deg. Stab. 92 1528-1545. 

Hermansson, A., Hjertberg, T., and Sultan, B.-A. 2003. The flame retardant mechanism of polyolefins modified with chalk and silicone elastomer. Fire Mater. 27 51-70. 

Marosi, G., Keszei, S., Marton, A., Szep, A., Le Bras, M., Delobel, R., and Hornsby, P. Flame retardant mechanisms facilitating safety in transportation. In Fire Retardancy of Polymers New Applications of Mineral Fillers, M. Le Bras, C.A. Wilkie, S. Bourbigot, S. Duquesne, and C. Jama (Eds.), pp. 347-360. Cambridge, U.K. The Royal Society of Chemistry. 

The reactive approach has been employed recently to prepare various polymeric systems.34 35 Silicon-containing polystyrenes and poly(methyl methacrylate)s (PMMAs) copolymers have been prepared by free radical polymerization. The LOI data indicated that a marginal improvement in flame retardancy has been observed compared to the parent homopolymers. The authors speculated that the nature of the silicon-containing group has an effect on the flame-retardant mechanism.34... 

Gilman, J.W., Kashiwagi, T., Nyden, M., and Harris, R.H., New flame retardants consortium Final report, Flame retardant mechanism of silica, NISTIR 6357, June 1999. 

Fu, M. and Baojun, Q., Synergistic flame retardant mechanism of fumed silica in ethylene-vinyl acetate/ magnesium hydroxide blends, Polym. Degrad. Stab. 2004, 85, 633. 

Qu, B. and Xie, R. 2003. Intumescent char structures and flame-retardant mechanism of expandable graphite-based halogen-free flame-retardant linear low density polyethylene blends. Polymer International 52(9) 1415-1422. 

J.W. Gilman, Flame retardant mechanism of polymer-clay nanocomposites, in Flame Retardant Polymer Nanocomposites, A. Morgan and C. Wilkie (Eds.), Wiley-Interscience, Hoboken, NJ, 2007, p. 67. 

L. Ye and B. Qu, Flammability characteristics and flame retardant mechanism of phosphate-intercalated hydrotalcite in halogen-free flame retardant EVA blends, Polym. Degrad. Stabil., 2008, 93 918-924. 

It is concluded that the difference in flame retardancy mechanisms of phosphorous flame retardants is due to the different decomposition pathways and interactions between flame retardant and polymer or their decomposition products, respectively. The release of phosphorous-containing molecules into the gas phase competes with char-inducing or inorganic residue-forming interactions... 

Combining data obtained by the cone calorimeter with pyrolysis combustion flow calorimeter (PCFC sometimes called microscale combustion calorimeter, MCC) results was also proposed to increase the understanding of flame retardancy and flame retardancy mechanisms.104 Dividing the fraction of the effective heat of combustion of the volatiles (THE/ML) obtained from the cone calorimeter by the heat of complete combustion of the volatiles obtained from PCFC yields the combustion efficiency %. Thus the combination of fire test and PCFC enables a quantitative... 

Flame retardants or flame retardancy mechanisms, respectively, influence different fire properties quite differently, and, what is more, show different effectiveness in different fire scenarios, and thus fire tests. In extreme cases, flame retardancy with respect to a specific fire property or specific test is achieved with little or no improvement in performance in another fire property or fire test. This fundamental understanding in fire science sometimes may be overlooked in materials development, but is worth addressing. The influence on different fire risks and the dependency of effectiveness on the scenario addressed is discussed subsequently based on the fire retardancy mechanisms accompanying charring and barrier formation. 

Braun U, Schartel B. Flame retardant mechanisms of red phosphorus and magnesium hydroxide in high impact polystyrene. Macromol. Chem. Phys. 2004 205 2185-2196. 

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