Retarding mechanism

Flame-retardant additives are capable of significant reduction in the ha2ard from unwanted fires, and techniques are now available to quantify these improvements. Combined with an understanding of fire-retardant mechanisms, polymer-retardant interactions, and reuse technology, formulations optimi2ed for pubHc benefit and manufacturing practicaUty can be selected. 

The shape of the curves is of some interest. An induction period is noted during which no oxygen uptake, i.e. oxidation, is observed. At the end of this induction period, when in effect antioxidant moieties have been consumed, oxygen uptake is rapid unless some retardation mechanism is at work. 

Ferry showed that superposition required that there be no change in the relaxation/retardation mechanism with temperature and that the T values for all mechanisms must change identically with temperature. Defining the ratio of any relaxation time Tat some temperature Fto that at reference temperature T0 as aT,... 

Melamine and its salts are widely used in formulations of fire retardant additives, particularly of the intumescent type (4-71. The role played by melamine structures in these additives is however not yet understood. The thermal behaviour is of paramount importance in studies of the fire retardance mechanism. It is known that melamine undergoes progressive condensation on heating with elimination of ammonia and formation of polymeric products named "melam", "melem", "melon" (8.91. The following schematic reaction is reported in the literature (10-121 ... 

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,... 

Chen, F., Burns, P. C. Ewing, R. C. 1999. 79Se geochemical and crystallo-chemical retardation mechanisms. Journal of Nuclear Materials, 275, 81-94. 

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. 

The fire-retardant mechanisms identified for the various phosphorus moieties in these polymethylmethacrylate (PMMA) and PS copolymers investigated can be summarized as follows ... 

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). 

These systems are of great importance in spite of the current cautious attitude, which will be discussed below, toward the use of halogen-based systems. Recent mechanistic results show that the active species formed by halogen compounds in the condensed phase may play a fundamental role in the hre-retardant mechanism, which could be reproduced using halogen-free moieties. 

Camino, G. Costa, L. Luda, M. P. Overview of fire retardant mechanism, Polymer Degradation and Stability, 1991, 33(2), 131-154. 

Kaspersma, J. Doumen, C. Munro, S. Prins, A. M. Fire retardant mechanism of aliphatic bromine compounds in polystyrene and polypropylene, Polymer Degradation and Stability, 2002, 77(2), 325-331. 

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. 

Their fire-retardant mechanism is predominantly due to condensed phase action involving a combination of endothermic decomposition, water release, and oxide residue formation. 

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. 

---