Fire-Retardant Mechanism

Although much work has been carried out on the mode of action of flame retardants generally, the mechanisms associated with tin additives are only partially understood. It is clear that tin-based fire retardants can exert their action in both the condensed and vapor phases, and that the precise action in any particular system depends on a number of factors, including incorporation level, the amount and chemical nature of other additives present, and the nature of the polymer itself. 

Thermal analysis experiments have clearly shown that tin-based fire retardants markedly alter both the initial pyrolysis and the oxidative burn off stages that occur during polymer breakdown These changes have been interpreted as being indicative of an extensive condensed phase action for the tin additive, in which the thermal breakdown of the polymer is altered to give increased formation of a thermally stable carbonaceous char at the expense of volatile, flammable products. The consequent reduction in the amount of fuel supplied to the flame largely accounts for the beneficial smoke-suppressant properties associated with zinc stannates and other tin-based fire retardants. 

Compound Boiling point (°C) Compou nd Boiling point (°C) 

In line with these observations, earlier Sn Mossbauer spectroscopic studies of rigid PVC samples containing Sn02 as a fire-retardant additive have shown that Sn(IV) is partially reduced to Sn(II) species (SnCl2 and SnO) and even to metallic tin during thermal degradation and combustion processes.In this case, the relatively involatile SnCb is detected in the char residue, whereas highly volatile SnCU is not. 

The fire-retardant mechanism associated with nanoclays has recently been studied and is likely to involve the formation of a ceramic skin which catalyzes char formation by thermal dehydrogenation of the host polymer to produce a conjugated polyene structure. The nanocomposite structure present in the resulting char appears to enhance the performance of the char through reinforcement of the char layer. These effects would explain the apparent fire-retardant synergy observed when nanoclays are incorporated into polymer formulations containing condensed phase fire-retardant systems, including coated fillers. 

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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. 

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

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. 

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

FIRE RETARDANCY MECHANISM OF BORON COMPOUNDS 9.3.1 Borates in Wood/Cellulose... 

Pawlowski, K. and Schartel, B. 2007. Fire retardant mechanisms of BDP in PC/ABS. Fire Retardancy and Protection of Materials (FRPM), Germany. 

B. Schartel, M. Bartholmai, and U. Knoll, Some comments on the main fire retardancy mechanisms in polymer nanocomposites, Polym. Adv. Technol., 2006, 17 772-777. 

Understanding Fire Behavior and Fire Retardancy Mechanisms.405... 

UNDERSTANDING FIRE BEHAVIOR AND FIRE RETARDANCY MECHANISMS... 

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. 

Camino G, Costa L, Luda di Cortemiglia MP. Overview of fire retardant mechanisms. Polym. Degrad. Stab. 1991 33 131-154. 

Fire retardance mechanisms of red phosphorus in thermoplastics. Proc. of the Additives 2003 Conference, San Francisco, CA, USA, April 6-9, 2003. 

A condensed phase fire retardant mechanism is proposed for APP in nylon-6 [141]. In fact, an intumescent layer is formed on the surface of burning nylon-6/APP formulations which tends to increasing content of APP. 

In epoxy resin, the combination of ATH and phosphonium-modified clay additives showed superposition or even synergetic behavior for nearly all fire retardancy properties. Schartel et al. suggested that the presence of ATH resulted in an increase in residues and a small decrease in effective heat of combustion because of dilution of the pyrolysis products [24], Both fire retardancy mechanisms have their primary source in the conversion of ATH into aluminum oxide, which increased the residues, and water, which diluted and cooled the flame zone. In addition, the presence of organophosphorus decreased the effective heat of combustion through a gas phase. Most of the phosphorus was liberated during polymer pyrolysis and influenced the Are behavior through flame inhibition. 

Keywords tin, tin oxide, zinc hydroxystannate, zinc stannate, organotin compounds, antimony trioxide, alumina trihydrate, magnesium hydroxide, titanium dioxide, molybdenum trioxide, iron oxide, zinc borate, alumina, halogenated flame retardants, metal halides, thermal analysis, Mossbauer spectroscopy, fire-retardant mechanism, ultrafine powders, coated fillers. 

CONSIDERATIONS REGARDING SPECIFIC IMPACTS OF THE PRINCIPAL FIRE RETARDANCY MECHANISMS IN NANOCOMPOSITES... 

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