Flame halogenated fire retardants

The traditional halogen fire retardants used in styrenic copolymers are decabromodiphenyl ether and octabromodiphenyl ether, tetrabromobisphenol A, bis(tribromophenoxy) ethane, ethylene bis-tetrabromophthalimide, and chlorinated paraffins. Actually the octabromodiphenyl ether has been banned on precautionary principles, as will be explained below. The fire-retardant capabilities of the more effective halogen-containing compounds are in line with the quantity of halogen in the final polymer blend, with consideration for the use of synergists. Thus, the practical utility of these flame-retardant compounds (once the issue of degradation temperature is resolved) is often based on their ability to be blended into the polymer and to not substantially affect the physical properties of the polymers. 

Thermoset composites are mainly considered due to their intrinsic fire resistance. They provide low flame spread and very low smoke emissions without any addition of halogenated fire retardants or higher loading of filler or reinforcing materials. Phenol-formaldehyde and urea-formaldehyde are the most common thermosetting resins used as adhesives for wood composite products, including plywood, particleboard, fibreboard and oriented strand board [66-69]. 

The advantage of this approaeh is the possibility to reaeh a desirable flame retardant effeet with a lower amount of halogenated compound. Moreover, the addition of metal oxides, sueh as AO, to halogenated fire retardants increases their effieieney through the formation of antimony trihalide, a volatile product that slows reactions in the flame, even tiiough the oxide itself has no effect. In... 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

Antimony trioxide and chlorinated paraffinic derivatives are common materials used as fire retardants, as are intumescent zinc (or calcium) borate, aluminium hydroxide and magnesium hydroxide. These inorganic materials, used as bulk fillers, act to reduce the fire hazard. Halogenated materials release chlorine, which then combines with the antimony trioxide to form the trichloride, which is a flame suppressant. 

J,W. Hastie and C.L. McBee, "Mechanistic Studies of Halogenated Flame Retardants The Antimony-Halogen Systems,"in Halogenated Fire Suppressants, R.G. 

Flame retardants, 11 447-454, 459-479. See also Fire retardant entries Halogenated flame retardants Phosphorus flame retardants antimony compounds in, 3 54 brominated and chlorinated additive, 11 461-470... 

Suitable fire retardant materials include halogen compounds in combination with antimony compounds, including, tetrabromobis-phenol A and antimony trioxide. Examples for halogen free flame retardants are phosphate esters, such as Hoechst Celanese AP422 or Hoechst Celanese IFR 23. 

Cables are available in a variety of constructions and materials, in order to meet the requirements of industry specifications and the physical environment. For indoor usage, such as for Local Area Networks (LAN), the codes require that the cables should pass very strict fire and smoke release specifications. In these cases, highly flame retardant and low smoke materials are used, based on halogenated polymers such as duorinated ethylene—propylene polymers (like PTFE or FEP) or poly(vinyl chloride) (PVC). For outdoor usage, where fire retardancy is not an issue, polyethylene can be used at a lower cost. 

The mechanism of action of an effective fire retardant acting in the vapor phase should inhibit one or both reactions (Equation 4.2 and Equation 4.3) because they have a paramount effect on the increase of the overall rate of thermal oxidation process occurring in the flame. Indeed, the reaction represented by Equation 4.2 increases radical concentration while reaction represented by Equation 4.3 increases the temperature. From a mass spectrometry study of species sampled in low-pressure flame,4 it is evident that the introduction of halogen species into a premixed CH4/02 flame leads to the production of the hydrogen halide, HX, early in the flame. It was also observed that the production of H2 is enhanced. This provides evidence for removal of H atoms from the flame and the predominant reaction is considered to be... 

Larsen, E. R. Mechanism of flame inhibition. I The role of halogens, Journal of Fire and Flammability/ Fire Retardant Chemistry, 1974, 1, 4—12. 

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