Halogenated chlorine-containing flame retardants

Halogen-containing flame-retardants such as chlorinated paraffins, poly-bromodiphenyl oxides, and polybromodiphenyls are used in conjunction with antimony oxide. On exposure to fire, the halogen gases hberated by decomposition of the resin component of the paint film react with the antimony oxide to produce a vapor of antimony hahde that blankets the flame. 

Despite some environmental concerns, halogenated flame retardants still play an important role. With the exception of a few chlorinated products (e.g., chlorinated paraffins), these flame retardants contain usually molecules with several bromo groups (Fig. 11.18). Bromo compounds are active during combustion in the gas phase, whereas HBr reacts with OH and H radicals under formation of less reactive halogen radicals. The flame retardancy of bromo compounds is often synergistically improved by the addition of antimony oxide Sb203. 

Phosphorus containing flame retardants are used as phosphates, phosphonates, phosphines and phosphinic oxides. Halogen-containing phosphate esters such as bromine and chlorine in the form of tris (halogen alkyl) phosphates are popular [33]. The effects of phosphorus and brominated additives on flexible PU foam were compared [179]. Melamine has broad utility as a flame retardant additive in flexible PU foams [180]. 

Although solder masks do not typically contain flame retardants, and hence no bromine, they often contain chlorine. The chlorine generally comes from pigments that give the mask its desired color, and also from residual catalyst from the resin (solder mask raw material) manufacturing process. A number of manufacturers offer low-halogen solder mask materiak that meet the specified criteria. 

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. 

The order of effectiveness of halogens is I > Br > Cl > F [20]. Iodine-containing organic compounds are too thermally unstable to be melt compounded with polystyrene, and organoflorine comounds are too thermally stable to be effective as flame retardants. This leaves bromine- and chlorine-containing compounds as the most effective flame retardants. 

Halogenated phosphate esters (26) and many other types of flame retardants such as phosphorous-containing compounds including chlorine and/or bromine were extensively reviewed by Hilado (154). 

Fire resistant PU are obtained by the addition or by introduction into the PU structure of special compounds, called flame retardants. The flame retardants are organic compounds containing halogens (chlorine, bromine) and phosphorus. Compounds of antimony (Sb) or boron [1-13] are rarely used. Sometimes inorganic compounds are used as flame retardants for PU, such as, hydrated alumina (Al203 nH20), Sb203 or ammonium polyphosphate [1-3, 14]. 

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