Chlorine-Containing Flame Retardants

The use of chlorinated additives as flame retardants is often in conjunction with other materials such as phosphorus or antimony-containing additives. The choice of a chlorinated additive depends on the stability of the material, the volatility, chlorine content, and kinetics of reaction in the gas phase during combustion. The use of such materials, however, is decreasing owing to the toxicity of polychlorinated biphenyls (PCBs) and products with related molecular structures. 

Examples of chlorinated additives include chlorinated paraffins derived from chlorination of petroleum distillates and represented by the general formula 

Material CAS no. MW Br content (%) Melting point (°C) Advantages Application 

Trisbromoneopentyl alcohol 36483-57-5 325 73 65 Low leaching, heat stability Polyurethanes 

Hexabromocyclo-dodecane 25637-99-4 642 73 180 transparency High purity and efficiency EPS, XPS 

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Chlorine-containing flame retardants can be divided into three groups aliphatic, alicyclic (cycloaliphatic), and aromatic. Their thermostability is increased in this order, bnt flame retardant efficiency is decreased in the same order. This reciprocal tendency is common among flame retardants. Clearly, the higher the thermal stability, the higher the temperatnre at which the flame retardant becomes chemically active and fnnctional as a flame retardant. 

A common disadvantage of chlorine-containing flame retardants is that they have to be added in quantities, which in turn decrease mechanical properties of the polymer materials. The same sitnation in terms of large amount that should be added into the base material holds for mineral flame retardants as well (ATH, Mg(OH)2) however, minerals typically improve both flexural modulus (stiffness) and flexural strength of composites. 

Brominated dimethyisulphone dialkyl ether Bromine/chlorine containing flame-retardant Blend aromatic bromine, aliphatic chlorine... 

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. 

Antimony oxide by itself is essentially useless as a fire-retardant additive. However, in combination with other materials, it is by far the most widely used antimony-containing flame retardant additive. It is generally used with bromine- or chlorine-containing compounds (32). 

Metal hydrates such as aluminium trihydrate or magnesium hydroxide remove heat by using it to evaporate water in their structures, thus protecting polymers. Bromine or chlorine-containing fire retardants interfere with the reactions in flames and quench them. Mixtures of flame retardants antimony trioxide and organic bromine compounds are more effective at slowing the rate of burning than the individual flame retardants alone. 

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]. 

The newer families of polymeric or oligomeric or reacted-in bromine, as well as very high molecular weight chlorine- or bromine-containing flame retardants are well designed to avoid migration and to be innocuous environmentally, since they have essentially no water solubility or vapor pressure. 

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. 

Alnminnm hydroxide (also known as alumina trihydrate) Bromine-containing flame retardant Chlorinated paraffin wax Decabromodiphenyl oxide... 

Molybdenum trioxide is a condensed-phase flame retardant (26). Its decomposition products ate nonvolatile and tend to increase chat yields. Two parts of molybdic oxide added to flexible poly(vinyl chloride) that contains 30 parts of plasticizer have been shown to increase the chat yield from 9.9 to 23.5%. Ninety percent of the molybdenum was recovered from the chat after the sample was burned. A reaction between the flame retardant and the chlorine to form M0O2 012 H20, a nonvolatile compound, was assumed. This compound was assumed to promote chat formation (26,27). 

Cblorina.ted Pa.ra.ffins, The term chlotinated paraffins covers a variety of compositions. The prime variables are molecular weight of the starting paraffin and the chlorine content of the final product. Typical products contain from 12—24 carbons and from 40—70 wt % chlorine. Liquid chlotinated paraffins are used as plasticizers (qv) and flame retardants ia paint (qv) and PVC formulations. The soHd materials are used as additive flame retardants ia a variety of thermoplastics. In this use, they are combiaed with antimony oxide which acts as a synergist. Thermal stabilizers, such as those used ia PVC (see vinyl polymers), must be used to overcome the inherent thermal iastabiUty. 

Flame Retardants. Because PVC contains nearly half its weight of chlorine, it is inherently flame-retardant. Not only is chlorine not a fuel, but it acts chemically to inhibit the fast oxidation in the gas phase in a flame. When PVC is diluted with combustible materials, the compound combustibiHty is also increased. Por example, plastici2ed PVC with > 30% plastici2er may require a flame retardant such as antimony oxide, a phosphate-type plastici2er, or chlorinated or brominated hydrocarbons (145,146). 

Flame Retardants. Most polymers, because they are organic materials, are flammable. Additives that contain chlorine, bromine, phosphorous or metallic salts reduce the likelihood that combustion will occur or spread. 

The use of aromatic brominated compounds as flame retardants has been a potential source of environmental contamination. Incomplete incineration of these compounds and wastes (plastics, textiles, oils etc...) containing brominated flame retardants caused formation of brominated/chlorinated dibenzodioxines (PBDDs/ PCDDs) and dibenzofurans (PCDFs/PBDFs) (refs. 1 - 4). 

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