Antimony-halogen synergism

There is good experimental evidence for this mechanism of antimony-halogen synergism, most significantly that flame extinction time is a minimum for polymers containing antimony and halogen in the mole ratio 1 3. 

Zanetti, M. Camino, G. Canavese, D. Morgan, A.B. Lamelas, F.J. Wilkie, C.A. Fire retardant halogen-antimony-clay synergism in polypropylene layered silicate nanocomposites. Chem. Mater. 2002, 14, 189-193. 

Phosphorus compounds should be added to an extent of 1.5 to 2 per cent of phosphorus content in the foam. Above this level, no further flammability reduction is gained. Even 1 per cent of phosphorus is satisfactory in the presence of 10 to 15 per cent of chlorine, and in fact, the phosphorus level can be decreased to 0.5 per cent at 4 to 7 per cent content of bromine. Halogen-containing polyurethane foams are preferably supplemented with antimony trioxide synergent. 

The higher oxides of antimony (Sb204 and Sb20s) are somewhat weaker in synergism with halogens. Their consumption is still growing since Sb205, produced as a superfine colloid, is suitable for translucent or near-transparent materials. 

For these reasons, mainly additive flame-retardants are admixed with polyolefins. In most cases, the halogen/antimony synergism is utilized, selecting chlorinated paraffins or brominated aromatics as halogen sources. 

Not only halogen/antimony synergism but also other synergistic elfects have been observed in polystyrene, such as the mixture of halogenated organics with free-radical sources (essentially peroxides) which is especially useful for foams. 

Borates represent a novel opportunity for synergism with both brominated and non-halogenated flame retardant products. Although known for many years, their time has now, perhaps, arrived as antimony trioxide has come under a cloud. For instance, to capitalise on this opportunity Albemarle, the leading BFR company, is collaborating with US Borax to develop new borate-related technologies. 

Phosphorus compounds Reduced smoke obscuration and corrosivity development of halogen/phosphorus synergism could lead to wider use as a substitute for antimony oxide. Halogen-free phosphorus compounds are expected to boost sales in volume and value. 

The reduction of smoke obscuration and corrosivity favour this group of flame-retardant chemicals, especially in the US market, while market penetration is broadened by their use as alternative compounds to complement standard halogenated products. Further development of halogen/phosphorus synergism could lead to wider use as a substitute for antimony oxide. High value-added, halogen-free phosphorus compounds are expected to boost sales in volume and value. 

Antimony trioxide is a white powder, dusty imless oil-treated or pelletized. It remains solid at all polymer-processing temperatures. The synergism with halogen results from thermal formation of SbCla or SbBra, which inhibit flame by scavenging hydrogen atoms and other radicals. 

In halogen-containing polymers, the zinc borate can either partially or completely replace antimony oxide as a fire retardant synergist of halogen sources. The combination of antimony oxide and zinc borate can provide not only cost savings but also synergism in fire test performances (Figure 2). In addition, in contrast to antimony oxide, the zinc borate also... 

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