Flame retardant compounds with antimony oxide

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). 

Because the alkane feedstock consists of n-alkanes with a range of chain lengths, the final preparation contains a mixture of their chlorinated analogues. PCA mixtures may be contaminated by isoparaffins, aromatic compounds, sulfur, metals, and unreacted n-alkanes [4, 5]. As the purity of tt-paraffin feedstocks has improved so to has the purity of the PCA products [11, 12]. Commercial products may contain additives added to inhibit decomposition of the PCA, via HCl loss, at elevated temperatures and to increase flame retardancy (e.g., antimony oxide). Common stabilizers include epoxides and organotin compounds [6]. The concentration of these additives, however, is usually below 0.05% [13],... 

Molybdenum Oxide. Molybdenum compounds incorporated into flexible PVC not only increase flame resistance, but also decrease smoke evolution. In Table 10 the effect of molybdenum oxide on the oxygen index of a flexible PVC containing 50 parts of a plasticizer is compared with antimony oxide. Antimony oxide is the superior synergist for flame retardancy but has Httle or no effect on smoke evolution. However, combinations of molybdenum oxide and antimony oxide may be used to reduce the total inorganic flame-retardant additive package, and obtain improved flame resistance and reduced smoke. 

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. 

As FAA flammability requirements have changed in the past, both epoxy and polyurethane materials have been reformulated to comply with new regulatory standards and individual OEM aircraft demands. For example, the first flame-retardant epoxies included halogenated compounds and antimony oxide to reduce flammability. However, the presence of bromines generated high levels of smoke, making the products inappropriate for many cabin interior applications. 

Zinc borate. Zinc borate is the major boron compoimd used as a flame retardant in plastics. It competes with antimony oxide when antimony prices are high. The largest application for boron compounds as a flame retardant is in cellulose insulation. The flame-retardant categories and the major plastics where they are used are summarized in Table 4.11. 

Antimony oxide works synergistically with reactive or additive halogenated compounds to improve the flame-retarding effect of the halogens so that less of the halogenated compound needs to be used, with consequently less effect on physical properties. Antimony oxide is effective when used in combination with such organic flame-retardant compounds as chlorinated paraffins, chlorinated cycloaliphatics, aromatic bromine compounds, alkyl chlorine, or bromine and phosphates. It is used in such resins as ABS, polyethylene, polypropylene, polystyrene, thermoplastic polyester (PBT), and unsaturated polyesters. 

Epoxy molding compounds are made flame retardant with tetrabromo-bisphenol A as the reactive intermediate in manufacturing the epoxy compound. Rigid polyvinyl chloride (PVC) usually does not require flame retardants because of its high chlorine content. However, flexible PVC will use retardants such as antimony oxide, zinc borate, and chlorinated paraffins and phosphate esters. ATH can also be used in compounds that tolerate fillers and is typically combined with antimony oxide and phosphate esters. 

Alloying different plastics with different flame retardant characteristics can also improve flame retardancy. A typical compound would be ABS-PVC alloys. Recently, PVC with antimony oxide has also been investigated for alloying with thermoplastic polyurethane. 

Chlorinated paraffins are claimed to be one of the lowest cost FRs besides the hydrated metal oxides. They can be used with antimony oxide as FRs in unsaturated polyester resin systems. Special grades have been developed by Dover Chemical in its Hordaresin and Chlorez ranges for flame retarding high-impact polystyrene, offering an absence of polyhalogenated biphenyls or dioxins, low cost, improved melt flow, and better UV stability than aromatic brominated FRs. They are also used in rubber compounds, where they can also improve tensile and tear properties of neoprene, SBR, and nitrile, and in EPDM rubber for electrical or roofing products. 

A free-flowing white powder, Dechlorane Plus contains 65 percent chlorine In a cycloaliphatic compound, ideal for imparting flame retardant properties to thermoplastics, thermosets and elastomers. As the only stable chlorinated flame retardant on the market, Dechlorane Plus is usually combined with antimony oxide (Sb203), but In some resins can be used with other synergists. 

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... 

In polymers such as polystyrene that do not readily undergo charring, phosphoms-based flame retardants tend to be less effective, and such polymers are often flame retarded by antimony—halogen combinations (see Styrene). However, even in such noncharring polymers, phosphoms additives exhibit some activity that suggests at least one other mode of action. Phosphoms compounds may produce a barrier layer of polyphosphoric acid on the burning polymer (4,5). Phosphoms-based flame retardants are more effective in styrenic polymers blended with a char-forming polymer such as polyphenylene oxide or polycarbonate. 

Antagonism between antimony oxide and phosphoms flame retardants has been reported in several polymer systems, and has been explained on the basis of phosphoms interfering with the formation or volatilization of antimony haUdes, perhaps by forming antimony phosphate (12,13). This phenomenon is also not universal, and depends on the relative amounts of antimony and phosphoms. Some useful commercial poly(vinyl chloride) (PVC) formulations have been described for antimony oxide and triaryl phosphates (42). Combinations of antimony oxide, halogen compounds, and phosphates have also been found useful in commercial flexible urethane foams (43). 

The tetramethylol derivative of DABT, prepared by reaction of DABT with alkaline aqueous formaldehyde, polymerized readily on cotton. It imparted excellent flame retardancy, very durable to laundering with carbonate- or phosphate-based detergents as well as to hypochlorite bleach. This was accomphshed at low add-on without use of phosphoms compounds or antimony(III) oxide (75—77). 

More recently, based on the results of an extensive series of small scale degradation studies, two additional mechanisms for the volatilization of antimony from antimony oxide/organohalogen flame retardant systems have been proposed (23,24). Of these two proposed mechanisms, [4] and [5], [4] does not involve HX formation at all and [5] suggests an important role for the direct interaction of the polymer substrate with the metal oxide prior to its reaction with the halogen compound. 

Antimony oxide is known as a flame retardant synergist when used in combination with halogen compounds. Volatile antimony oxyhalide (SbOX) and/or antimony trihalide (SbX3) are formed in the condensed phase and transport the halogen into the gas phase (3). It has been suggested that antimony is also a highly active radical trap (4). 

The SSP behavior of co-polyesters with rigid or voluminous comonomers, such as the flame retardant additive 9,10-dihydro[2,3-di-9-oxa-(2-hydroxyethoxy)-carbonylpropyl]-10-phosphaphenanthrene-10-oxide, or the ionic compound, sodium 5-sulfoisophthalate, is inhibited. This also occurs in the melt phase and cannot be improved by the use of catalysts [56], The results of studies examining the influence of employed catalysts with respect to stability and quality of the polymer suggest the use of antimony catalysts. The thermal or thermo-oxidative stability is, however, reduced by the interaction of the catalyst with the carboxylic groups of the polymer [57],... 

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