Antimony/halogen systems

Either mechanism can be used to describe how antimony—halogen systems operate in both the condensed and vapor phases. In the condensed phase a chat that is formed during the reaction of the polymer, antimony trioxide, and the halogen reduces the rate of decomposition of the polymer therefore, less fuel is available for the flame (16). 

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

It is known that much of the antimony is vaporized during burning30 or char formation.28 The ignition behavior of polyester resins inhibited by antimony halogen systems has been considered to indicate the likelihood of gas-phase inhibition.23-24... 

Cotton, viscose, nylon, polypropylene, acrylic, polyester, or wool are generally used in carpets as the face or pile fabric over Neoprene latex. Carpets are usually flame retarded by back-coating with antimony-halogen system. The primary U.K. tests for carpet are BS 6307 198237 and BS 4790 1987,38... 

The synergistic action between antimony oxide and most types of halogenated FRs has been used with plastics for many years, and there are many highly efficient antimony/halogen systems in use. The combination is particularly effective, in controlled amounts, in plasticized PVC compounds. In other polymers that do not contain a halogen, a suitably chlorinated or brominated compound needs to be added to achieve the required properties. A special grade should be used if translucency is required. 

Traditional antimony/halogen systems are still in wide use because they are proven by years of successful applications in the electronic and electrical markets. There are many applications where thin sections (<1 mm) must be flame retarded to meet UL V-0 or V-5 standards where only halogen systems are effective. 

Zinc borates are predominately a condensed phase fire retardant. In a halogenated system such as flexible PVC, it is known to markedly increase the amount of char formed during polymer combustion whereas the addition of antimony trioxide, a vapor-phase flame retardant, has little effect on char formation. Analyses of the char show that about 80%-95% of the antimony is volatilized, whereas the majority of the boron and zinc from Firebrake ZB remains in the char (80% and 60%, respectively).48-56 The fact that the majority of the boron remains in the condensed phase is in agreement with the fact that boric oxide is a good afterglow suppressant. The mode of action can be summarized in the following equation (not balanced). 

Epoxy vinyl ester resins are a special class of unsaturated resin. This resin is made by capping an epoxy resin with methacrylic acid and then dissolving in styrene monomer to the desired viscosity. This gives mechanical properties similar to epoxy resins, but the processibility (low viscosity allowing for resin infusion processes) of an unsaturated polyester resin. As with unsaturated vinyl esters, the most common fire retardant vinyl ester resin is based on a resin made from a halogenated system, tetrabromobisphenol A. The level of bromine in the resin and the presence of antimony will determine the fire performance of the resin. These resins are normally used for corrosion resistant equipment or when fire performance and high mechanical properties are required. It is very difficult to get a low smoke value with a brominated vinyl ester resin again due to the fact that bromine... 

Tin compounds such as zinc stannate are the alternative that most closely approaches a direct replacement for antimony oxide in halogen systems. They do come at a cost premium, however. Like molybdenum compounds, tin based ones have the key advantage of effective smoke suppressancy. 

Joseph Storey has introduced a zinc hydroxystannate flame retardant, which it found to be the closest non-toxic alternative to antimony trioxide in halogenated systems. The new material also has excellent smoke suppression properties. In halogen-free systems, tin char formation occurs, leading to reductions in filler loadings and improved physical properties. 

There are expected to be V-0 non-halogenated systems containing NOR-1 for polypropylene mouldings in the future as the chemistries are explored and refined further. The lower levels of the additives and the absence of antimony trioxide provide better processibility, lower density, lower smoke emission and improved physical and mechanical properties. In addition, the new systems meet enviromnental goals and provide even safer use and recycling. 

Finally, nano-clay combinations with halogen/antimony oxide systems are showing some promise [49]. 

The synergist antimony oxide has been used in combination with halo-genated flame retardants for years to impart flame retardancy to plastics [1]. Today, many highly efficient antimony oxide/halogen systems are used to give flame retardancy properties to a wide variety of polymers. Complete or partial substitutes for antimony oxide in certain polymers have been reported [2] they are ferric oxide, zinc oxide, zinc borate and zinc stannate. Most of these synergists are effective with polyamides and epoxies when using a chlorinated flame retardant. 

Replaces antimony/halogen flame retardant system... 

Degradation products from both antimony-halogen based and nitrogen-phosphorus based flame retardants were studied using X-ray diffraction and atomic emission analysis. Evidence of the retardation mechanisms in use against combustion was obtained for each system and in each case emission of volatile combustion inhibitors at the degradation temperature of the polymer matrix was the critical factor. 11 refs BELARUS BELORUSSIA... 

Powdered antimony pentoxide is used primarily in plastics. Stabilizers used to prevent the particles from growing are caustic, and can react with the halogen in the formulation. This can result in color formation and a lower flame-retarding efficiency of the system. 

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). 

A significant advance in flame retardancy was the introduction of binary systems based on the use of halogenated organics and metal salts (6,7). In particular, a 1942 patent (7) described a finish for utilizing chlorinated paraffins and antimony(III) oxide [1309-64-4]. This type of finish was invaluable in World War II, and saw considerable use on outdoor cotton fabrics in both uniforms and tents. 

Catalytic Oxidation. Catalytic oxidation is used only for gaseous streams because combustion reactions take place on the surface of the catalyst which otherwise would be covered by soHd material. Common catalysts are palladium [7440-05-3] and platinum [7440-06-4]. Because of the catalytic boost, operating temperatures and residence times are much lower which reduce operating costs. Catalysts in any treatment system are susceptible to poisoning (masking of or interference with the active sites). Catalysts can be poisoned or deactivated by sulfur, bismuth [7440-69-9] phosphoms [7723-14-0] arsenic, antimony, mercury, lead, zinc, tin [7440-31-5] or halogens (notably chlorine) platinum catalysts can tolerate sulfur compounds, but can be poisoned by chlorine. 

The self-extinguishing characteristics of the chlorine-containing resins are improved by incorporation of antimony oxide but this approach is not possible where translucent sheet is required. As an alternative to chlorine-based systems a number of bromine-containing resins have been prepared and, whilst claimed to be more effective, are not currently widely used. It is probably true to say that fire-retarding additives are used more commonly than polymers containing halogen groupings. 

MRH Bromine 1.21/91, carbon tetrachloride 2.89/83, chlorine 3.85/82 Silane burns in contact with bromine, chlorine or covalent chlorides (carbonyl chloride, antimony pentachloride, tin(IV) chloride, etc.) [1], Extreme caution is necessary when handling silane in systems with halogenated compounds, as a trace of free halogen may cause violent explosions [2],... 

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