Flame retardants stannates

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. 

Studies at the International Tin Research Institute showed that 2.5% zinc stannate strongly enhanced the flame retardant action of ATH in ethylene-acrylic rubber, and enhanced the char yield (34) (Fig. 5). 

Of the tin additives studied, the anhydrous and hydrated zinc stannates, ZnSnO and ZnSn(OH), respectively, are considerably more effective flame-retardant synergists with the bromine present in the plastic than 8-stannic acid (Figure 1). In line with this observation, oxidic tin-zinc systems have previously been found to exhibit superior flame-retardant properties to tin oxides alone (19-22). In addition, ZnSnO, gives higher values of 01 than Sb20, incorporation levels studied, and, in fact, the 1% ZnSnO - containing plastics outperform samples containing 2% Sb O,. 

Zinc hydroxystannate and zinc stannate are very effective flame-retardant synergists when incorporated at levels of 1-10% into... 

Cusack, P.A. and Hornsby, P.R., Zinc hydroxystannate/zinc stannate-coated fillers Novel flame retardants and smoke suppressants for polymeric materials, J. Vinyl Additive Technol., 5, 21-30, 1999. 

Metallic interlayer (MIL) influences the chemical processes of FR. The role of metal ions in the degradation process has been summarized by Lewin and Endo [30], The advantageous effect of a MIL around metal hydroxide flame retardants was utilized at first by Hornsby et al. [31]. They proposed a zinc-hydroxy-stannate (ZnHSt) layer, the detailed chemical-physical structure and 4.7 nm thickness... 

By far the most important tin-based fire retardants are the zinc stannates - zinc hydroxystannate (ZHS) and its anhydrous analog, zinc stannate (ZS). Originally developed at ITRI during the mid-1980s, these additives are now being marketed worldwide as non-toxic flame retardants and smoke suppressants for use in a wide range of polymeric materials. ... 

Zinc stannate is an inorganic flame retardant which can he used hy itself or in combination with aluminum hydroxide or magnesium hydroxide with which it forms synergistic mixtures of high performance flame retardants. It is frequently used as a surface coating on these two fillers. It reduces smoke emission and promotes char formation. 

Figure 13.7 shows the effect of two combinations on smoke release. Addition of zinc stannate or ammonium octamolybdate, AOM, gives better performance than antimony trioxide alone. " Antimony trioxide performance is also improved by brominated flame retardants. Chlorinated hydrocarbons, antimony trioxide, and novel silicone powders form good combinations, reducing the heat release rate and smoke in thermoplastics. ... 

There are several fillers and inoiganic/organic additives used in flame retarded materials and these include antimony oxide, aluminum trihydrate, zinc borate, ammonium octamolybdate, and zinc stannate. The details related to the composition required and performance characteristics of inorganic additives can be found in specialized monograph. Some of these compounds are discussed below in relation to their effects on enhancement of performance of phosphate plasticizers. 

Work in Poland has shown that zinc stannate and zinc hydroxystannate are the most efficient ignition and smoke retardants for GRP laminates, with antimony trioxide also being a good smoke suppressant. This appeared to be irrespective of the presence of other flame retardant additives. The resin systems also contained halogen additive or retardant components on the polyester backbone. 

Interest in tin compoimds as flame retardants for plastics has grown over the past 15 years. More than a dozen substances have been tried with some success, but only three of them, namely zinc hydroxystannate, zinc stannate and zinc oxide, are currently important. They all have low toxicity. Zinc stannate is preferred for use in polymers processed at temperatures over... 

Stannates. Zinc stannate [12036-37-2], Alcan s FLAMTARD S, and zinc hydroxystannate [12027-96-2], FLAMTARD HS, are both white water-insoluble powders useful as smoke suppressants in PVC. They can partly replace antimony oxide as flame-retardant synergists in halogen-containing flame-retardant formulations, with reduced smoke (16,17). 

Flame retardants inorganic oxide and hydroxide systems Zinc stannates... 

Tin oxide, Sn02, has also been studied as a flame retardant and smoke suppressant in conjunction with chlorine or bromine compounds. Performance was found to be generally less effective than that of the zinc stannates, which also contain less tin, and are hence more cost effective. 

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. 

More recently, tin salts have foimd use in flame-retardant treatments for woollen sheepskins and rugs. The active tin species are generally fluoro-stannate-based (e.g. SnF ), and these are electrostatically attracted to the protonated amino groups in the proteinaceous wool structure. 

Certain tin compounds, in particular, zinc hydroxystannate, zinc stannate and tin(iv) oxide, are effective flame retardants in a wide range of polymeric materials and offer several advantages over many of the available alternatives ... 

Keywords tin, tin oxide, zinc hydroxystannate, zinc stannate, organotin compounds, antimony trioxide, alumina trihydrate, magnesium hydroxide, titanium dioxide, molybdenum trioxide, iron oxide, zinc borate, alumina, halogenated flame retardants, metal halides, thermal analysis, Mossbauer spectroscopy, fire-retardant mechanism, ultrafine powders, coated fillers. 

The Charmax LS ZST is a zinc stannate of high purity and fine particle size and is used as a flame retardant and smoke suppressant in polymers. 

Thermal analysis experiments have clearly shown that tin-based fire retardants markedly alter both the initial pyrolysis and the oxidative burn off stages that occur during polymer breakdown These changes have been interpreted as being indicative of an extensive condensed phase action for the tin additive, in which the thermal breakdown of the polymer is altered to give increased formation of a thermally stable carbonaceous char at the expense of volatile, flammable products. The consequent reduction in the amount of fuel supplied to the flame largely accounts for the beneficial smoke-suppressant properties associated with zinc stannates and other tin-based fire retardants. 

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