Alumina trihydrate ,

Mineral hydrates, such as alumina trihydrate and magnesium sulfate heptahydrate, are used in highly filled thermoset resins. 

Fillers that contain combined water or carbon dioxide, such as alumina trihydrate, Mg(OH)2, or dawsonite [12011 -76-6] increase fire resistance by hberating noncombustible gases when they are heated. These gases withdraw heat from the plastic and can also reduce the oxygen concentration of the air surrounding the composition. 

In 1990, appioximately 66,000 metric tons of alumina trihydiate [12252-70-9] AI2O2 3H20, the most widely used flame retardant, was used to inhibit the flammabihty of plastics processed at low temperatures. Alumina trihydrate is manufactured from either bauxite ore or recovered aluminum by either the Bayer or sinter processes (25). In the Bayer process, the bauxite ore is digested in a caustic solution, then filtered to remove siUcate, titanate, and iron impurities. The alumina trihydrate is recovered from the filtered solution by precipitation. In the sinter process the aluminum is leached from the ore using a solution of soda and lime from which pure alumina trihydrate is recovered (see Aluminum compounds). 

Alumina Trihydrate. Alumina trihydrate is usually used as a secondary flame retardant in flexible PVC because of the high concentration needed to be effective. As a general rule the oxygen index of flexible poly(vinyl chloride) increases 1% for every 10% of alumina trihydrate added. The effect of alumina trihydrate on a flexible poly(vinyl chloride) formulation containing antimony oxide is shown in Figure 5. 

Fig. 5. Effect of alumina trihydrate on the oxygen index of flexible PVC (30) having 5 phr Tribase XL, 3 phr Sb202, 0.05 phr petroleum wax, and (—...

TrialkylPhosphates. Triethyl phosphate [78-40-0] C H O P, is a colorless Hquid boiling at 209—218°C containing 17 wt % phosphoms. It may be manufactured from diethyl ether and phosphoms pentoxide via a metaphosphate intermediate (63,64). Triethyl phosphate has been used commercially as an additive for polyester laminates and in ceHulosics. In polyester resins, it functions as a viscosity depressant as weH as a flame retardant. The viscosity depressant effect of triethyl phosphate in polyester resins permits high loadings of alumina trihydrate, a fire-retardant smoke-suppressant filler (65,66). 

Most A1F. and cryoHte producers have their own HF production faciUties. HF vapor is reacted with alumina trihydrate to form A1F. in a fluid-bed reactor. HF is reacted with sodium hydroxide to form sodium fluoride, which is then used to produce cryoHte. Producers who manufacture these products solely for use in the aluminum industry do not generally install Hquid HF storage and handling faciHties, and do not participate in the merchant HF market. 

Typical gels are prepared from aqueous solutions of reactants such as sodium aluminate, NaOH, and sodium siUcate other reactants include alumina trihydrate (AI2O2 3H2O), coUoidal siUca, and siUcic acid. Some synthetic 2eohtes prepared from sodium aluminosihcate gels are given in Table 3. 

Flame retardants such as a-alumina trihydrate [14762-49-3] can be added to latex-based foamed carpet backing a combination of antimony oxide [1309-64-4] and chlorinated paraffins is used in dry mbber. 

Flame retardants (qv) are incorporated into the formulations in amounts necessary to satisfy existing requirements. Reactive-type diols, such as A/ A/-bis(2-hydroxyethyl)aminomethylphosphonate (Fyrol 6), are preferred, but nonreactive phosphates (Fyrol CEF, Fyrol PCF) are also used. Often, the necessary results are achieved using mineral fillers, such as alumina trihydrate or melamine. Melamine melts away from the flame and forms both a nonflammable gaseous environment and a molten barrier that helps to isolate the combustible polyurethane foam from the flame. Alumina trihydrate releases water of hydration to cool the flame, forming a noncombustible inorganic protective char at the flame front. Flame-resistant upholstery fabric or liners are also used (27). 

Some of the chemicals mentioned above and others, such as chlorinated mbber or paraffin, antimony trioxide, calcium carbonate, calcium borate, pentaerythrithol, alumina trihydrate, titanium dioxide, and urea—melamine—formaldehyde resin, may be used to formulate fire retardant coatings. Many of these coatings are formulated in such a way that the films intumesce (expand) when exposed to fire, thus insulating the wood surface from further thermal exposure. Fire retardant coatings are mostly used for existing constmction. 

An abrasive is usually chemically inert, neither interacting with other dentifrice ingredients nor dissolving in the paste or the mouth. Substances used as dentifrice abrasives include amorphous hydrated silica, dicalcium phosphate dihydrate [7789-77-7] anhydrous dicalcium phosphate [7757-93-9] insoluble sodium metaphosphate [10361-03-2], calcium pyrophosphate [35405-51-7], a-alumina trihydrate, and calcium carbonate [471-34-1]. These materials are usually synthesized to specifications for purity, particle size, and other characteristics naturally occurring minerals are used infrequently. Sodium bicarbonate [144-55-8] and sodium chloride [7647-14-5] have also been employed as dentifrice abrasives. 

Alumina trihydrate - to achieve reduclion of heal by cooling through an endothermic process that decomposes Ihe flame... 

Some inorganic fillers are used as flame retardants in rubber base formulations. Flame retardants act in two ways (1) limiting or reducing access of oxygen to the combustion zone (2) reacting with free radicals (especially HO ), thus acting as terminator for combustion-propagation reaction. The additives most widely used as flame retardants for polymers are antimony oxides and alumina trihydrate. 

Fillers. Addition of fillers is not common in polychloroprene latex formulations. Fillers are used to reduce cost and control rheology, solids content and modulus. However, cohesion and adhesion are reduced. Calcium carbonate, clay and silica are some of the fillers than can be added. Alumina trihydrate is often used when resistance to degradation by flame is important. 

After formulation with a flame retardant filler such as alumina trihydrate Al203 3H20, hydrated silica or calcium carbonate, a peroxide curing agent and... 

As an example, a foam prepared from III, alumina trihydrate as a filler, benzoyl peroxide as a curing agent, and azobis formamide as a blowing agent, leads to a material with an oxygen index of 48, a long-term stability to at least 150 °C, and a smoke density about one fifth that of a commercial foam [284]. 

In other halogen-containing systems, such as flexible PVC and polyolefins, it is preferable to use the zinc borate in conjunction with antimony oxide for maximum performance. In flexible PVC, for example, the zinc borate alone is not very effective in the Oxygen Index test (Fig. 6), but a combination of the zinc borate and antimony oxide (1 1 ratio) outperforms equal weight of antimony oxide at a total loading of more than 10 phr (4). In the presence of alumina trihydrate (ATH), the beneficial effect of using a combination of the zinc borate and antimony oxide is dramatically increased (Fig. 7). 

Fig. 7. Oxygen Index of Flexible PVC Formulations Containing Alumina Trihydrate (30 phr). ZB - Zinc Borate. (Reproduced with permission from Ref. 2. Copyright Plastics Compounding 1985).

Fig. 10. NBS Smoke Test of Flexible PVC Containing Alumina Trihydrate. ZB - Zinc Borate.

Fig. 11. NBS Smoke Test of Ethylene-Vinyl Acetate. ZB -Zinc Borate, ATH - Alumina Trihydrate.

Fig. 12. Scanning electron micrographs (6000 x) of residues of air-pyrolyses of halogen-free ethylene-vinyl acetate, containing Zinc Borate (33%) and alumina trihydrate (ATH) (33%). At 500°C (top picture), a powdery residue was obtained no sintering took place between the Zinc Borate (small particles) and ATH (large particles). At 550°C (bottom picture), a hard and porous residue was obtained Zinc Borate acted as a sintering agent. A hard and porous residue is a good thermal barrier.

As a result, several inorganic compounds have found application in this field, and alumina trihydrate, A1(0H)-, is now by far the highest volume flame retardant (3). Its use, however, is limited to those polymers which can tolerate the exceptionally high loadings required to be effective, without seriously affecting the mechanical properties of the substrate (7 ). 

It is of interest to note that the polymer containing ZnSn(OH) does not burn in air even at 250°C and, accordingly, this composition has a temperature index of at least 50°C above that of the rubber containing ATH alone. The 01 and high temperature 01 data therefore provide substantial evidence as to the benefit of using ZnSn(OH) as a flame-retardant synergist with alumina trihydrate filler. 

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