Flame retardants, aluminum trihydrate

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). 

Nano-modified aluminum trihydrate show a good synergistic characteristics for improving the flame retardant properties of HIPS, when combined with red phosphorus (23). 

Additive flame-retardants may be more easily incorporated in polyurethane formulation. Several class of compounds have been used to improve flame retardancy of PU foams such compounds are halogen- (very often chloroalkyl-phosphate) or phosphorous-based compounds, although also other substances, like as EG, melamine, aluminum trihydrate and magnesium hydroxide, may be used. 

Journal of Applied Polymer Science 89, No.3, 18th July 2003, p.753-62 MECHANOCHEMICAL IMPROVEMENT OF THE FLAME-RETARDANT AND MECHANICAL PROPERTIES OF ZINC BORATE AND ZINC BORATE-ALUMINUM TRIHYDRATE-FILLED POLY (VINYL CHLORIDE)... 

Aluminum Trihydrate. The utility of aluminum trihydrate as a flame retardant is based on its endothermic dehydration to aluminum oxide and water. In absorbing some of the heat of combustion and lowering the temperature of the substrate near the flame, the hydrate functions as a chemical heat sink. The water vapor provided by such action dilutes the gaseous reactants in the flame until all the water of crystallization is exhausted. 

Common flame retardants are aluminum trihydrate, brominated compounds, phosphorous compounds, antimony oxide, chlorinated compounds, and boron compounds. Brominated flame retardants are preferred for thermoplastic resins such as polystyrene, polyesters, polyolefins and polyamides but are also used in epoxies, ABS and polycarbonates. Decabromodiphenyl oxide is the most common brominated flame retardant used. 

Beyer, G. Flame retardant properties of EVA-nanocomposites and improvements by combination of nanofillers with aluminum trihydrate. Fire Mater. 2001, 25, 193-197. 

In both Europe and the United States, aluminum trihydrate, or ATH [Al(OH)3)], has by far the largest share of the mineral flame-retardant market however, magnesium hydroxide presently has the highest growth rate. To date, most of the research using magnesium hydroxide has focused on thermoplastics, including ethylene-vinyl acetate copolymer (EVA), polypropylene, acrylonitrile-butadiene-styrene (ABS) copolymer, and modified polyphenylene oxide (Hornsby and Watson, 1986). 

Asbestos, either powdered or in fiber form, imparts heat resistance aluminum trihydrate and talcum act as flame retarders mica gives excellent electrical properties and aluminum powder improves heat transfer. Powdered minerals such as silica or china clay are often used to Improve water resistance. One novel area is the use of hollow glass spheres in rigid polyurethane foam, known as "diafoam," to achieve 30-70% higher flexural and compression moduli. This foam is used as "structural foam" in furniture. 

Miscellaneous. These approaches include dilution of the polymer with nonflammable materials (for example, inorganic fillers), incorporation of materials that decompose to nonflammable gases such as carbon dioxide, and formulation of products that decompose endothermically. A typical example of such a flame retardant is aluminum oxide trihydrate (AI2O3.3H2O). This type of material acts as a thermal sink to increase the neat capacity of the combusting system, lower the polymer surface temperature via endothermic events, and dilute the oxygen supply to the flame, thereby reducing the fuel concentration needed to sustain the flame. 

HDPE filled with a flame-retardant ATH (aluminum trihydrate) showed the ignition temperature of 445°C (833°F). The 10°C delay was caused by ATH, which releases water vapor at about 180-240°C (360-460°E), which that in turn cools down the material. 

A typical example of active flame retardants is represented by ATH, that is, aluminum trihydrate. When ATH is heated with a heating rate of 10°C/min, it starts releasing water at about 225°C (437°F). At 300°C, ATH releases 12% water by weight. At 334°C (633°F), the rate of water reaches its maximum, with about 28% of water release, and the process slows down, reaching 35% of water release at 900°C. Water release reduces the heat from the oxidized plastic and quenches flames. 

Aluminum trihydrate, magnesium hydroxide, calcium and zinc molybdates, antimony pentoxide, and zinc borate are examples of inorganic compounds used as flame retardants in the manufacture of household furniture, upholstery, wall coverings, draperies, and carpets (National Research Council (NRC), 2000). Antimony trioxide is sometimes used in combination... 

In 2007, over a million metric tons of flame retardants were sold on the world market, 40 % of which was for aluminum trihydrate (ATH). 

Chem. Descrip. Aluminum trihydrate CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Flame retardant, filler for polyester, acrylic, and epoxy resins, polyurethanes (casting resins), powd. coatings Propertes Povird. = 4 pm median particle size bulk dens. = 530 kg/m oil absorp. = 21 cmVIOO g conduct. <140 p cm < 0.35% moisture Martinal ON-906 (Martinswerk GmbH Lonza]... 

Chem. Descrip. Aluminum trihydrate CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Flame retardant, filler for polyester (laminates, artificial marble), epo) resins, paints, varnishes... 

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. 

Synergistic flame retardancy Nanocomposites have been demonstrated to reduce flammability, particularly through lowering peak heat release in cone calorimeter experiments. In combination with conventional flame retardants such as magnesium hydroxide or aluminum trihydrate, several polyolefin-based wire and cable products have been developed that incorporate 5% nanoday to reduce the use of conventional fire retardant agents and to improve physical properties [14, 15]. 

Metal hydroxides, particularly aluminum trihydrate and magnesium hydroxide, contribute to several fire-retardant actions. They first decompose endothermically and release water. The endothermic decomposition serves to remove heat from the surroundings of the flame and, thus, cool the flame. This is often referred to as the heat sink phenomenon. Pyrolysis decreases in the condensed phase as a result of... 

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