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Why is aluminum hydroxide used as a flame retardant?
 Time : 2020-05-30   Click :

Aluminum hydroxide as a flame retardant, because it can decompose the chemical binding water at high temperature (about 34.6%), this decomposition reaction is an endothermic reaction, so it can slow down the thermal degradation rate of the polymer, slow down or inhibit the combustion of the polymer, inhibit the temperature rise of the polymer, and promote carbonization and smoke suppression.In addition, the release of a large amount of water vapor can dilute the concentration of combustible, reduce the contribution of combustible gas to the combustion, resulting in reduced heat and smoke emissions from the system, which also helps to interrupt combustion.

When aluminum hydroxide is decomposed by heat, it releases water and absorbs a large amount of latent heat, which reduces the actual flame temperature on the surface of the material and slows down the rate of polymer degradation to low molecules, thus reducing the occurrence of combustibles.Water vapor uniform dilute the concentration of oxygen on the surface of the surface burning cannot take place, aluminum hydroxide to start decomposition temperature is about 205 ° C, 320 ° C has basically completed the dehydration reaction, release the water of crystallization, the absorption of latent heat, reduce the temperature (i.e., flame retardant technology of "cooling technology, produce the large amount of water vapor can dilute combustible gas.

In short, under the action of flame, the aluminum hydroxide filled into the polymer decomposes to absorb some of the heat released during combustion, which is equivalent to taking heat from the polymer, thereby reducing the temperature of the polymer and slowing down the degradation rate.This chemical cooling by dispersive heat absorption is the main reason for the flame retardancy of aluminum hydroxide.The water vapor released by the decomposition of aluminum hydroxide can dilute the concentration of the gas reactant in the flame area, and also has a cooling effect.The aluminum hydroxide is packed into the polymer to help form a carbonized layer when burned, which blocks both the entry of heat and oxygen and the escape of small molecules of flammable gases.Of course, the latter two flame retardants are much smaller than the first. Aluminum hydroxide is effective in slowing down the burning of the polymer, reducing the amount of smoke it produces, and in capturing harmful gases.In terms of use, aluminum hydroxide, unlike some organic additives, does not produce corrosive combustion products, nor does it evaporate and leak from the polymer.