Trihydrated aluminum hydroxide (ATH) is an acidic, halogen-free flame retardant widely employed in various plastics. Both compounds can undergo decomposition under endothermic conditions according to the following reaction: 2Al(OH)3⟶Al2O3+3H2O2Al(OH)3⟶Al2O3+3H2O. Gaseous water vapor is believed to cover the flame, excluding oxygen and diluting combustible gases. Similar to the function of phosphorus-containing flame retardants that form char, ATH, when in contact with the flame, creates a thermal-insulating substance on the material surface, reducing the likelihood of combustion decomposition products flowing into the combustible gas phase. In the above reaction, the decomposition product is a non-toxic mineral phase.
Aluminum hydroxide exhibits high chemical stability at room temperature but begins to undergo endothermic decomposition, releasing three crystal waters, when heated to around 220 degrees. The decomposition equation is 2Al(OH)3→heatAl2O3+3H2O2Al(OH)3heatAl2O3+3H2O. This endothermic dehydration process retards the combustion of polymers. Aluminum hydroxide acts as a heat sink, slowing down the combustion rate. Simultaneously, the released water vapor not only dilutes the combustion gases but also participates in reactions in the condensed phase. The heat-absorbing decomposition is based on the fact that aluminum hydroxide absorbs a significant amount of heat during decomposition and only releases steam during heated decomposition, avoiding the production of toxic, flammable, or corrosive gases.
Therefore, aluminum hydroxide, as a flame-retardant filler, possesses a triple function: filling, flame retardancy, and smoke suppression. It has garnered special attention in the material industry for providing effective flame retardant performance without generating harmful gases, making it widely used in plastic products.
