The flame retardant mechanism of aluminium hydroxide flame retardant is mainly achieved through the synergistic effect of the following several mechanisms:
Heat absorption and cooling: When aluminum hydroxide is heated to around 200℃, it begins to decompose, absorbing a large amount of heat, lowering the surface temperature of the material, and delaying combustion. Each gram of aluminium hydroxide absorbs up to 878 joules of heat. The decomposition process is equivalent to a heat sink, slowing down the combustion rate. Partial water loss begins at around 230℃, further at around 300℃, and is completely transformed into alumina at around 500℃. All these stages are accompanied by heat absorption peaks.
Diluting flammable gases: The water vapor and non-flammable gases produced by decomposition dilute the concentration of flammable gases and oxygen, weakening the combustion reaction. Meanwhile, water vapor participates in the condensation reaction, further suppressing combustion.
Covering isolation: The aluminum oxide generated by decomposition forms a dense protective film on the surface of the combustible material, isolating the contact between oxygen and the combustible material and preventing the combustible material from continuing to burn. Alumina can also adsorb smoke and dust particles, playing a role in suppressing smoke.
Promoting carbonization: Under combustion conditions, aluminium hydroxide generates a strong dehydrating substance, forming a carbonized layer on the surface of materials such as plastics. This carbonized layer can not only prevent heat and oxygen from entering, but also prevent the escape of small-molecule flammable gases, thereby preventing the spread of flames.
Physical dilution effect: As a filler, aluminium hydroxide reduces the proportion of flammable substances in the polymer matrix, lowering the risk of combustion through physical means.
