The mechanism of magnesium hydroxide flame retardancy is mainly achieved through the synergy of the following several mechanisms:
Absorb heat and cool down
Magnesium hydroxide undergoes a decomposition reaction when heated to around 340℃, absorbing a large amount of heat and thereby reducing the surface temperature of the material. This process can delay the thermal degradation of polymer materials and inhibit the continuous progress of combustion reactions. Each gram of magnesium hydroxide absorbs approximately 1.36 kilojoules of heat when decomposing. This heat absorption effect can effectively slow down the heating rate of the material and gain valuable response time in the early stage of a fire.
Release non-flammable gas for dilution
During the decomposition process, a large amount of non-flammable gases such as water vapor will be released. These gases can dilute the concentration of oxygen and flammable gases in the surrounding environment of the material. When the oxygen concentration is lower than the critical value required for combustion, the spread of the flame will be effectively suppressed. Meanwhile, the presence of water vapor can also lower the temperature in the combustion area, creating a dual inhibitory effect.
Form an isolation layer
The magnesium oxide (MgO) produced by decomposition forms a dense solid protective layer on the material surface. This inorganic oxide layer has excellent thermal stability and barrier properties. It can not only prevent the transfer of oxygen and heat into the interior of the material, but also prevent the escape of flammable volatile substances, thereby physically blocking the continuous progress of the combustion chain reaction.
Catalytic carbonization
During the combustion process, the active oxides produced by the decomposition of magnesium hydroxide can promote the formation of a stable carbonized layer in the polymer matrix. This carbonized structure has higher thermal stability and barrier performance, and has a more lasting flame-retardant effect compared to simple melting and dripping. Meanwhile, the formation of the carbonized layer can also reduce the generation of toxic smoke and enhance fire safety.
Synergistic enhancement effect
When used in combination with other flame retardants (such as phosphorus-based flame retardants), magnesium hydroxide can form a synergistic flame retardant system through physical blending or chemical reactions. The mechanisms of action of different flame retardants complement each other. They can not only suppress the spread of flames through the gas phase but also prevent thermal decomposition through the condensed phase, thereby significantly enhancing the overall flame retardant efficiency.
