The flame retardant effect of metal hydroxide is mainly the release of water by heat absorption and decomposition, when it is added to the polymer with high filling amount, the flame retardant polymer is brought by metal hydroxide when it is decomposed by heat – a series of physical effects: the release of water and oxide by heat absorption and decomposition, offsetting the heat of the polymer, the evaporation of water and heat absorption, the formation of water vapor dilution of combustible gases, the high specific heat capacity of the filler and the carbonization effect, all of which will interrupt or delay the polymer combustion.
The flame-retardant mechanism of the two is similar.
The thermal decomposition process of magnesium hydroxide and aluminum hydroxide is the gaseous water generated by thermal decomposition can cover the flame, expel oxygen, dilute the combustible gas, and form an adiabatic layer on the surface of the plastic in contact with the flame to prevent the flow of combustible gas and prevent the spread of flame, which is similar to the charring effect of phosphorus flame retardants. The decomposition products of these two flame retardants are non-toxic substances, producing mineral phase, especially magnesium hydroxide, which has stronger neutralization ability with acid than aluminum hydroxide, and can neutralize the acidic and corrosive gases (SO2, NO2, CO2, etc.) produced during the burning of plastic more quickly.
Aluminum hydroxide (ATH)
Magnesium hydroxide (MH)
Thermal reaction process:
2AI(OH) 3→AI2O3 + 3H2O
The decomposition of 1g of aluminum hydroxide consumes 1.051J of heat.
Mg (OH)2→ MgO + H2O
Decomposition of 1g of magnesium hydroxide consumes 1.316J of heat.
The decomposition energy of Mg hydroxide (1.316kJ/g) is higher than that of aluminum hydroxide (1.051kJ/g), and the heat capacity is also 17% higher, which helps to improve the flame-retardant efficiency.
MH has lower smoke generation, and the smoke density of MH is lower than that of ATH (see Table 1. Comparison of smoke density of ATH and MH).
The smoke generation of the fuel barrier containing aluminum hydroxide is higher than that of the magnesium hydroxide mixture, and the smoke suppression is not as good as that of magnesium hydroxide. The charring effect of magnesium hydroxide is strong, and the charring amount is large, thus improving the flame-retardant efficiency and reducing the smoke production.
The thermal decomposition temperature of magnesium hydroxide is 330°C, the thermal decomposition temperature of aluminum hydroxide is 210°C, which is 100°C higher than aluminum hydroxide, so the plastic filled with magnesium hydroxide flame retardant can withstand higher processing temperature, because in the process of plastic processing to increase the processing temperature is conducive to speed up the extrusion speed, shorten the molding time
Magnesium hydroxide and aluminum hydroxide are two different flame retardants, in addition to the impact on the environment is about the same, these two flame retardants in the thermal reaction, decomposition temperature, flame retardant ability and other aspects have obvious contrast, magnesium hydroxide flame retardant performance are better than aluminum hydroxide flame retardant. Today to be from these aspects of each aspect of magnesium hydroxide and aluminum hydroxide two kinds of flame retardants comparison, I hope it can be helpful to you.