Most flame retardants achieve the purpose of flame retardation through the joint action of several mechanisms

2022-07-15 15:56:44

Flame retardants exert their flame retardancy through several mechanisms, such as endothermic effect, covering effect, inhibition of chain reaction, asphyxiation of non combustible gases, etc. Most flame retardants achieve the purpose of flame retardation through the joint action of several mechanisms.

1. Endothermic action

The heat released by any combustion in a short time is limited. If part of the heat released by the fire source can be absorbed in a short time, the flame temperature will be reduced, the heat radiated to the combustion surface and acting on the cracking of vaporized combustible molecules into free radicals will be reduced, and the combustion reaction will be inhibited to a certain extent. Under high temperature conditions, the flame retardant has a strong endothermic reaction, absorbs part of the heat released by combustion, reduces the temperature of the combustible surface, effectively inhibits the generation of combustible gases, and prevents the spread of combustion. The flame retardant mechanism of Al (OH) 3 flame retardant is to improve the flame retardant performance by increasing the heat capacity of the polymer to absorb more heat before reaching the thermal decomposition temperature. This kind of flame retardant gives full play to its large amount of heat absorption when combined with water vapor, and improves its own flame retardancy.

2. Coverage effect

After adding flame retardants to combustible materials, the flame retardants can form a glassy or stable foam covering layer at high temperature, isolate oxygen, and have the functions of heat insulation, oxygen isolation, and preventing combustible gases from escaping outward, so as to achieve the purpose of flame retardancy. For example, when heated, organic phosphorus resistant flame retardants can produce crosslinked solid substances or carbonated layers with more stable structures. On the one hand, the formation of carbonated layer can prevent the further pyrolysis of polymer, on the other hand, it can prevent the internal thermal decomposition products from entering the gas phase to participate in the combustion process.

3. Inhibitory chain reaction

According to the chain reaction theory of combustion, free radicals are needed to maintain combustion. The flame retardant can act on the gas-phase combustion zone to capture the free radicals in the combustion reaction, so as to prevent the spread of the flame, reduce the flame density in the combustion zone, and finally reduce the speed of the combustion reaction until it ends. For example, the evaporation temperature of halogen-containing flame retardants is the same or similar to the decomposition temperature of polymers. When the polymers are heated and decomposed, the flame retardants also volatilize at the same time. At this time, halogen-containing flame retardants and thermal decomposition products are in the gas-phase combustion zone at the same time, and halogen can capture free radicals in the combustion reaction, so as to prevent the spread of flame, reduce the flame density in the combustion zone, and finally reduce the combustion reaction speed until termination.

4. Asphyxiation effect of incombustible gas

When the flame retardant is heated, it decomposes incombustible gas, and dilutes the concentration of combustible gas decomposed by combustibles below the lower limit of combustion. At the same time, it can also dilute the oxygen concentration in the combustion zone, prevent the continuation of combustion, and achieve the effect of flame retardation.