Flame retardant material
Flame retardant material
Flame retardants, also known as flame retardants, fire retardants or fire retardants, are functional additives that endow flammable polymers with flame retardancy; Most of them are compounds of group V A (phosphorus), VII a (bromine, chlorine) and III A (antimony, aluminum) elements in the periodic table of elements.
Molybdenum compounds, tin compounds and iron compounds with smoke suppression also belong to the category of flame retardants. They are mainly applicable to plastics with flame retardant needs. They delay or prevent the combustion of plastics, especially polymer plastics, so that their ignition time increases, ignition self extinguishing and difficult to ignite.
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Flame retardant principle
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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 gasified combustible molecules into free radicals will be reduced, and the combustion reaction will be restrained 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 surface temperature of combustibles, 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 to improve its flame retardant ability.
2) Covering effect
After adding flame retardants in combustible materials, flame retardant can form glass or stable foam covering at high temperature, and isolate oxygen, which has the function of heat insulation, oxygen isolation and preventing flammable gas from escaping outward, so as to achieve the purpose of flame retardancy.
For example, when organic phosphorus retardant is heated, it can produce crosslinked solid substances or carbonized layers with more stable structure.
On the one hand, the formation of carbonization layer can prevent the further pyrolysis of polymer, on the other hand, it can prevent the internal thermal decomposition organisms 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. Flame retardant can act on the gas phase combustion zone to capture the free radicals in the combustion reaction, so as to prevent the propagation of flame, reduce the flame density in the combustion zone, and finally reduce the combustion reaction speed until it is terminated.
For example, the evaporation temperature of halogen-containing flame retardant is the same or similar to the decomposition temperature of polymer. When the polymer is decomposed by heating, the flame retardant also volatilizes 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, halogen can capture free radicals in the combustion reaction, so as to prevent the propagation of flame, reduce the flame density in the combustion zone, and finally reduce the combustion reaction speed until it is terminated.
4) Asphyxiation of incombustible gas
When the flame retardant is heated, it decomposes non combustible 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.
