Flame retardants are functional additives that endow flammable polymers with flame retardancy. They are mainly designed for the Flame Retardant of polymer materials. They exert their flame retardant effects through several mechanisms, such as heat absorption, coverage, inhibition of chain reactions, and incombustibility. Gas asphyxiation, etc. Most flame retardants work together to achieve the purpose of flame retardant through several mechanisms.
1. Endothermic effect
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 decrease, radiate to the combustion surface and act on the gas that has been vaporized. The heat required for the decomposition of 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 undergoes a strong endothermic reaction, absorbs part of the heat released by combustion, reduces the temperature of the surface of the combustible material, 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 its flame retardant performance by increasing the heat capacity of the polymer, so that it absorbs more heat before reaching the thermal decomposition temperature. This kind of flame retardant fully exerts its characteristic of absorbing a lot of heat when combined with water vapor, and improves its own flame retardant ability.
2. Coverage
After adding the flame retardant to the combustible material, the flame retardant can form a glass-like or stable foam cover at high temperature, isolate oxygen, and have the functions of heat insulation, oxygen isolation, and preventing the escape of combustible gas, so as to achieve flame retardant Purpose. For example, when the organic phosphorus flame retardant is heated, it can produce a cross-linked solid substance or a carbonized layer with a more stable structure. On the one hand, the formation of the carbonized layer can prevent the polymer from further pyrolysis, and on the other hand, it can prevent the internal thermal decomposition products from entering the gas phase to participate in the combustion process.
3. Inhibit the chain reaction
According to the chain reaction theory of combustion, it is free radicals that 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, thereby preventing the spread of the flame, reducing the flame density in the combustion zone, and finally reducing the combustion reaction speed until it is terminated. For example, halogen-containing flame retardants have the same or similar evaporation temperature as the polymer decomposition temperature. When the polymer is decomposed by heat, the flame retardant also volatilizes at the same time. At this time, the halogen-containing flame retardant and the thermal decomposition product are in the gas phase combustion zone at the same time, and the halogen can capture the free radicals in the combustion reaction and interfere with the chain reaction of the combustion.
4. Asphyxiating effect of non-combustible gas
When the flame retardant is heated, it decomposes into a non-combustible gas, and the concentration of the combustible gas decomposed from the combustible material is diluted to below the lower combustion limit. At the same time, it also has the effect of diluting the oxygen concentration in the combustion zone, preventing the continuation of the combustion and achieving the effect of flame retardant.
The vast majority of polymers are composed of hydrocarbons and other elements, which are highly flammable. The combustion process is a complex free radical chain reaction process, which will release a large amount of heat energy, causing direct damage and rapidly increasing the fire.
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