four principles of halogen-free flame retardants

Halogen free flame retardants have low smoke emission and no toxic or corrosive gases. Halogen free flame retardant additives are mainly phosphorus compounds and metal hydroxides. These two compounds do not volatilize and do not produce corrosive gases when burning. They are known as nuisance free flame retardants. The following is a brief introduction to the flame retardant principle of halogen free flame retardants.

1. endothermic action: any burning heat released in a shorter time is limited. If a portion of the heat released from the fire source is absorbed in a shorter time, the flame temperature will decrease, radiating to the burning surface and acting on the heat of cracking the combustible molecules that have been vaporized into free radicals, and the combustion reaction will be reduced. To a certain degree of inhibition. Under the high temperature conditions, the flame retardant has a strong endothermic reaction, absorbs some of the heat released from the combustion, reduces the temperature of the combustible surface, effectively inhibits the formation of combustible gas and prevents the spread of the combustion. The flame retardant mechanism of Al (OH) 3 flame retardant is to increase the heat capacity of the polymer, so that it absorbs more heat before it reaches the thermal decomposition temperature, thus improving its flame retardancy. These flame retardants give full play to their characteristics of absorbing large amounts of heat when combined with water vapor and improve their own flame retardancy.

2. coverage: after adding flame retardant in combustible materials, the flame retardant can form glass or stable foam cover layer at high temperature, isolate oxygen, heat insulation, prevent oxygen and prevent the flammable gas from escaping out, so as to achieve flame retardancy. If organic phosphorus resistance flame retardant is  heated, it can produce cross-linked solid material or carbonized layer with more stable structure. On the one hand, the formation of carbonized layer can prevent further pyrolysis of polymer, and on the other hand, it can prevent its internal thermal decomposition producing organisms into the gas phase and participate in the combustion process.

3. inhibition chain reaction: according to the chain reaction theory of combustion, free radicals are needed to maintain combustion. The flame retardants can act on the gas phase combustion zone, capture the free radicals in the combustion reaction, thus prevent the spread of the flame, reduce the flame density of the combustion zone, and eventually reduce the combustion reaction rate to the end. Such as halogen containing flame retardants, its evaporation temperature and polymer decomposition temperature are the same or similar, when the polymer is decomposed by heat, the flame retardant also evaporates at the same time. At the same time, the halogen flame retardant and the thermal decomposition product are in the gas phase combustion area. The halogen can capture the free radicals in the combustion reaction, thus prevent the flame propagation, reduce the flame density of the combustion zone, and eventually reduce the combustion reaction rate to terminate.

4. the asphyxiating effect of non combustible gas: when the flame retardant is decomposed into non combustible gas when heated, the concentration of combustible gas decomposed from combustible material is diluted below the lower limit of combustion. At the same time, it also has a dilution effect on the oxygen concentration in the combustion zone, which prevents the combustion from continuing and achieves the role of flame retardancy.

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