flame retardantIt exerts its flame retardant effect through several mechanisms, such as endothermic effect, covering effect, inhibition of chain reaction, asphyxiation of non-combustible gas, etc. Most flame retardants achieve the purpose of flame retardancy through the joint action of several mechanisms.

1. Endothermic effect

Any combustion in a short period of time the release of heat is limited, if you can in a short period of time to absorb part of the heat released by the fire, then the flame temperature will be reduced, radiation to the combustion surface and the role of the combustible molecules have been vaporized into free radicals of heat will be reduced, the combustion reaction will be a certain degree of inhibition. 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 flammable gases, and prevents the spread of combustion. The flame retardant mechanism of Al(OH)3 flame retardant is to increase the heat capacity of the polymer, so that it can absorb more heat before reaching the thermal decomposition temperature, thereby improving its flame retardant performance. This kind of flame retardant gives full play to its characteristics of a large number of heat absorption when combined with water vapor, and improves its own flame retardant ability.

2. The role of coverage

After the flame retardant is added to the combustible material, the flame retardant can form a glassy or stable foam coating at high temperature, isolate oxygen, have heat insulation, oxygen barrier, and prevent the escape of combustible gas, so as to achieve the purpose of flame retardant. Such as organic phosphorus flame retardant heat can produce a more stable structure of the cross-linked solid material or carbonized layer. On the one hand, the formation of the carbonized layer can prevent the further pyrolysis of the polymer, on the other hand, it can prevent the internal thermal decomposition organisms from entering the gas phase to participate in the combustion process.

Inhibition of chain reactions

According to the chain reaction theory of combustion, what is needed to sustain combustion is free radicals. 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 the end. Such as halogen-containing flame retardants, its evaporation temperature and polymer decomposition temperature is the same or similar, when the polymer is decomposed by heat, the flame retardant is also volatilized. 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, thereby preventing the propagation of the flame, reducing the flame density in the combustion zone, and finally reducing the combustion reaction speed until termination.

4. Asphyxiation effect of non-combustible gas

When the flame retardant is heated, the non-combustible gas is decomposed, and the concentration of the combustible gas decomposed by the 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, preventing the combustion from continuing and achieving the flame retardant effect.

5 Mechanism of combustion and flame retardant

In Section 3 and Tables 3 and 4, we discuss the basic thermal parameters that determine the inherent combustion behavior of textile fibers. In order to understand how existing textile flame retardants work and, more importantly, how to develop future flame retardants, the key is to explore the combustion mechanism of fiber-forming polymers in greater depth.