Flame-retardant textiles can be seen everywhere in our lives, and their applications cover many fields such as daily life, industry, agriculture, medical defense, aerospace, transportation, and military.
So, do you know how flame-retardant textiles achieve flame-retardant effects?
Flame retardant mechanism
Most of the textiles in our daily life are made of chemical fibers, cellulose fibers or a variety of fiber blends. Under the condition of a heat source, the heat can cause the fiber material to crack and produce combustible substances. These decomposition products will continue to oxidize and burn in the flame, and release a lot of heat, which will promote the continuous cracking of the fiber material and accelerate the combustion. The conditions for fabric burning are combustible materials, combustion-supporting materials and fire sources. Only by analyzing the conditions and processes of combustion can different flame retardant mechanisms be adopted according to the combustion process.
The flame-retardant finishing refers to the post-finishing of the fabric to reduce its flammability when exposed to an external heat source, delay the spread of combustion, and quickly extinguish the flame after removing the external heat source. For the combustion process of fabrics, flame retardancy is to cut off the circulation system of the interaction between the heat source, fabric and oxygen.
1. Mechanism of overburden flame retardant
Covering flame retardant is a chemical change of the flame retardant when it is heated and burned to produce a flame-retardant substance on the surface of the textile, forming an insulating covering layer.
This covering film can block the interaction between the fabric, oxygen and heat sources, and can hinder the diffusion of combustible gases, thereby playing a flame retardant effect. Both inorganic and organic flame retardants have the covering flame retardant mechanism, such as ammonium polyphosphate flame retardants are the covering flame retardant mechanism.
2. Gas phase flame retardant mechanism
There are two main theories for the gas phase flame retardant mechanism:
One is the gas dilution theory. Since the flame retardant is decomposed by heat to produce incombustible gas, which dilutes the concentration of the flammable gas, the oxygen is insufficient during the combustion of the fabric, so as to achieve the flame retardant effect.
The second is free radical theory. The pyrolysis products of flame retardants can interrupt the chain reaction of combustion, because the pyrolysis products can capture a large amount of high-energy oxygen free radicals and hydrogen free radicals during the combustion process, thereby exerting a flame retardant effect.
3. Decomposition endothermic flame retardant mechanism
The flame retardant undergoes endothermic decomposition reactions such as phase change, dehydration, etc. under heating. Because the flame retardant can absorb a certain amount of heat energy, it reduces the heating of the fabric, thereby reducing the thermal decomposition of the fabric and the generation of combustible gases.
4. Dehydration carbonization flame retardant mechanism
In the process of heating, the flame retardant promotes the dehydration, cyclization and cross-linking of the fiber by changing the thermal cracking of the fiber, thereby forming a carbon layer.
The formation of the carbon layer can reduce the generation of combustible gases, and can also cover and insulate the fabric. The flame retardants that act on this flame retardant mechanism are mostly phosphorus-containing flame retardants. It is generally believed that phosphate and organic phosphoric acid compounds have a flame retardant effect, because it has an esterification reaction with the hydroxyl group in the fiber macromolecule, which prevents the formation of L-glucose, and further dehydrates the cellulose to form unsaturated double bonds. It speeds up the cross-linking reaction between cellulose molecules, increases the carbon residue generation rate of the fabric, and achieves the purpose of flame retardancy.
In actual production and application, the structure of fabric and fiber type content are different, and the corresponding flame retardant types are also different. Therefore, the actual flame retardant effect and flame retardant mechanism are not determined solely. The flame retardant mechanism of the fuel may involve the combined effects of the above-mentioned flame retardant mechanisms. When flame retardants or flame retardant ingredients of different flame retardant mechanisms work together, they often produce better flame retardant effects due to their synergistic effects. There are two explanations for this synergistic effect. One is that the effect of multiple flame retardants or flame retardant ingredients is much stronger than when one is used alone; the other explanation is the addition of non-repellent to the flame retardant system. Combustible ingredients can increase flame retardancy. Such as the phosphorus-nitrogen synergistic effect. Among them, nitrogen-containing compounds such as urea and peptide amines do not have flame retardant ability. The flame retardant effect of phosphorus flame retardant is better.
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