Flame retardant textiles can be seen everywhere in our life, and its application range covers daily life, industry, agriculture, medical defense, aerospace, transportation, military and many other fields.
    So, do you know how flame retardant textiles achieve flame retardant effect?
    Ammonium polyphosphate flame retardant
    Flame retardant mechanism most of the textiles in our daily life are made of chemical fiber, cellulose fiber or a variety of fibers. Under the condition of heat source, the heat can make the fiber materials split 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 fiber materials and accelerate the combustion. The conditions of fabric burning are: combustibles, combustion supporting materials and fire sources. Only by analyzing the combustion conditions and process, can we adopt different flame retardant mechanism according to the combustion process.
    The flame retardant finishing is to reduce the flammability of the fabric under the action of external heat source, delay the combustion spread speed, and quickly extinguish the flame after removing the external heat source. For the fabric combustion process, flame retardant is to cut off the circulation system of the interaction among heat source, fabric and oxygen.
    1. Flame retardant mechanism of coating
    Covering flame retardant is a kind of insulating covering layer formed by the chemical change of flame retardant on the surface of textiles when it is heated and burned.
    This film can block the interaction between the fabric and oxygen, heat source, and can hinder the diffusion of combustible gases, thus playing a role of flame retardant. Both inorganic and organic flame retardants have covered flame retardant mechanism, such as ammonium polyphosphate.
    2. Gas phase flame retardant mechanism
    There are two main theories of gas phase flame retardant mechanism
    One is the theory of gas dilution. Due to the non combustible gas produced by the thermal decomposition of flame retardant, the concentration of combustible gas is diluted, so the oxygen is insufficient in the process of fabric combustion, so as to achieve the effect of flame retardant.
    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 number of high-energy oxygen free radicals and hydrogen free radicals in the combustion process, so as to play the role of flame retardant.
    3. Decomposition, endothermic and flame retardant mechanism
    The flame retardant undergoes endothermic decomposition reaction, such as phase transformation, dehydration and so on. Because the flame retardant can absorb certain heat energy and reduce the heating of the fabric, the thermal decomposition of the fabric and the generation of combustible gas are reduced.
    4. Mechanism of dehydration and carbonization
    During the heating process, the flame retardant can promote the dehydration, cyclization and cross-linking of the fiber by changing the pyrolysis of the fiber, and then form a carbon layer.
    The formation of carbon layer can reduce the generation of combustible gas, and can also cover and isolate the fabric. The flame retardants based on this mechanism are mostly phosphorus containing flame retardants. It is generally believed that phosphates and organophosphates have flame retardancy because they react with hydroxyl groups in fiber macromolecules to prevent the formation of L-glucose, further dehydrate cellulose, form unsaturated double bonds, accelerate the cross-linking reaction between cellulose molecules, improve the carbon residue formation rate of fabric, and achieve the purpose of flame retardancy.
    In the actual production and application, the fabric structure and fiber type content are different, and the corresponding flame retardant types are not the same. Therefore, the actual flame retardant effect and flame retardant mechanism are not single determined. The flame retardant mechanism of a flame retardant may involve the comprehensive effect of the above flame retardant mechanisms.
    When the flame retardants or flame retardant components with different flame retardant mechanisms work together, they often produce better flame retardant effect because of their synergistic effect. There are two explanations for the synergistic effect. One is that the effect of multiple flame retardants or flame retardants is much stronger than that of single flame retardant;
    Another explanation is that adding non flame retardant components to the flame retardant system can increase the flame retardancy. For example, the synergistic effect of phosphorus and nitrogen, nitrogen-containing compounds such as urea, peptide amine and so on, have no flame retardancy. However, when they are used to finish fabrics with phosphorus containing flame retardants, it is found that their flame retardancy is better than that of only phosphorus containing flame retardants.