Flame Retardant Mechanism

Polymer materials are easily decomposed to generate flammable gases when heated. When they reach a certain level, the polymer materials will burn. Therefore, the combustion process of high-grade materials can be roughly divided into two stages, one is the stage of thermal decomposition of polymer materials to generate flammable gas, and the other is the normal combustion stage of polymer materials. These two stages are related to heat. Inorganic flame retardant materials for transmission, degradation of high-grade materials, diffusion and mixing of flammable gases, and combustion in the gas phase.

At present, a large amount of additive halogen flame retardants (halogen-antimony system) are used. The main flame retardant is the hydrogen halide and antimony halide released by them. They mainly capture the highly active Free radicals to stop burning. However, its flame retardant efficiency is low, and a large amount of flame retardants need to be added to meet the demand. At present, some high-efficiency combustion inhibitors have been developed. For example, a small amount of certain catalysts (such as Mn, Sn, and U salts) can be combined with free radicals in the gas phase, thereby eliminating a large number of free radicals in the gas phase and preventing combustion. Efficiency is one to two orders of magnitude higher than antimony trichloride. Adding a free radical inhibitor (a type of antioxidant) to polymer materials can delay the oxidation of the surface of the material and reduce the oxidative degradation rate of the polymer material. Therefore, in principle, it has a flame retardant effect and is conducive to extinguishing the combustion. 

Catalytic flame retardant systems refer to those systems that can dehydrate to acid and promote the formation of carbon from polymer materials under certain conditions. Phosphorus-containing flame retardants and intumescent flame retardants that are widely used today are such flame retardant methods. During the combustion process of polymer materials, a large amount of smoke and gas will be generated. Among them, the gas is mainly flammable gas and toxic gas, which is the factor that causes the highest mortality in fires. The generated gas and smoke have a faster propagation and diffusion speed than the flame, and most gases such as CO, HCl and HCN will have a certain toxic effect on the human body, and the generated smoke will obstruct people's vision and affect the evacuation of people. Therefore, when preparing flame-retardant polymer materials, researchers usually take certain measures to reduce the gases and fumes generated during combustion.

However, the amount of smoke generated during the thermal cracking or combustion of polymer materials is not an inherent property of the material, but is closely related to the combustion conditions and environmental conditions. However, the molecular structure of polymer materials is undoubtedly one of the important factors affecting the amount of smoke generated . High-molecular materials with a polyolefin structure and a benzene ring in the side chain usually have low smoke generation, because the polyene carbon chain can be graphitized carbon particles through cyclization and polycondensation during combustion or fully burned, and the smoke generation is low; With a benzene ring on the side chain, it is easy to generate unsaturated hydrocarbons with conjugated double bonds, which can continue to cyclize and polycondensate to carbon.

In general, if the polymer has high thermal stability and carbon formation rate, A dense carbon layer is formed on the surface during combustion to hinder the diffusion of volatile products, which can effectively reduce the amount of smoke generated.