In the 1950s, with the explosive development of materials technology, organic polymer materials began to be widely used in various fields of production and life. Plastics, rubber, textiles, and coatings with polymer materials as the main components have become our indispensable production elements. Electrical appliances, tableware, vehicles and other items made of polymer materials have brought great convenience to our lives while also bringing There are a lot of security risks.
Due to the low oxygen index of polymer materials, air with an oxygen content of 21% is sufficient to meet the combustion conditions of most polymer materials. In addition, when polymer materials burn, they release smoke and toxic gases, which not only endanger human health, but also cause environmental pollution. In order to reduce the flammability of polymer materials and prevent fires, flame retardants have emerged. Flame retardants, as the name suggests, are additives that can be used to prevent the flammability of materials, that is, prevent materials from being ignited and inhibit flame propagation.
There are many types of flame retardants, which can be roughly divided into organic flame retardants and inorganic flame retardants. Among them, organic flame retardants include halogen flame retardants, phosphorus-nitrogen flame retardants, organic phosphorus flame retardants, silicone flame retardants and the like. We select several types of Flame Retardant mechanisms to introduce.
Halogen flame retardant is an important member of organic flame retardants, and its main component is halogen organics. The free radicals produced by polymer degradation under high temperature conditions are the factors that maintain the combustion of organic matter, and the hydrogen halide (HX) gas produced by halogen flame retardants when heated to decompose can capture free radicals, so as to achieve the purpose of preventing flame diffusion. In addition, hydrogen halide itself cannot burn and is denser than air. It forms a gas barrier on the surface of the polymer material to prevent the polymer material from contacting oxygen.
Phosphorus-nitrogen flame retardants use phosphorus and nitrogen as main elements. This type of flame retardant is also called Intumescent Flame Retardant, because when it is heated, a uniform carbon foam layer can be produced on the surface of this type of flame retardant, which can isolate heat and oxygen. The intumescent flame retardant system generally consists of three parts: acid source (dehydrating agent), carbon source (charging agent) and gas source (nitrogen source, foaming source). After being heated, the acid source releases the esterified polyol and the inorganic acid that can be used as the dehydrating agent; the temperature further increases, the inorganic acid and the polyol (carbon source) react to form esters, and they are in a viscous molten state.
The water vapor generated during the reaction and the incombustible gas generated by the gas source expand and foam the molten system. At the same time, the polyols and esters are dehydrated and carbonized to form inorganic substances and carbon residues. As the temperature rises With the progress of the reaction, the system gels and solidifies, and finally a porous carbon foam layer is formed.
Inorganic flame retardants mainly include expandable graphite, hydroxide, red phosphorus or polyphosphate, etc. Generally, several different inorganic substances are mixed and used. Under high temperature, expanded graphite expands rapidly, and the surface of the polymer forms a tough carbon layer, which can separate combustibles from the heat source; when the hydroxide is heated, it absorbs a large amount of heat and releases water vapor, dilutes the combustible gas, and generates refractory metal oxidation.
Red phosphorus or polyphosphate burns to produce polymetaphosphoric acid glass body, which can cover the surface of the combustion body to form a protective film. At the same time, the phosphoric acid formed has strong dehydration properties and can carbonize the polymer to form a carbon isolation layer.
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