Flame retardants are invisible patron saints
Flame retardants (fire retardants; flame retardants), also known as flame retardants, fire retardants or fire retardants: functional additives that impart flame retardant properties to flammable polymers; they are divided into additive flame retardants and reactive flame retardants according to application methods. fuel.
The additive flame retardant is directly mixed with resin or rubber compound, which is easy to process, has a wide range of adaptability, and is the main body of the flame retardant.Reactive flame retardants are often bonded to the polymer chain as monomers, which have little impact on product performance and long-lasting flame retardant effects.
According to the composition, additive flame retardants mainly include inorganic flame retardants, halogen flame retardants (organic chlorides and organic bromides), phosphorus flame retardants (red phosphorus, phosphoric acid esters and halogenated phosphoric acid esters, etc.) and nitrogen Department of flame retardants, etc. In addition, molybdenum compounds, tin compounds and iron compounds with smoke suppression effect also belong to the category of flame retardants.
Flame Retardant - Flame Retardant Mechanism
The flame retardant exerts its flame retardant effect through several mechanisms, such as endothermic effect, covering effect, inhibition of chain reaction, suffocation effect of non-combustible gas, etc. Most flame retardants work together to achieve the purpose of flame retardant through several mechanisms.
endothermic effect
The heat released by any combustion in a short time is limited. If part of the heat released by the fire source can be absorbed in a short time, the flame temperature will be reduced, radiating to the combustion surface and acting on the gas that has been vaporized.The heat required for the decomposition of combustible molecules into free radicals will be reduced, and the combustion reaction will be inhibited to a certain extent. Under high temperature conditions, the flame retardant undergoes a strong endothermic reaction, absorbs part of the heat released by combustion, reduces the temperature of the surface of the combustible material, effectively inhibits the generation of combustible gas, and prevents the spread of combustion. The flame retardant mechanism of Al(OH)3 flame retardant is to improve its flame retardant performance by increasing the heat capacity of the polymer, so that it absorbs more heat before reaching the thermal decomposition temperature. This kind of flame retardant fully exerts its characteristic of absorbing a lot of heat when combined with water vapor, and improves its own flame retardant ability.
covering effect
After adding the flame retardant to the combustible material, the flame retardant can form a glass-like or stable foam cover at high temperature, isolate oxygen, and have the functions of heat insulation, oxygen isolation, and preventing the escape of combustible gas, so as to achieve flame retardant Purpose. For example, when the organic phosphorus-inhibiting flame retardant is heated, it can produce a cross-linked solid substance or a carbonized layer with a more stable structure. On the one hand, the formation of the carbonized layer can prevent the polymer from further pyrolysis, and on the other hand, it can prevent the internal thermal decomposition products from entering the gas phase to participate in the combustion process.
Inhibit chain reaction
According to the chain reaction theory of combustion, free radicals are needed to maintain combustion. 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 termination. For example, halogen-containing flame retardants have the same or similar evaporation temperature as the polymer decomposition temperature. When the polymer is decomposed by heat, the flame retardant also volatilizes at the same time. 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 spread of the flame, reducing the flame density in the combustion zone, and finally reducing the combustion reaction speed until termination. .
suffocating effect of non-combustible gas
When the flame retardant is heated, it decomposes into a non-combustible gas, and the concentration of the combustible gas decomposed from the combustible material is diluted to below the lower limit of combustion. At the same time, it also has the effect of diluting the oxygen concentration in the combustion zone, preventing the continuation of the combustion and achieving the effect of flame retardant.
Flame Retardants - Main Types
According to different classification standards, flame retardants can be divided into the following categories:
According to the content of flame retardant elements
According to the flame retardant elements contained, flame retardants can be divided into halogen flame retardants, phosphorus flame retardants, nitrogen flame retardants, phosphorus-halogen flame retardants, phosphorus-nitrogen flame retardants, etc.
According to the different components
According to the different components, it can be divided into three types: inorganic salt flame retardants, organic flame retardants and organic and inorganic mixed flame retardants.
Inorganic flame retardants are the most widely used type of flame retardants. Its main components are inorganic substances. The main application products are aluminum hydroxide, magnesium hydroxide, monoammonium phosphate, diammonium phosphate, ammonium chloride, boric acid, etc.
The main components of organic flame retardants are organic substances, and the main products are halogenated, phosphoric acid esters, halogenated phosphoric acid esters, etc.There are also some organic flame retardants used for the durable flame retardant of textile fabrics, such as hexabromo water dispersion and antimony decabromide trioxide flame retardant system, which have good flame retardant properties of washing resistance.
Organic and inorganic mixed flame retardants are improved products of inorganic salt flame retardants, mainly using water-insoluble organic phosphate water emulsion to partially replace inorganic salt flame retardants. Among the three major types of flame retardants, inorganic flame retardants have the advantages of non-toxic, harmless, smoke-free and halogen-free, and are widely used in various fields. The total demand accounts for more than half of the total demand for flame retardants, and the demand is growing. rate has an increasing trend.
According to the method of use
According to the different methods of use, flame retardants can be divided into additive type and reactive type. Additive flame retardants mainly play the role of flame retardants by adding flame retardants to combustibles. Reactive flame retardants introduce flame retardant groups into polymer materials through chemical reactions, thereby improving the flame resistance of materials, preventing materials from being ignited and inhibiting the spread of flames. Among the types of flame retardants, additive flame retardants dominate and are used in a wide range, accounting for about 85% of flame retardants, and reactive flame retardants only account for 15%.
