1. Flame retardant
Flame retardants are additives used in fire retardant combustible materials that render combustible materials flame-retardant. Flame retardants can be divided into reactive flame retardants and additive flame retardants. In field of plastics processing, additive flame retardants are mainly used, and the matrix resin is combined with flame retardant components by mixing and coating together to form a flame retardant. material.
2. Fire retardant classification
The types of flame retardants currently used to make flame retardant plastics mainly include brominated flame retardants, phosphorus-based flame retardants, ammonium salt inorganic flame retardants, metal compound-based flame retardants, etc.
2.1 Brominated flame retardant
Since their introduction, brominated flame retardants have become popular due to their high fire resistance and are indispensable to other flame retardants in some products. Currently, brominated flame retardants include high bromine monomers, elemental compounds, polymerizable polymers, and other types. The main varieties are shown in Table 2-1:
2-1 Main types of brominated flame retardants
The flame retardant mechanism of brominated flame retardants includes gas phase flame retardancy, free radical scavenging, oxygen barrier, heat absorption, and char formation. It can trap reactive free radicals (such as OH·, O·) during combustion. chain reaction with formation of inert combustible substances, which can coat surface of combustible materials and act as a fire retardant.
2.2 Phosphorus-containing flame retardants
Phosphorus flame retardants can be divided into organic phosphorus flame retardants and inorganic phosphorus flame retardants.
2-2 main types of phosphorus flame retardants
Phosphorus-based flame retardants usually play role of flame retardants when gas phase and condensation coincide: on one hand, phosphorus-based flame retardants thermally decompose to release free radicals such as PO·, PO2·, and stop chain reaction; on other hand, phosphorus-based flame retardants The flame retardant is constantly heated and dehydrated to form a carbon substance, which coats surface of plastic substrate and insulates air, which prevents release of combustible gases. and reduces intensity of thermal feedback of flame with substrate.
2.3 Ammonium salt type inorganic flame retardant
In recent years, with implementation of my country's environmental protection policy, halogen-free flame retardants have attracted much attention because of their environmental friendliness and stable addition. The preparation of halogen-free flame retardants is simple and safe to produce. The main varieties are APP, MCA, MP, MPP, etc. When using such flame retardants, due to hydrophilic properties of ammonium salts, special attention should be paid to the water resistance or electrical properties of flame retardant products.
Flame retardant MCA
The fire retardant principle of this type of flame retardant consists primarily of a gas phase flame retardant supplemented with a condensed phase flame retardant, but when used in combination with other flame retardants, ammonium phosphate flame retardants generally provide good condensed phase fire retardancy.
2.4 Metal flame retardant
Metal compounds range from antimony oxide compounds originally used as brominated synergists to widely used magnesium hydroxide, aluminum hydroxide and molybdenum compounds with excellent smoke suppression properties. And field of flame retardant materials occupies a very important place.
The principle of metal hydroxide fire resistance is that after metal hydroxide is heated, a large amount of water vapor is formed, and a large amount of heat is absorbed during entire combustion process, thereby reducing possibility of ignition.
Third, use of a flame retardant
For a certain flame retardant plastic, it is very important how to choose a flame retardant material that is effective and cheap without affecting performance of original material. When developing a formula, the principles of combining primary and secondary flame retardants and synergy between flame retardants should be observed.
3-1 flame retardant suitable for each matrix resin
In short, flame retardant mechanisms of flame retardants are different. There are hundreds of varieties of flame retardants, and new flame retardants are still being developed. It is very important to choose right flame retardant.
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