Flame retardants are additives used to improve the flame resistance of materials, prevent materials from being ignited and inhibit the spread of flames. Its history of use can be traced back to 1820. Today, flame retardants have developed into the second largest additive after plasticizers.
The polymer flame retardants that have been developed and applied at present mainly contain N, P, As, Sb, Bi of group VA and CI and Br of group VII A, as well as Al, B, Zn, Sn, Mg, Ca, etc. compound of. Among them, the most commonly used and most effective are compounds containing P, CI, Br, Sb and Al.
1. Classification according to flame retardant elements contained
According to the flame retardant elements contained, flame retardants can be divided into halogen series, phosphorus series, nitrogen series, sulfur series, phosphorus-halogen series, phosphorus-nitrogen series, silicon series, antimony series, boron series and aluminum-magnesium series. Flame retardants, among which halogen flame retardants are currently one of the most produced flame retardants in the world. They have the characteristics of low addition amount and significant flame retardant effect, and occupy an important position in the field of flame retardancy.
2. Classification according to the use method of flame retardants
According to the different usage methods of flame retardants, flame retardants can be divided into two categories: reactive type and additive type.
(1) Reactive flame retardant
Reactive flame retardants refer to flame retardants that have reactive functional groups in the molecule that can participate in the reaction during the polymer synthesis process and be incorporated into the polymer molecules. Its advantages are good stability, long-lasting flame retardant effect, low toxicity, and little impact on plastic properties. It can be considered an ideal flame retardant. The disadvantage is that it is inconvenient to apply and there are few varieties. The current usage only accounts for about 10%-20% of flame retardants. Reactive flame retardants are mainly used in thermoset plastics and sometimes in thermoplastics. Some reactive flame retardants can also be used as additive flame retardants.
(2) Added flame retardant
Additive flame retardants are flame retardants that are incorporated into plastics before processing and physically dispersed in the mixture. It is characterized by easy use and strong applicability. Its current usage accounts for 80%-90% of the entire flame retardant. The disadvantage is that while improving the flame retardancy, it reduces some inherent properties of the plastic itself, such as processability and mechanical properties. Added flame retardants are commonly used in thermoplastics.
3. Classification by flame retardant components
According to different flame retardant components, flame retardants can be divided into two categories: inorganic flame retardants and organic flame retardants.
(1)Inorganic flame retardant
There are many varieties of inorganic flame retardants, and different inorganic flame retardants have different functions.
Some show flame retardant effects when used alone, such as red phosphorus; some show flame retardant effects when used in combination with halogen-containing organic flame retardants, such as Sb₂O₃; some also act as fillers and can decompose crystal water to show flame retardant effects. of, such as aluminum hydroxide.
Inorganic flame retardants have the advantages of good thermal stability, non-toxicity, no corrosive gases, non-volatility, smoke suppression, long-lasting effect, and low price. The disadvantage is that it affects the processing and molding properties and physical and electrical properties of polymer materials. have negative impacts.
(2) Organic flame retardants
There are also many varieties of organic flame retardants, which are subdivided by compound type, mainly including phosphorus and halogen flame retardants. Phosphorus-based flame retardants can also be divided into halogen-free and halogen-containing flame retardants; and halogen-based flame retardants can also be divided into chlorine-based and bromine-based flame retardants.
Organic flame retardants, especially brominated organic flame retardants, have good flame retardant effects, small dosage, and little impact on the performance of plastic products. Therefore, despite their toxicity, high smoke generation and the release of highly corrosive halogenated Hydrogen gas and other issues are still an important flame retardant that is widely used.