Halogen flame retardants include bromine and chlorine flame retardants. Halogen flame retardants are currently one of the largest organic flame retardants in the world. Most halogen flame retardants are brominated flame retardants. Industrially produced brominated flame retardants can be divided into three categories: additive type, reactive type and polymer type, with a wide variety. There are more than 20 additive brominated flame retardants, more than 10 polymer brominated flame retardants, and more than 20 reactive brominated flame retardants on the domestic and foreign markets. Additive flame retardants mainly include decabromodiphenyl ether (DBDPO), tetrabromobisphenol A, and bis(2,3-dialkylpropyl) ether (TBAB), octabromodiphenyl ether (OBDPO ), etc.; reactive flame retardants mainly include tetrabromobisphenolA（TBBPA), 2, 4, 6-Tribromophenol, etc.; polymer flame retardants mainly include brominated polystyrene, brominated epoxy resin, tetrabromobisphenolAcarbonate oligomer, etc.
The main reason why brominated flame retardantsare favored is their high flame retardant efficiency and affordable price. Due to the low bond energy of the C-Br bond, most brominated flame retardants decompose at temperatures between 200°C and 300°C. This temperature range is also the decomposition temperature range of commonly used polymers. Therefore, when the polymer decomposes, the brominated flame retardant also begins to decompose and can trap free radicals when the polymer material decomposes, thereby delaying or inhibiting the reaction of the combustion chain, and the released HBr itself is a flame retardant gas . It can cover the surface of materials to block and dilute the oxygen concentration. This type of flame retardant is used without exception with antimony (antimony trioxide or antimony pentoxide) to significantly improve the flame retardant effect through synergy.
Halogen flame retardants mainly play a flame retardant role in the gas phase. The hydrogen halide gas produced due to the decomposition of halides is a non-flammable gas and has a diluting effect. It has a large specific gravity and forms an air film on the solid surface of the polymer material, which can isolate air and heat and play a covering role. More importantly, hydrogen halide can inhibit the chain reaction of polymer material combustion and play a role in scavenging free radicals.
The bromine-containing flame retardant added to the polymer material will decompose and react to generate free radicals Br· when exposed to fire or heat, and the free radicals will react with the polymer material to generate Hydrogen bromide, hydrogen bromide and highly active OH·free radicals on the one hand regenerate Br, on the other hand reduce the concentration of OH·free radicals, thereby inhibiting the combustion chain reaction and slowing down the combustion speed until it is extinguished.
However, once a fire occurs, these substances decompose and burn to produce a large amount of smoke and toxic and corrosive gases, causing “secondary disasters”. The combustion products (halides) are released into the atmosphere Medium long life and difficult to remove. Once they enter the atmosphere. Seriously pollutes the atmosphere and destroys the ozone layer. In addition, the combustion and pyrolysis products of polybrominated diphenyl ether flame-retardant polymer materials contain toxic polybrominated dibenzodioxane (PBDD) and polybrominated dibenzofuran (PBDF).
