Classes of Flame Retardants
Flame retardants are generally classified according to their chemical makeup. The most common classes of flame retardants are: Brominated, Phosphorus, Nitrogen, Chlorinated and Inorganic.
Brominated compounds are used for a number of purposes, but the major use is as flame retardants. Bromine interacts with the fire cycle in the gas phase to stop the chemical chain reaction that leads to flame formation and a self-sustaining fire. In essence, brominated flame retardants either prevent a fire from starting in the first place, or significantly slow a fire down. Brominated compounds also can be added to materials like plastic without altering their properties. As a result, they can be used in many applications. Highly effective, brominated flame retardants are used in a variety of materials, including textiles, electronics, building materials, plastics and foams. They are often used in combination with an antimony trioxide synergist.
Flame retardants containing phosphorus interrupt the combustion process by promoting “charring.” In the presence of a heat source, phosphorus flame retardants release phosphoric acid which causes the material to char and form a thick glassy layer of carbon. This carbonated char stops the decomposition process (pyrolysis) and prevents the release of flammable gases, essentially cutting off fuel to the flame. It also provides a barrier between the material and the heat source. Phosphorus flame retardants are used in some upholstered furniture, foam mattresses, textiles, television casings, rubber and plastics.
Nitrogen flame retardants work in several key ways to provide fire protection. At high temperatures, they enable the formation of stable molecular compounds that stop the decomposition process (pyrolysis) and prevent the release of flammable gases. They also release inert nitrogen gases that inhibit the chain reaction leading to combustion, and can act as a synergist when combined with phosphorus to reinforce their flame retardant functions. Nitrogen flame retardants are used in insulation, furniture foams and electronics.
Like bromine-based flame retardants, chlorinated flame retardants interact with the fire cycle to stop flame formation. They are used in some polyurethane foam, rubber and flexible plastics.
A variety of inorganic compounds, most notably hydrated aluminum and magnesium oxides, are used as flame retardants, or, as is the case with antimony trioxide, as part of a flame retardant system in conjunction with bromine, phosphorus or nitrogen flame retardants. These flame retardants slow down the decomposition process and the release of flammable gases that fuel the combustion process, release inert gases that interrupt the chemical chain reaction that produces flames and produce a non-flammable and resistant layer on a material’s surface, reducing the release of flammable gases. Inorganic flame retardants are used in some plastics, paints, adhesives, rubber, textile back coatings, wire and cable.