Types of fire retardant additivesHalogenated compounds:
These compounds release halogen radicals (e.g., chlorine or bromine) when heated, which interrupt the chemical reactions of combustion in the gas phase.
While highly effective, many have been phased out due to health and environmental concerns. Examples include Decabromodiphenyl Ethane (DBDPE) and Tetrabromobisphenol A (TBBPA).
Some are used with a synergist like antimony trioxide to enhance their efficiency.
Mineral-based compounds:
Aluminum trihydrate (ATH): This cost-effective additive releases water when heated, which cools the material and dilutes flammable gases.
Magnesium hydroxide (MH): Similar to ATH, but suitable for higher processing temperatures.
Huntite and Hydromagnesite: These minerals act by releasing carbon dioxide and water endothermically, providing a cooling and gas-diluting effect.
Phosphorus-based compounds:
These can work in both the solid and gas phases to inhibit combustion.
In the solid phase, they can form a protective char layer, while in the gas phase, they can trap radicals to quench the flame.
Examples include:
Ammonium polyphosphate (APP): Often used in intumescent systems, which swell to form an insulating char.
Organophosphates: Such as resorcinol bis(diphenylphosphate) (RDP), are used in various polymers.
Intumescent systems:
These additives form an insulating, protective char layer when exposed to heat.
They typically consist of three components:
An acid source (e.g., APP).
A carbonizing agent.
A blowing agent (e.g., melamine).
These work particularly well in plastics and are often halogen-free.
Nitrogen-based compounds:
Melamine and its derivatives are commonly used and have a synergistic effect with phosphorus compounds.
They work by releasing non-flammable gases, such as ammonia, which dilutes the concentration of flammable gases.
How they workFire retardant additives use several mechanisms to suppress fire:
Endothermic degradation: Some compounds, like mineral hydroxides, break down and absorb heat, cooling the material.
Gas phase radical quenching: Halogenated additives release chemicals that interfere with the free radical chain reactions in a flame.
Thermal shielding (solid phase): Intumescent additives form a char layer that acts as a thermal barrier, slowing heat transfer.
Dilution of gas phase: The release of non-combustible gases, such as water vapor from mineral hydroxides, dilutes the concentration of flammable gases.
ApplicationsFire retardant additives are used across a wide range of industries:
Electronics: Circuit boards, electrical casings, and wiring.
Construction: Insulation, textiles, and piping.
Transportation: Automotive interiors and components.
Consumer products: Furniture, textiles, and mattresses.
