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Flame retardant 3
Intumescent flame retardants
Intumescent flame retardants are also halogen-free. Such flame retardants usually consist of three components.
- Polyphosphate, e.g., ammonium polyphosphate
- Carbon suppliers, e.g. dipentaerythritol
- Propellant, e.g. melamine, which gives off gaseous decomposition products when heated
In the heat, carbon-rich decomposition products are formed from the carbon suppliers and the polyphosphate, which are foamed into a highly viscous protective layer with the help of the gaseous decomposition products, e.g. of melamine.
The high amounts of additives (up to 40% by weight) necessary for adequate fire protection in the case of polystyrene are a disadvantage. This changes, or more precisely, other material properties deteriorate considerably.
Metal hydroxides such as aluminum and magnesium hydroxide split off water vapor in the heat, which reduces the oxygen concentration. Since the decomposition is endothermic, heat is also extracted from the combustion process.
In terms of quantity and in relation to all plastics, metal hydroxides are the most widely used flame retardants. However, they are not used in polystyrene because the amounts required are so high that the mechanical properties deteriorate significantly.