- Flame Retardants
The fire triangle demonstrates that three factors
must coincide in order for anything to burn.
The three factors mentioned above are related to each other in the combustion process: the combustion of plastics will be taken as an example in the following.
The combustion of plastics is a process comprising many steps and basically initiated by a heat source initiating the decomposition of the polymer. These two steps, heating and decomposition of the polymer consume energy (endothermic process) for overcoming the high binding energies between individual atoms (200 to 400 kJ/mole).
Combustible gases are formed, which mix the oxygen of the air and ignite. This leads to the exothermic part of the process, i. e. flame propagation and heat release. Pyrolysis of the polymer is reinfoced by thermal feedback (heat release), which fuels the flame at an increasing level. The flame is supported by extremely high energy H· and OH· radicals, which confer a high velocity to the flame.
Flame retardants may inhibit the chemical reactions in the flame by removing the high energy radicals, or initiate the formation of a charred layer on the surface. Thus, the polymer is protected against the attack of heat and oxygen of the air and prevents the formation of flammable gas mixtures.