Red phosphorus is extremely flammable - the main raw material for making matches. It may seem inconceivable to use red phosphorus as a Flame Retardant, but red phosphorus is indeed an efficient flame retardant, especially in plastics; but in resins, red phosphorus and other phosphorus-containing flame retardants function The process is not a simple oxidation, and the phosphorus-containing flame retardant mainly acts in the condensed phase.
The flame retardant mechanism is:
①. Phosphoric acid is formed as a dehydrating agent, and promotes the formation of carbon. The formation of carbon reduces the heat conduction from the flame to the condensed phase, and can play an insulating role.
②. Phosphoric acid can absorb heat because it prevents the oxidation of CO to CO2 and reduces the heating process.
③.Form a thin glassy or liquid protective layer for the condensed phase, thus reducing oxygen diffusion and heat and mass transfer between gas and solid phases, inhibiting carbon oxidation process, reducing combustible substances and combustibles gas concentration.
④. The thermal decomposition of phosphorus-containing flame retardants changes as follows: phosphorus-based flame retardants→phosphoric acid meta→phosphoric acid→polymetaphosphoric acid, polymetaphosphoric acid is a stable compound that is not volatile and has strong dehydration. It is isolated from the air; the desorbed water vapor absorbs a lot of heat, and the flame retardant on the polymer surface is thermally decomposed to release volatile phosphides. The mass spectrometry analysis shows that the concentration of stored hydrogen atoms is greatly reduced, indicating that PO can also capture H, that is PO·+H·=HPO.
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