Regarding combustion reactions and combustion mechanisms, flame retardants generally have the following types of flame retardant mechanisms: flame retardant mechanism:
① The flame retardant mechanism of condensed phase
At high temperatures, flame retardants form condensed phases on the surface of polymers, isolating air, preventing heat transfer, and reducing the release of flammable gases, thereby achieving flame retardancy.
② Mechanism of free radical capture
During the combustion process of polymers, the large production of free radicals HO · and H · promotes gas-phase combustion reactions. If we can capture and eliminate these free radicals, cut off the chain reaction of free radicals, we can control combustion and achieve flame retardancy.
③ Cooling mechanism
Flame retardants undergo endothermic dehydration, phase transition, decomposition, or other endothermic reactions, reducing the temperature of the polymer surface and combustion zone, preventing thermal degradation, and ultimately reducing the volatilization of flammable gases, ultimately disrupting the conditions that maintain the continuous combustion of the polymer, achieving the purpose of flame retardancy.
④ Non combustible gas mechanism
This type of flame retardant can decompose into a large amount of non combustible gases when heated, such as CO2, N2, NH3, H2O, HCl, HBr, etc. It can dilute combustible gases and dilute the concentration of oxygen in the combustion zone, preventing combustion from occurring.
⑤ Mechanism of synergistic effect
The compounding of flame retardants is a synergistic system that utilizes the interactions between flame retardants to improve flame retardancy.
Flame retardant is a very complex process, and in fact, many flame retardant systems have multiple flame retardant mechanisms at work simultaneously.
Ammonium polyphosphate: A phosphorus nitrogen system (an expanding flame retardant, where phosphides and nitrides form an expanding coke layer on the surface at high temperatures, serving as a thermal insulation and oxygen blocking protective layer. Nitrogen containing compounds act as foaming agents and coke reinforcing agents. Phosphorus provides an acid source (dehydrating agent) and interacts with resins to promote the formation of carbides. Nitrogen provides gas source (foaming agent), which can expand the system and promote the formation of carbonized layer, forming porous foam carbon.