Summary and introduction of flame retardant principles of plastic flame retardants

Plastics and their products are mostly flammable. In order to reduce the occurrence of fires, some flame retardants are often added to plastics to improve their flame resistance. This article describes in detail the flame retardant mechanism of flame retardants for reference.

1. Condensed phase flame retardant mechanism

At high temperatures, flame retardants form a condensed phase on the surface of the polymer, which isolates the air, prevents heat transfer, reduces the release of flammable gases, and achieves flame retardancy. There are two ways to form a condensed phase isolation film: one is that the flame retardant decomposes into a non-volatile glass-like substance at the combustion temperature, and it is coated on the surface of the polymer. This dense protective layer acts as an isolation film, such as Boron and phosphorus halide flame retardants have similar characteristics; the second is to use the thermal degradation products of the flame retardant to promote rapid dehydration and carbonization of the polymer surface to form a carbonized layer, and the use of elemental carbon does not produce flame evaporative combustion and decomposition combustion to achieve resistance The effect of flame protection, such as the flame retardant effect of phosphorus-containing flame retardants on oxygen-containing polymers.

2. Free radical capture mechanism

In the polymer combustion process, a large number of generated free radicals promote the gas-phase combustion reaction. If we can manage to capture and eliminate these free radicals and cut off the free radical chain reaction, the combustion can be controlled and the purpose of flame retardant can be achieved. The flame-retardant mechanism of halogen-based flame retardants falls into this category.

3. Cooling mechanism

The flame retardant undergoes endothermic dehydration, phase change, decomposition, or other endothermic reactions, which reduces the temperature of the polymer surface and the combustion area, prevents thermal degradation, thereby reducing the volatilization of flammable gases, and ultimately destroys the continuous combustion of the polymer. Conditions to achieve flame retardant purpose. Al(OH)3 and Mg(OH)2 and boron-based inorganic flame retardants are quite representative

4. Synergy mechanism

The existing flame retardants are compounded so that various mechanisms of action can work together to reduce the amount of flame retardants and achieve better flame retardant effects. For example, the synergistic use of antimony oxide and organic halide flame retardant can form a very effective flame retardant system. When it acts on burning combustibles, the organic halide releases hydrohalic acid or halogen, and then reacts with antimony oxide. Produce antimony trihalide or antimony halide (SbOX). These antimony compounds have a flame retardant effect. Among them, the product SbX3 has a great flame retardant effect. It can form an inert gas, reduce the contact of combustibles with oxygen, and make the carbon cover layer. ; SbX3 volatilizes into the flame at high temperature and decomposes into various antimony compounds and halogen radicals, which change the chemical properties of the flame, consume the energy of the flame, and achieve the purpose of flame retardancy.