Three Common Flame Retardants for PP Plastic

Flame retardants are a diverse and widely used chemical additive, commonly used to flame retard materials that are combustible or difficult to ignite. Let’s take a look at the three common flame retardants for PP plastic:

1.      Brominated flame retardants

Most rominated flame retardants decompose at 200-300°C, which is also the decomposition temperature range of polypropylene. Therefore, when polypropylene decomposes due to heat, brominated flame retardants also begin to decompose and can capture the free radicals generated by the degradation reaction, thereby delaying or terminating the chain reaction of combustion. At the same time, the released HBr itself is a non-flammable gas, which has a high density and can cover the surface of the material, blocking the surface combustible gas and inhibiting the combustion of the material.

The main disadvantage of brominated flame retardants is that they reduce the UV stability of the flame-retarded substrate, generate more smoke, corrosive gases and toxic gases during combustion, which limits their application.

2.      Phosphorus-nitrogen flame retardants

Phosphorus-nitrogen flame retardants, also known as intumescent flame retardants, can form a uniform carbonaceous foam layer on the surface of polymers when heated, providing insulation, oxygen barrier, smoke suppression and preventing dripping. Therefore, they have good flame retardant performance. The intumescent flame retardant system generally consists of three parts: acid source (dehydration agent), carbon source (carbonizing agent) and gas source (nitrogen source, foaming source). Intumescent flame retardants mainly play a flame-retardant role in the condensed phase by forming a porous foam carbon layer. Phosphorus-nitrogen flame retardants have the advantages of being halogen-free, low-smoke and low-toxicity.

3.      Phosphorus-based flame retardants

The flame-retardant effect of phosphorus-based flame retardants is due to dehydration and carbonization during the initial decomposition of polymers. This dehydration carbonization step must rely on the oxygen-containing groups in the polymer itself. For polymers with oxygen-containing groups in their structure, their flame-retardant effect will be better. For polypropylene, since its molecular structure does not contain oxygen-containing groups, when phosphorus-based flame retardants are used alone, the flame-retardant effect is not good. However, if it is compounded with (0H)3 and Mg(OH)2, a synergistic effect can be produced to achieve good flame-retardant effect.