As is well known, the essence of flame retardants is to prevent or slow down the effects of combustion factors through physical and chemical interactions. There are four factors for PA: heat source, air, combustibles, and free radical reactions.
Adding flame retardants is an important method to eliminate PA combustion conditions without changing the PA matrix. Different flame retardants have different flame retardant effect modes. According to the specific mode of action of flame retardants, they can be divided into condensed phase flame retardant mode, gas-phase flame retardant mode, and synergistic flame retardant mode.
1. Gas phase flame retardant method
Flame retardants play a role in inhibiting or interrupting the combustion reaction of combustible gas mixtures in the gas phase. There are two specific ways to achieve gas-phase flame retardancy:
One is that flame retardants undergo thermal decomposition to produce free radical scavengers, thereby interrupting free radical reactions and inhibiting the progress of combustion reactions;
The second is that flame retardants decompose upon heating, releasing inert gases that fill the vicinity of the combustion center, significantly diluting the concentration of oxygen and gas-phase combustibles near the combustion center, thereby suppressing combustion conditions and achieving flame retardant effects.
2. Condensed phase flame retardant mode
Condensed phase flame retardant refers to the flame retardant effect of the corresponding flame retardant mainly in the bonding component, thereby delaying or preventing the thermal decomposition process of the polymer, and thus playing a flame retardant role, inhibiting the combustion of the polymer. There are two specific ways for condensed phase flame retardancy:
One is that flame retardants undergo thermal decomposition during combustion, thereby absorbing a large amount of heat generated during combustion and preventing combustion from continuing;
The second is that flame retardants undergo chemical reactions at high temperatures, producing solid metal oxides (such as alumina, boron trioxide, magnesium oxide, etc.) or high-density vapors that can be covered with materials during combustion. The surface of polymer materials blocks the exchange of substances and energy between the polymer materials and the outside world, thereby suppressing the progress of combustion.
3. Collaborative flame retardant mode
In addition, some flame retardants have both gas-phase and condensed phase flame retardant mechanisms, playing a synergistic role in flame retardancy. Due to the fact that flame retardants act on the same gas phase and coagulation, the combustion of polymers is more inhibited.
Therefore, in terms of specific effects, flame retardants that play a synergistic flame retardant role can achieve more efficient flame retardant effects, thereby reducing the amount of PA flame retardant used.
