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Flame Retardants: Mechanisms of Action

Flame retardants prevent or inhibit the physical and chemical changes in the combustion process of polymer materials. These effects are reflected in the following aspects:

1. Heat Absorption Effect

• Flame retardants decompose endothermically, absorbing heat from the combustion zone.
• Examples: Aluminum hydroxide (Al(OH)₃) and magnesium hydroxide (Mg(OH)₂) release water vapor upon decomposition, cooling the material.

2. Covering Effect

• A protective char or glassy layer forms on the polymer surface, shielding it from oxygen and heat.
• Examples: Phosphorus-based flame retardants promote char formation.

3. Dilution Effect

• Non-combustible gases (e.g., CO₂, H₂O, N₂) are released, diluting flammable gases and oxygen.
• Examples: Nitrogen-based flame retardants (e.g., melamine) release inert gases.

4. Inhibition Effect (Gas-Phase Radical Quenching)

• Flame retardants release free radical scavengers (e.g., Cl·, Br·) that interrupt the combustion chain reaction.
• Examples: Halogenated flame retardants (e.g., decabromodiphenyl ether) interfere with the fire cycle.

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