Technical Principles and Mechanisms of Action
The mechanisms of action for flame retardants are primarily categorized into four types:
Gas-phase flame retardancy: Flame retardants decompose at high temperatures to produce inert gases (such as carbon dioxide or nitrogen), which dilute the concentration of combustible gases and interrupt the combustion chain reaction. For instance, phosphoric anhydride generated by the decomposition of phosphorus-based flame retardants can scavenge free radicals involved in combustion.
Condensed-phase flame retardancy: Flame retardants form a char layer on the material's surface, acting as a barrier against oxygen and heat transfer. Inorganic flame retardants (such as aluminum hydroxide and magnesium hydroxide) lower the material's temperature through endothermic decomposition while simultaneously forming a protective layer of aluminum oxide or magnesium oxide.
Heat-exchange interruption: Flame retardants promote the melting and dripping of the material, thereby carrying away heat and removing the source of combustion. This mechanism is commonly observed with low-molecular-weight organic flame retardants.
Synergistic flame retardancy: Multiple flame retardants are used in combination, leveraging complementary mechanisms to enhance overall effectiveness. For example, phosphorus-nitrogen synergistic systems can function in both the gas phase and the condensed phase simultaneously.
Application Scenarios and Industry Demands
Flame retardants are widely used in sectors such as construction, electronics, transportation, and textiles:
Construction materials: Flame retardants are incorporated into fire-resistant coatings, insulation boards, and cable sheathing to meet standards such as the *Code for Fire Protection Design of Buildings*. For example, external wall insulation materials for high-rise buildings must meet the Class B1 flame retardancy standard.
Electronics and electrical appliances: Components such as circuit boards, connectors, and plastic housings require flame retardants to prevent fires caused by short circuits. The EU's RoHS directive imposes strict regulations regarding the flame-retardant properties of electronic products.
