The working principle of intumescent low smoke zero halogen flame retardants is mainly based on the formation of a porous carbon layer when the material is heated, and flame retardancy is achieved through the combined effect of physical and chemical actions. The specific process is as follows:
Flame retardant composition and reaction stage
Intumescent flame retardants are typically composed of three parts: acid source (dehydrating agent), carbon source (carbonizing agent), and gas source (foaming agent). Their working process is divided into the following key stages:
Low-temperature dehydration stage: At around 150℃, the acid source (such as ammonium polyphosphate) decomposes to produce inorganic acids, which act as dehydrating agents and undergo esterification reactions with the carbon source (such as pentaerythritol).
Medium-temperature foaming stage: The reaction system melts at 200-300℃, and the esterification reaction generates phosphate ester polymers. Meanwhile, the gas source (such as melamine) decomposes to produce non-flammable gases like ammonia, causing the system to expand and foam.
High-temperature carbonization stage: Polyols and esters continue to dehydrate and carbonize, forming inorganic substances and carbon residues. The system further expands and solidifies, ultimately forming a porous foam carbon layer.
2. Carbon layer flame retardant mechanism
The porous foam carbon layer achieves flame retardancy through the following mechanisms:
Thermal insulation effect: The carbon layer has a low thermal conductivity, which can effectively reduce the surface temperature of the material and delay thermal degradation.
Oxygen isolation effect: The dense structure of the carbon layer can prevent oxygen from entering the material interior and inhibit the combustion reaction.
Smoke suppression effect: The carbon layer can adsorb the smoke particles produced by combustion, reducing smoke release.
Anti-dripping function: The carbon layer can fix the molten material and prevent secondary combustion caused by dripping.
3. Typical reaction examples
Take the classic intumescent flame retardant system composed of ammonium polyphosphate (APP), pentaerythritol (PER) and melamine (MEL) as an example:
Reaction equation:
APPΔ H3 PO4 +NH3 ↑H3 PO4 +PER→ Phosphate ester polymer + H2O ↑MELΔ NH3 ↑+ Other gases Result: The generated porous carbon layer can increase the oxygen index (LOI) of the material to more than 30%, while significantly reducing the smoke density.
4. Advantages and Applications
Intumescent flame retardants have the following advantages:
Environmental friendliness: Halogen-free and no corrosive gas is produced when burning.
High efficiency: High flame retardant efficiency and low addition amount (usually 15-30%).
Multi-functionality: It simultaneously has the functions of heat insulation, oxygen isolation, smoke suppression, and anti-dripping.
This type of flame retardant is widely used in materials such as polypropylene (PP), polyethylene (PE), and epoxy resin, and especially has significant application value in fields such as wires and cables, building materials, and electronic appliances.
