Inorganic low-smoke halogen-free flame retardant is a kind of inorganic flame retardant material that does not release toxic and corrosive gases such as hydrogen halide during combustion and has low smoke generation, which is widely used in wire and cable, building materials, electronic appliances and other fields. Its main types and characteristics are as follows:
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First, hydroxide flame retardants
1. Aluminum Hydroxide (ATH)
Features:
The decomposition temperature is about 200-300℃, releasing crystal water to absorb heat and cool down, inhibiting combustion.
An alumina coating is formed to block oxygen and slow combustion.
Non-toxic, low smoke, low cost, but the amount of addition (usually more than 50%) will affect the mechanical properties of the material.
2. Magnesium Hydroxide (MDH)
Features:
The decomposition temperature is about 340-490℃, the heat absorption is higher than ATH, and the flame retardant efficiency is higher.
Magnesium oxide coating, high temperature, corrosion resistance, suitable for high temperature environment.
The smoke suppression effect is better than ATH, but there are also problems of large addition amount and poor dispersion.
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Second, borate flame retardants
1. Zinc borate (ZB)
Features:
Both flame retardant, smoke suppression, drip prevention function.
When burned, a glassy borate layer is formed, which isolates oxygen and inhibits smoke generation.
With ATH, MDH and other synergistic use can improve the flame retardant efficiency.
2. Calcium borate, sodium borate
Features:
The flame retardant mechanism is similar to zinc borate, but the application is relatively few.
It is often used in special flame retardant systems or in combination with other flame retardants.
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Third, metal oxide flame retardants
1. Antimony trioxide (Sb₂O₃)
Features:
Traditional flame retardant synergists are often used in combination with halogen-based flame retardants (such as bromides).
When used alone, the flame retardant effect is limited, but it can significantly improve the efficiency of other flame retardants.
Antimony-containing compounds may produce toxic gases, and the amount should be strictly controlled.
2. Magnesium oxide (MgO), Alumina (Al₂O₃)
Features:
As ATH, MDH decomposition products, can be directly used as flame retardant filler.
Stable at high temperatures, enhance the mechanical properties and weather resistance of the material.
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Fourth, silicon flame retardant
1. Silicates (such as montmorillonite, kaolin)
Features:
Layered structure, can form a physical barrier, insulation heat and oxygen.
Endothermic decomposition releases water vapor, reducing the combustion temperature.
Both toughening, strengthening effect, improve material mechanical properties.
2. Nano Silica (SiO₂)
Features:
High specific surface area enhances carbonization and reduces smoke generation.
Improve the thermal stability and mechanical strength of the material.
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Fifth, phosphorus inorganic flame retardants
1. Red phosphorus
Features:
Highly effective flame retardant, but the color is dark, easy to absorb moisture, need microencapsulation treatment.
When burned, phosphoric acid is formed, which promotes carbon formation and blocks oxygen.
2. Ammonium polyphosphate (APP)
Features:
Containing phosphorus, nitrogen elements, both gas phase and condensed phase flame retardant.
When decomposed, ammonia is released, diluting the combustible gas and creating a phosphate coating.
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Sixth, other inorganic flame retardants
1. Expandable Graphite (EG)
Features:
Heat expansion to form a porous carbon layer, heat insulation, oxygen insulation.
Low smoke, non-toxic, suitable for sealing materials and fire retardant coatings.
2. Zinc stannate, ammonium molybdate
Features:
Synergistic flame retardant, with ATH, MDH, etc. can improve the flame retardant efficiency.
Inhibit smoke generation and improve material processing performance.
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Advantages of inorganic low smoke halogen-free flame retardants
Environmental protection: does not release hydrogen halide and other toxic gases, in line with environmental regulations.
Low smoke: the amount of smoke generated during combustion is low, reducing the harm to personnel and equipment.
Thermal stability: does not decompose at high temperatures, suitable for long-term high temperature environment.
Low cost: a wide range of raw materials, the price is relatively low.
Application field
Wire and cable: replace halogenated flame retardants, improve safety.
Building materials: Used for fire-proof board, insulation materials, etc.
Electronic appliances: as a circuit board, shell flame retardant filler.
Transportation: Used for automotive, high-speed rail interior materials.
Development trend
Nanometer: Through nanotechnology to improve the dispersion and efficiency of flame retardants.
Compounding technology: A variety of flame retardants are used together to reduce the amount of a single flame retardant.
Surface modification: improve the compatibility of flame retardants and substrates, and improve the mechanical properties of materials.
Inorganic low smoke halogen-free flame retardants are gradually becoming the research and application hotspot in the field of flame retardants because of their environmental protection and high efficiency.
