Halogen-free flame retardants mainly include the following aspects:
1. Inorganic flame retardants
Metal oxides and hydroxides: such as aluminum oxide, aluminum hydroxide, magnesium hydroxide, etc. These substances can release water vapor when burning, absorb heat, reduce the combustion temperature, and form a protective layer on the surface of the material to isolate oxygen, so as to achieve flame retardant effect.
Boron flame retardants: such as zinc borate, calcium borate, etc. They can form a glassy borate protective layer during combustion to isolate oxygen, and boron can also promote the formation of carbon layer to improve flame retardant performance.
Silicate flame retardants: such as diatomite, montmorillonite and so on. They have high thermal and chemical stability, and can form a stable silicate protective layer during the combustion process, preventing the spread of fire.
2. Organic flame retardant
Phosphorous flame retardants: such as ammonium polyphosphate, phosphate ester compounds, etc. Phosphorous flame retardants can produce phosphoric acid, metaphosphate and other phosphorus-containing compounds during combustion. These compounds have strong dewatering ability, which can dehydrate and carbonize the polymer surface, form a carbon layer, isolate oxygen, and achieve flame retardant purpose.
Nitrogen flame retardants: such as melamine, guanidine salt, etc. Nitrogen flame retardants can release non-combustible gases such as nitrogen during combustion, diluting the oxygen concentration in the combustion area, thus inhibiting combustion.
Expansive flame retardants: This is a special class of organic flame retardants, usually composed of three parts: carbon source, acid source and air source. During combustion, they can cooperate with each other to form an expanded carbon layer, isolate oxygen, and release non-combustible gases to achieve flame retardant and smoke suppression effects.
3. Natural flame retardants
Plant extracts: such as some plant fibers, vegetable oils, plant wax, etc., have natural flame retardant properties. They can be extracted physically or chemically for the preparation of halogen-free flame retardants.
Natural minerals: such as graphite, talc powder, etc., also have certain flame retardant properties. They can be used directly as flame retardants or in combination with other flame retardants.
4. Compound flame retardant
In order to obtain better flame retardant effect and comprehensive performance, two or more flame retardants are often used in combination. This compound flame retardant can give full play to the advantages of various flame retardants, make up for each other’s shortcomings, and improve the flame retardant efficiency and the overall performance of the material.
In summary, halogen-free flame retardants cover many aspects such as inorganic flame retardants, organic flame retardants, natural flame retardants and composite flame retardants. They provide effective flame retardant protection for various materials through different flame retardant mechanisms and modes of action.
