Halogen-free flame retardants refer to all flame retardants or flame retardant systems that do not contain halogens. The main components of halogen-free flame retardants are diverse and can be summarized into the following categories:
First, inorganic substances
Metal oxides: such as magnesium oxide, aluminum hydroxide (Al(OH)_3), magnesium hydroxide (Mg(OH)_2), etc. These substances can form a stable inorganic layer during the combustion process, isolating oxygen, so as to achieve a flame retardant effect. Magnesium hydroxide, in particular, is considered an environmentally friendly green flame retardant because of its low smoke, non-toxic, and can neutralize acidic and corrosive gases in the combustion process.
Silicates: such as silicates containing boron, etc., also has good flame retardant properties.
Other inorganic substances: such as sodium sulfide, potassium chloride, etc., although not the mainstream halogen-free flame retardant components, but in some specific applications are also used.
Second, organic species
Phosphorous flame retardants: such as ammonium polyphosphate (APP), phosphate ester, phosphonate ester, and phosphine oxide. Phosphorous flame retardants decompose to produce phosphoric acid, metaphosphoric acid and other phosphorous compounds when heated, these compounds have strong dewater, which can dehydrate and carbonize the polymer surface to form a carbon layer, so as to isolate oxygen and achieve the purpose of flame retarding.
Nitrogen flame retardants: organic compounds containing nitrogen, such as melamine, can release nitrogen and other inert gases during combustion, diluting the oxygen concentration in the combustion area, thereby inhibiting combustion.
Intumescent flame retardants: such as expandable graphite, etc., this type of flame retardant will expand to form a porous carbon foam layer when heated, isolating oxygen to achieve the purpose of flame retardancy.
Third, natural plant extracts
Certain natural plant extracts are also used as halogen-free flame retardants, such as soy protein complex additives made from oleic acid extracted from soybeans. This kind of flame retardant has the advantages of non-toxic and harmless, and can replace part of the production process of PVC plastic products, and is widely used in food packaging and other fields.
Fourth, nanoscale polymer composite materials
The halogen-free formulations with natural rubber as matrix and nano-sized polymer composite as main components also have good flame retardant properties. This kind of product not only has good water resistance and heat resistance, but also can form a stable inorganic layer or carbon layer during the combustion process to isolate oxygen and achieve the purpose of flame retardant.
In addition, there are some special halogen-free flame retardants, such as boron series flame retardants (such as zinc borate), etc., which achieve flame retardant effect by promoting the formation of carbon layers.
In summary, the main components of halogen-free flame retardants are diverse, including inorganic substances, organic substances, natural plant extracts and nanoscale polymer composite materials. These components can inhibit combustion through various mechanisms in the combustion process, so as to achieve the purpose of flame retardant.
