1. Inorganic flame retardant:
Inorganic flame retardants play a flame retardant role, mainly by the large specific volume of filler thermal storage and thermal conductivity properties. This can make the material is not easy to reach the decomposition temperature, or else the flame retardant will absorb heat when heat decomposition, and then slow down or stop the process of the main material temperature rise. Its flame retardant principle is that when heated, it releases crystalline water, which then evaporates, decomposes, and releases water vapour. In this reaction process, the need to absorb a lot of thermal energy generated by combustion, which can greatly reduce the surface temperature of the material, so that the possibility of thermal decomposition and combustion of polymer materials is greatly reduced.
2. Halogenated flame retardants:
Halogenated flame retardants is now one of the world’s largest production of organic flame retardants, used more halogenated flame retardants containing bromine and chlorine. Most of the halogenated flame retardants are organic, and the main polymer materials can be well integrated together. Halogenated flame retardants as flame retardant additives, will not fundamentally change the physical and chemical properties of the polymer material itself. Moreover, the amount of halogenated flame retardants added is very small, but can have a particularly good flame retardant effect. Halogenated flame retardants containing bromine are aliphatic, alicyclic, aromatic compounds containing bromine, such as decabromodiphenyl ether, decabromodiphenylethane and tetrabromobisphenol A. Chlorinated flame retardants are mainly chlorinated paraffins. Bromine and chlorine flame retardant principle is almost the same: when the temperature is very high, halogen flame retardants in the carbon-halogen bond will be broken, the release of halogen radicals, can be very good to catch the polymer material because of heat degradation of those free active radicals, can reduce the concentration of free radicals, so that it can slow down or stop combustion of the free radical chain reaction. In addition, the hydrogen halide released during decomposition of halogenated flame retardants does not burn easily, and can block oxygen, which also inhibits the combustion reaction. However, if the polymer material with halogenated flame retardants burns, it will produce a lot of hydrogen halide gas. This gas is toxic and corrosive, it is easy to absorb moisture in the air into a very corrosive hydrohalic acid, there will be a lot of smoke. These fumes, toxic gases and corrosive gases are harmful to human health, but also to extinguish the fire, escape and the subsequent recovery work to bring a particularly big trouble.
3.Treated Al(OH)3 flame retardant.
Aluminium hydroxide is also called aluminium oxide trihydrate (ATH), its molecular formula is Al(OH)3, is one of the inorganic flame retardants appeared very early, can play a synergistic effect with a lot of things, and non-toxic and non-corrosive. The use of aluminium hydroxide flame retardants now exceeds 80% of the total inorganic flame retardants, and they are widely used in a variety of polymer plastic products. The addition of aluminium hydroxide to polymer materials reduces the concentration of flammable polymers. When the polymer material is heated (about 250℃), the aluminium hydroxide will have a dehydration reaction and can absorb a lot of heat energy, which can effectively prevent the polymer material from increasing in temperature. At the same time, the decomposed water vapour reduces the concentration of flammable gases and oxygen produced by combustion and prevents the combustion from spreading. At the same time the decomposition of another metal oxide aluminium oxide (Al2O3) because of high catalytic activity, can make the polymer thermal cross-linking reaction accelerated, in the polymer surface to form a layer of carbonized film, this layer of film can effectively slow down the combustion when the heat transfer, so that play a role in flame retardant. Aluminium oxide can also adsorb particles, can not let the smoke out. Generally speaking, the more aluminium hydroxide is added, the better the flame retardant effect, but if too much is added, the strength of the polymer material will be greatly reduced. Another disadvantage of aluminium hydroxide is that the decomposition temperature is relatively low, between 245 and 320 ℃ will have a dehydration reaction, so the addition of flame retardant aluminium hydroxide also limits the processing temperature of polymer materials.
4. Phosphorus flame retardants.
According to the characteristics and composition of phosphorus flame retardants, they can be divided into inorganic phosphorus flame retardants and organic phosphorus flame retardants. Here, inorganic phosphorus flame retardant has red phosphorus, ammonium phosphate, ammonium polyphosphate, organic phosphorus flame retardant has phosphate ester, phosphite and so on. Phosphorus flame retardant is also a kind of high efficiency, very stable, widely used flame retardant, its flame retardant principle is mainly through the formation of isolation film to achieve the flame retardant effect. There are two different methods for the formation of barrier film: (1) when the flame retardant effect is exerted on oxygen-containing polymers: the thermal degradation of the flame retardant produces something that can make the surface of the polymer dehydrate and carbonise very quickly, and then form a carbonised layer. Because the monolithic carbon does not experience the kind of evaporative combustion and decomposition combustion that produces flames, it acts as a flame retardant. The chemical reaction that occurs internally is the thermal decomposition of phosphorus-containing compounds, and the final product is poly(metaphosphoric acid), which is a very strong dehydrating agent. (2) Phosphorus flame retardant in the combustion temperature will decompose into non-volatile glass-like material, it can be wrapped up the polymer surface, this tight protective layer can play the role of the isolation layer. The organophosphorus flame retardant works mainly in the decomposition stage of polymer materials at the beginning of the fire. It can promote the polymer material dehydration carbonisation, so that the polymer material can not produce flammable gases, and because the non-volatile phosphorus compounds play the role of coagulant, so that the charcoal compounds form a protective carbon film, the outside air and heat are isolated.
5.Silicon flame retardant.
Silicone flame retardant has inorganic silicon and silicone, inorganic silicon dioxide, silica, silicate, talc and so on, this kind of flame retardant is often used as a filler; silicone flame retardant is a newly appeared without halogen elements of the flame retardant, but also a kind of inhibition of the smoke produced by the charcoal agent, mainly refers to silicone resins, polysiloxanes (such as silicone oil, silicone resin, silicone rubber and a variety of silicone copolymers and so on), Polysilanes and so on, the fastest growing one is polysiloxane. Its flame retardant mechanism is mainly manifested in the condensed phase flame retardant mechanism, that is, through the generation of cracked carbon layer and improve the antioxidant capacity of the carbon layer to achieve the flame retardant effect. After adding organosilicon flame retardants to polymer materials, most of the organosilicon flame retardants will move to the surface of the material, and react at high temperature to form a silicate layer containing carbon on the surface of the polymer, which can play a role in slowing down or preventing flammable gases from escaping and the generation of free radicals. At the same time, the flame retardant can also promote the polymer into carbon, which can reduce the degradation rate of the polymer, so that it is not easy to thermal decomposition at high temperatures. On the other hand, silicone-based flame retardants will also undergo thermal decomposition by heat, this process must absorb a lot of heat, which can make the flame retardant material to slow down or stop heating.