Brief discussion on the high status of bromine series in classification of polypropylene flame retardants
- time:
- 2019-05-11
There are many kinds of flame retardants for polypropylene, which can be classified into two categories according to their chemical composition: organic flame retardants and inorganic flame retardants, and reactivity and additivity according to their application methods. The representative flame retardants are bromine, phosphorus-nitrogen, phosphorus and aluminium hydroxide, magnesium hydroxide and so on.
1. Brominated flame retardants
Because of the low bond energy of C-Rr bond, most brominated flame retardants will decompose at 200-300 C, which is also the decomposition temperature range of polypropylene. Therefore, when polypropylene is decomposed by heat, brominated flame retardants also begin to decompose and capture the free radicals generated by the decomposition reaction, thus delaying or terminating the chain reaction of combustion. At the same time, the released HBr is a kind of non-combustible gas, which has a high density and can cover the surface of the material, play a role in blocking the surface of combustible gas, and also inhibit the combustion of the material.
Brominated flame retardants play an important role in the flame retardant application of polypropylene. At present, the main products are decabromodiphenyl ether, tetrabromobisphenol A, tetrabromopentaerythritol, brominated polystyrene, PENTABROMOTOLUENE and hexabromocyclododecane. The main disadvantage of brominated flame retardants is to reduce the anti-ultraviolet stability of the flame-retardant substrates, and produce more smoke, corrosive gases and toxic gases during combustion, which limits their application to a certain extent.
2. Phosphorus-Nitrogen Flame Retardants
Phosphorus nitrogen flame retardants are also called intumescent flame retardants. Polymers containing such flame retardants can produce a uniform layer of carbon foam when heated, which can resist heat, oxygen and smoke, and prevent droplets from occurring. Therefore, it has good flame retardancy. Phosphorus-nitrogen flame retardants have the advantages of halogen-free, low smoke and low toxicity.
Intumescent flame retardants generally consist of three parts: acid source (dehydrating agent), carbon source (carbonizing agent) and gas source (nitrogen source and foaming source). Intumescent flame retardant mainly acts as flame retardant in the condensed phase by forming porous carbon layer.
3. Phosphorus flame retardants
Phosphorus flame retardants play a flame retardant role in promoting the dehydration and dicarbonization of polymers at the initial decomposition stage. This dehydration and carbonization process must rely on the oxygen-containing groups of polymers themselves. For polymers with oxygen-containing groups of their own structure, their flame retardant effect will be better. For polypropylene, the flame retardant effect is not good when phosphorus flame retardant is used alone because its molecular structure has no oxygen-containing group, but if it is mixed with (OH) 3 and Mg (OH) 2, it can produce synergistic effect, thus obtaining good flame retardant effect.
Commonly used organophosphorus flame retardants are triphenyl phosphate, trimethylphenyl phosphate and tri (xylene) phosphate.
Propylene phosphate, butylbenzene phosphate, etc. Phosphates have dual functions of flame retardant and plasticizer. It can make flame retardant halogen-free, and its plasticizing function can improve the flow processability of plastic forming, and inhibit the residue after combustion. Toxic gases and corrosive gases are less than halogen flame retardants. Its main advantages are high efficiency, less influence on light stability or the role of light stabilizer, less corrosiveness in processing and combustion, hindering re-ignition, and little or no increase in the quality of dehydrating agent. However, most phosphate flame retardants also have some shortcomings, such as poor heat resistance, high volatility, poor compatibility, and droplets generated during combustion.
The main products of phosphorus-containing inorganic flame retardants are red phosphorus flame retardants, ammonium phosphate, ammonium polyphosphate and so on. With the increase of the amount of halogen-free flame retardant materials, the amount of red phosphorus flame retardant is also increasing. The flame retardant effect of red phosphorus is better than that of phosphate esters. Phosphorus-containing inorganic flame retardant has been widely used because of its good thermal stability, non-volatilization, non-generation of corrosive gases, lasting effect and low toxicity.
4. Aluminum hydroxide AL(OH)3(ATH)
It decomposes between 200 and 300 degrees C and absorbs 1967.8j/g of heat. It is a flame retardant with three functions: flame retardant, smoke suppression and filling. It has the advantages of non-toxic, non-corrosive, good stability, non-volatile, no toxic gases produced at high temperature, and low price, wide sources. However, as a flame retardant, it also has the disadvantages of large filling volume, poor mechanical properties and poor processability. The temperature at which AL (OH) 3 begins to decompose is in the process of polymer transformation from condensation to liquid phase, so it plays an important role in inhibiting the early temperature rise of polymer materials. When the mass fraction of AL (OH) 3 is 40%, the thermal decomposition rate of the material can be significantly slowed down, which has the effect of flame retardant and smoke reduction.
5. Magnesium hydroxide
Magnesium hydroxide decomposes at 340-490 (?) C with 782.9j/g heat absorption. It has good thermal stability, good flame retardant and smoke suppression effect, and is especially suitable for polypropylene materials with higher processing temperature. When Mg (OH) 2 is used in PP (the addition is more than 50%), it has good flame retardant effect, which is superior to AL (OH) 3. Under the same filling amount, the flame retardant effect of different ratios of aluminium hydroxide and magnesium hydroxide is not obvious, but the effect of two kinds of composite use is better than that of single use, because although both are dehydration reactions, there are differences in decomposition temperature and heat absorption. Magnesium hydroxide needs to be dehydrated at a higher temperature and has carbonization effect. Magnesium dihydroxide absorbs less heat, because its effect of inhibiting material temperature rise is not as good as aluminium hydroxide. The combination of the two can complement each other, and its flame retardant performance is better than that of single use. However, Mg (OH) 2 also has some shortcomings, such as poor acid resistance, poor dispersion and compatibility. It is necessary to develop new varieties with good compatibility.
