Which flame retardants are used in flame retardant nylon-Ammonium polyphosphate APP
Flame-retardant nylon is one of many modified varieties of nylon. It can be used in automobile ignition system components, solar photovoltaic cell components, home appliance plugs and sockets, electrical circuit breakers and so on. The flame retardant rating of nylon before modification is around UL94 V-2. By adding flame retardant to nylon for modification, the flame retardant rating after modification can reach UL94V-0.
The processing temperature of nylon is relatively high. For example, the melting temperature of PA6 is 230-280℃, and the temperature of reinforced PA6 is higher, which is 250-280℃. This requires the use of flame retardants with relatively good thermal stability. For example, iodine-based flame retardants with relatively small CI bond energy cannot be used if thermal stability is not good. At present, bromine-based flame retardant nylons are more commonly used Flame retardants, red phosphorus and melamine salts.
Brominated flame retardants are a kind of halogen flame retardants. Among the brominated flame retardants, decabromodiphenyl ether is the most widely used. It is often used with antimony compounds. The HBr released by decabromodiphenyl ether reacts with Sb2O3 to form SbOBr, and SbOBr releases Sb2O3 when heated. SbBr3 is the main bearer of the flame retardant effect. The entire process is blocked by heat absorption and gas dilution. The combustion mechanism is flame-retardant.
Halogen-free is now advocated because halogen-based flame retardants will cause environmental problems when they are flame-retardant. In any case, the halogen-free flame-retardant nylon in the future is definitely the best choice. The halogen-free options are mainly red phosphorus and melamine salts.
my country is a big country in phosphorus resources in the world, so red phosphorus has a great cost advantage, and its flame retardant efficiency is higher, which makes it more widely used. Red phosphorus is decomposed by heat to form phosphoric acid. On the one hand, phosphoric acid acts as a dehydrating agent and promotes carbon formation. The formation of carbon reduces the heat transfer from the flame to the condensed phase; on the other hand, phosphoric acid can absorb heat because it prevents the oxidation of CO to CO2 , Reduce the heating process. It is flame-retardant through endothermic and cohesive phase flame-retardant mechanism.
However, in 2010, the Panasonic recalled the door incident caused people to worry about the use of red phosphorus flame retardant, the reason is that red phosphorus will make the product performance there are certain potential safety hazards. On the other hand, the color of red phosphorus also makes it limited to dark nylon products such as black or red. Therefore, light-colored or transparent halogen-free flame-retardant nylon generally uses melamine salts.
Trigulation
Ammonium polyphosphate APP is also called ammonium polyphosphate or condensed ammonium phosphate (APP for short). Ammonium polyphosphate is non-toxic and tasteless, does not produce corrosive gas, has low moisture absorption and high thermal stability. It is a non-halogen flame retardant with excellent performance.
Ammonium polyphosphate is a polyphosphate containing N and P. According to its degree of polymerization, it can be divided into three types: oligomerization, medium polymerization, and high polymerization. The higher the degree of polymerization, the lower the water solubility, and vice versa. According to its structure, it can be divided into crystalline and amorphous. The crystalline ammonium polyphosphate is a long-chain water-insoluble salt. The general molecular formula of ammonium polyphosphate is (NH4)(n+2)PnO(3n+1), when n is 10-20, it is water-soluble; when n is greater than 20, it is poorly soluble.
Chemical properties
The phosphorus content of ammonium polyphosphate is as high as 30% to 32%, and the nitrogen content is 14% to 16%. The most prominent feature of this type of flame retardant is that the amount of smoke generated during combustion is extremely low and does not produce hydrogen halide. Because of its good thermal stability, ammonium polyphosphate can replace ammonium phosphate.
Ammonium polyphosphate is white crystalline or amorphous fine powder. The water solubility and hygroscopicity of APP decrease as the polymer increases. According to the different degree of polymerization n in China, it can be divided into water-soluble (n=10-20, relative molecular mass 1000-2000) and water-insoluble (n>20, relative molecular mass greater than 2000). n can be greater than 1000. In foreign countries, n<100 is called crystalline phase I ammonium polyphosphate (APPI), and the branched APP with n>1000 is called crystalline phase II ammonium polyphosphate (APPII). Short-chain APP with n<100 is more sensitive to water (hydrolyzability) than ultra-long-chain (M>1000) APP, and the latter has higher thermal stability and hydrolysis resistance. Long-chain APP begins to decompose into phosphoric acid and ammonia at a temperature above 300°C, while short-chain APP begins to decompose at a temperature above 150°C.
The commonly used crystalline APP is water-insoluble long-chain ammonium polyphosphate. APP has large phosphorus content and high nitrogen content. The phosphorus-nitrogen system produces a synergistic effect and has good flame retardancy. The relative density is small, the dispersion is good, the chemical stability is good, the smoke is suppressed, and the toxicity is low (Acute oral poisoning data (rat) LD50>10g/kg).
Features and uses
APP is widely used in intumescent fireproof coatings, polyethylene, polypropylene, polyurethane, epoxy resin, rubber products, fiberboard and dry powder fire extinguishing agent, etc. It is a safe and efficient phosphorus-based non-halogen smoke suppressant flame retardant, which belongs to expansion Flame retardant mechanism of type flame retardant.
APP has high flame retardancy, dimensional stability, hydrolysis resistance and heat resistance in rigid polyurethane foam. The amount of toxic and corrosive gas generated for rigid polyurethane foam is even comparable to similar materials that are not flame-retardant. The generation of carbon monoxide and hydrogen chloride is also much lower than that of halogen-containing polyurethane foam.
Ammonium polyphosphate has intumescent flame retardant function, so it is more conducive to smoke reduction and anti-dripping. Although it is solid, it is easy to disperse in polyol. Generally speaking, polyurethane components containing more polyester polyols are more suitable for flame retardant APP than polyether polyol components. The dosage is 5-20 parts.
APP is not only suitable for rigid polyurethane foam and polyester flexible polyurethane foam, but also other resins, adhesives and coatings. The cyanamide salts mainly include melamine cyanurate (MCA), melamine polyphosphate (MMP), etc., which have the advantages of low toxicity, low corrosivity, high flame retardant efficiency, and no conflict with additives. They can be used alone. Make PA reach UL 94 V-0 level.
After melamine salt is heated and decomposed, it will take away some heat and reduce the surface temperature of PA. From the perspective of gas phase analysis, decomposition easily releases non-combustible gases such as ammonia, nitrogen, nitrogen oxides, and water vapor, which dilute the concentration of combustible and combustion-supporting gases and hinder further combustion in the PA. From the perspective of the condensed phase, the degradation of PA material is advanced, which promotes the generation of carbon residue and protects the interior of the matrix.