Brief Introduction of Related Knowledge of Phosphorus Flame Retardants
Phosphorus flame retardants play an important role in halogen-free flame retardants. According to their composition and structure, they can be divided into inorganic phosphorus and organic phosphorus flame retardants. The former is mainly red phosphorus and ammonium polyphosphate, while the latter is mainly phosphate and phosphonate. Red phosphorus is an excellent inorganic phosphorus flame retardant with high efficiency, smoke suppression and low toxicity. However, it is easy to absorb moisture, oxidize, emit highly toxic gases and explosive dust, which limits its application. Aluminum hydroxide, metal sulfate and synthetic resin are often used as wall materials to improve the properties of red phosphorus by microencapsulation.
Flame retardant experimenter
In the future, the development direction of red phosphorus surface treatment is as follows: firstly, by modifying the encapsulated materials to make them both heat stable, plasticizing and flame retardant, we can develop multi-functional microcapsulated red phosphorus flame retardant; secondly, we can study the effective compounding relationship between various flame retardants and red phosphorus flame retardant, and microencapsulate them to increase the flame retardant effect and improve the mechanical properties of materials; thirdly, red phosphorus has the function of thermal stability, plastic Smoke suppression effect, we can find a suitable smoke suppressant to compound with it, promote the development of smoke suppression technology, because smoke suppression in fire is more important than fire prevention. Ammonium polyphosphate (APP) is also a kind of inorganic phosphorus flame retardant with good performance. It is an active research field of phosphorus flame retardants at present. App's P-N flame retardant element content is high, thermal stability is good, the product is nearly neutral, in addition, cheap, low toxicity, flame retardant performance is durable, can be used alone or in combination with other flame retardants for plastic flame retardant. At high temperatures, APP rapidly decomposes into ammonia and polyphosphoric acid, which can dilute the oxygen concentration in the gas phase, thus preventing combustion. In addition, polyphosphoric acid is a strong dehydrating agent, which can make the polymer dehydrate and carbonize to form a carbon layer, isolate the contact between the polymer and oxygen, and prevent combustion in the solid phase. Organophosphorus flame retardants are one of the most important types of flame retardants. They have dual effects of flame retardant and plasticizing. They can completely realize halogenation-free flame retardant, improve the fluidity of plastic moulding, inhibit the residues after combustion, and produce less toxic and corrosive gases than halogen flame retardants. The flame retardant mechanism is as follows: on the one hand, the flame retardant is decomposed by heat to produce phosphoric acid, metaphosphoric acid and polymetaphosphatic acid. These substances have strong dehydration and carbonization, which can dehydrate and carbonize the polymer surface, while the elemental carbon can not produce flame evaporative combustion and decomposition combustion, so it has flame retardant effect; on the other hand, the flame retardant is heated to produce PO free radicals, which can absorb a lot of H and HO Thus the combustion reaction is interrupted. Phosphate flame retardant belongs to additive flame retardant. Because of its abundant resources and low price, it is widely used. Phosphates are prepared by the reaction of corresponding alcohols or phenols with phosphorus trichloride and hydrolysis. Phosphate flame retardants which have been successfully developed and widely used in the market are trimethylphenyl phosphate, triphenyl phosphate, triisopropyl phosphate, tributyl phosphate, trioctyl phosphate, tolyl diphenyl phosphate and so on. Phosphates have many kinds and wide uses, but most of them are liquid, heat-resistant and volatile, and their compatibility with polymers is not ideal.
Flame retardant
Phosphonate flame retardant is a promising flame retardant. Because of the C-P bond in the phosphonate molecule, it has very good stability, water resistance and solvent resistance. Foreign phosphonate products include: Pyrovatex developed by Giba-Geigy is N-hydroxymethylpropylamide methylphosphonate, and Antiblaze developed by Mobil is cyclic phosphonate. Phosphonates have also been studied in China. The synthesized phosphonates are N, N-p-phenylenediamine (2-hydroxy) dibenzylphosphonate tetraethyl ester and dimethyl methylphosphonate (DMMP), among which DMMP is an additive flame retardant developed in recent years. DMMP is prepared from trimethyl phosphite by isomerization reaction with catalyst and molecular rearrangement. The most remarkable characteristic of DMMP is that its phosphorus content is as high as 25%. The flame retardant effect is very good. When the amount of DMMP is half of the common flame retardant, it can play the same role.
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