How to Improve the Flame Retardancy of Nylon

Nylon polyamide (PA),) is a polymer containing amide-group (- NHCO-) in the main chain of the molecule, which is prepared by the condensation reaction of diamine and dicarboxylic acid. Density 1.15 g/cm3, including aliphatic PA, aliphatic-aromatic PA and aromatic PA. Among them, aliphatic PA has many varieties, large yield and wide application, and its name is determined by the specific carbon atom number of synthetic monomer.

 

The main varieties of PA are PA6,PA66,PA610,PA1010,PA11,PA12, which have the advantages of mechanical properties, wear resistance, chemical resistance, oil resistance and so on. But flammability of PA is the biggest obstacle to its application. In order to improve the flame retardancy of PA, a great deal of research has been done on the flame retardant modification of PA at home and abroad, and a variety of excellent products have been developed. The following are several ways to improve the flame retardancy of nylon.

 

1. Addition of nitrogen-based flame retardant

The main component of nitrogen-based flame retardant is melamine, which has the advantages of low toxicity, low corrosion, high flame retardant efficiency and no conflict with auxiliaries. The PA can reach UL 94 V-0 grade when used it alone. When the nitrogen flame retardant is decomposed, some heat will be taken away and the surface temperature of PA will be reduced. From the gas phase point of view, decomposition is easy to release ammonia, nitrogen oxides, water vapor and other non-gas, diluted flammable, combustible gas concentration, hindering the further combustion of PA. From the point of view of condensed phase, the degradation of PA materials was advanced, which promoted the formation of carbon residue and protected the inner matrix. Nitrogen series flame retardants are mainly melamine cyanurate (MCA), melamine polyphosphate (MMP), aminoguanidine sulfonate guanidine sulfonate (GAS).

 

2. Addition of phosphorous-based flame retardant

The flame-retardant effect of phosphorous flame retardant is mainly reflected in the initial combustion stage, the formation of oxygenated acid with boiling point up to 300 ℃, reduce the concentration of combustible gas produced by thermal decomposition of polymer, and the formation of carbon layer to insulate the external combustible gas and heat. It shows good flame retardant effect. Phosphorus flame retardant can be used as free radical trapping agent in gas phase, P- and PO- free radicals can be formed by combustion, OH and H can be trapped in the flame, and the concentration of combustible gas can be diluted to inhibit the flame. In the solid phase, a dense and continuous carbon layer was formed by catalyzing the formation of carbon by oxygen-containing acid, which acted as a barrier to the heat and the diffusion of the matrix degradation products to flame retardant. Organophosphorus flame retardant can also achieve excellent flame-retardant effect in combination with red phosphorus except being used alone.

 

3. Addition of inorganic flame retardant

Common inorganic flame retardants, such as aluminum hydroxide, calcium hydroxide, magnesium hydroxide, etc., are widely used in plastic flame retardant due to their advantages of non-toxic, low smoke and low cost.

 

The flame retardant mechanism is to absorb a large amount of heat in the combustion zone, so that the temperature of the combustion zone falls below the critical combustion temperature. High melting point metal oxide is produced by thermal decomposition, which is covered on the solid surface of combustion to form a protective layer and delay heat conduction. At the same time, the decomposition produces a large amount of water vapor, which can dilute the combustible gas and achieve the effect of flame retardancy. In addition to the common metal oxides, which can be used as inorganic flame retardants, the Burmstone (BM) has the same flame retardant principle. In recent years, nanotechnology has led to the development of flame retardant PA. The lamellar structure or the network structure formed by the nanomaterials can effectively block the combustion process and delay the escape of combustible and combustible gases.

 

4. Addition of reactive flame retardant

The reactive flame retardants are mostly aryl phosphine oxide derivatives, phosphate phenanthrene phosphate ester, 910-dihydro-10- [2O3-diketo-propyl] -10-phenanthrene 10-oxide and so on. They can participate in the polymerization of PA as monomers. The flame retardant group was introduced into the structure of PA polymer chain, without sacrificing the mechanical properties of PA, the flame retardant effect was obvious and the flame retardant persistence was high. The reactive flame retardant contains a number of benzene rings and N-P structures. Benzene ring can increase the internal spin resistance of the main chain of PA and improve the thermal stability of the material. N-P structure fracture can produce nitrogen-containing phosphate compounds, nitrogen-containing compounds decompose to produce NH3 and H _ 2O, promote PA foaming, phosphoric acid compounds are heated to form polymetaphosphoric acid, promote the formation of carbon, the formation of char has the effect of flame retardant to PA.

 

5. Addition of synergistic flame retardant

There are a series of problems in the use of flame retardants alone, such as poor compatibility between phosphorous flame retardants/nitrogen flame retardants and matrix, and difficulty in distribution; phosphorous flame retardants (AHP) are prone to fire caused by phosphine. The process of reactive flame retardant is complex and the cost is high. The content of inorganic flame retardant is large, the mechanical properties of the material are reduced, and the carbon layer is discontinuous after combustion. In order to reduce the probability of the above problems, various kinds of flame retardants can be used in flame retardant PA.. After blending, the cost and pollution of flame retardant are reduced, and the flame retardant efficiency is improved. The common compound systems are phosphorous flame retardants and inorganic materials.

 

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