Classification and development of flame retardant nylon materials

PA is a self extinguishing polymer with a vertical combustion rating of UL 94 V in accordance with ASTM standards_ Grade 2, the oxygen index is about 24%, which has a certain fire resistance. With the wide application of PA in the field of transportation, electronic and electrical equipment, construction and other special industries, its application environment is becoming more and more harsh, such as high temperature, high humidity and high voltage. Moreover, with the comfort and convenience of PA, its flammability also brings potential fire hazards

In the world, more and more attention has been paid to the research, development, production and application of flame retardant PA modification, which has become a common concern and research topic in academia and industry.

Flame retardant way of PA

(1) Using additive flame retardant, i.e. adding flame retardant to pa by mechanical mixing method, to enhance the flame retardancy of materials, this method is convenient to use and widely applicable.

(2) The use of reactive flame retardant, that is, the flame retardant as a reaction monomer to participate in the reaction, and combined with the main chain or side chain of PA, so that PA itself contains flame retardant components. It is characterized by low toxicity, good stability and long flame retardancy. But processing

The process is complex and the cost is high. So it is common to adopt the first way of flame retardant.

Problems of PA flame retardant modification

1 moisture in raw materials

Because of the strong polar amide group in PA molecular structure, it is easy to combine with water molecules to form hydrogen bond when exposed to air, which makes PA prone to hydrolysis reaction and greatly reduces its mechanical properties. Therefore, in Canada

The raw materials must be fully dried before use.

2 processing temperature

The processing temperature shall follow the following principles: the temperature of the feeding section is slightly lower than the melting point of the raw material, making PA semi molten; the temperature of the compression section is generally about 10-15 ℃ higher than the melting point, making it fully molten; the temperature of the metering section is close to or slightly lower than the compression section

Temperature, the PA melt in this area is evenly heated, easy to achieve stable flow; the head temperature is slightly lower than the temperature of the metering section, basically close to the melting point, so as to avoid the uneven thickness of the product caused by the melt fracture. In addition, the temperature and cooling speed of the cooling medium should also be

Make appropriate adjustments.

Types and application of 3 Pa flame retardant

At present, there are many kinds of flame retardants that can be used for PA, such as halogen flame retardants such as decabromodiphenylethane, brominated polystyrene, phosphorus flame retardants such as red phosphorus, nitrogen flame retardants such as melamine salt, solid flame retardants such as antimony trioxide, zinc borate and a few mineral flame retardants.

1 halogen flame retardant

Up to now, most of PA flame retardant products are based on halogenated compounds. Halogenated flame retardants are the most widely used chemical flame retardants in the world, which have good flame retardancy and influence on the mechanical properties of materials

The noise is small.

It should be noted that the halogenated flame retardants will produce thick smoke in the combustion process, release toxic hydrogen halide gas and toxic substance dioxin (DPO), which will seriously stimulate human eyes and respiratory system, and at the same time, bring to production application and external environment

It is a serious "secondary disaster". On February 13, 2003, the European Union issued the directive on banning the use of certain harmful substances in electronic and electrical equipment, which strictly stipulated that polybrominated diphenyl ether should not be used in electronic and electrical equipment

Halogen flame retardants have been restricted in the world. Therefore, with the gradual improvement of people's awareness of environmental protection, practical and efficient environmental friendly low halogen or halogen-free flame retardants have attracted more and more attention.

2 phosphorus flame retardant

High efficiency, low toxicity, halogen-free and environmental protection are the trend of flame retardant development. With the development of flame retardant research, PA Flame Retardants Containing Nitrogen and phosphorus are increasingly favored by nylon modified manufacturers.

Phosphorus flame retardants include inorganic phosphorus and organic phosphorus, among which inorganic phosphorus refers to red phosphorus and some phosphates. The flame retardant mechanism of phosphorous flame retardant is basically the same, which mainly plays the role of flame retardant between solid phase and liquid phase, i.e. formed by decomposition

The high boiling point oxygenic acid can dehydrate and carbonize the polymer, which can insulate the air and change the combustion mode of the polymer.

The pyrolyzed product Po. Free radical can capture ho. Free radical after entering the gas phase, and it also has a certain gas-phase flame-retardant effect.

However, red phosphorus is easy to absorb moisture when exposed to the air, and chemical reactions will occur, forming phosphoric acid, hypophosphite and even toxic phosphine gas, which also has limitations in its storage and color, all of which limit its application in light color PA products.

3 nitrogen flame retardant

Nitrogen flame retardants belong to melamine salts, mainly dicyandiamide and melamine ureate (MCA). The flame-retardant mechanism is gas-phase flame-retardant, which produces non combustible gases such as CO, ammonia (NH) in the decomposition process, and plays a role of flame-retardant by diluting the combustible gas concentration to block the air. Nitrogen series flame retardant has the advantages of low smoke, non-toxic or low toxicity, low corrosiveness and so on. It is stable to heat and ultraviolet light, which greatly caters to the development trend of flame retardant in the direction of high efficiency and low toxicity. It has been widely studied and applied at home and abroad.

However, MCA is mainly gas-phase flame-retardant, the amount of carbon in the condensed phase is low, and the carbon layer is loose, so it can not form a dense protective layer, which limits its flame-retardant effect. Because of its poor thermal stability and easy moisture absorption, the electrical properties of the products are decreased in the humid environment, so it can only be used in the occasions with low flame retardant requirements. In addition, the application of this kind of flame retardant in reinforced flame retardant nylon will make the material produce wick effect, and the flame retardant effect will be greatly reduced

4 intumescent flame retardant

In recent years, the research of intumescent flame retardant (IFR) has been paid more and more attention. IFR has the characteristics of low smoke, non-toxic, high flame-retardant efficiency, no molten drop, no corrosive gas release and so on. It is considered to be the current halogen-free flame-retardant materials

One of the development directions. IFR is usually composed of gas source, acid source and carbon source. During combustion, foaming and carbonization are carried out simultaneously to form porous expansion carbon layer. This carbon layer has the functions of heat insulation, oxygen isolation, smoke suppression and droplet prevention, with excellent flame retardant performance. Some new

The intumescent flame retardant is composed of nitrogen and phosphorus flame retardant system, in which nitrogen-containing flame retardant is an excellent gas source (for foaming), while phosphorus-containing flame retardant is an excellent acid source (for dehydration). However, the application of this kind of flame retardant in nylon still needs to solve the problems of flame retardancy and high temperature resistance

5 inorganic filler type flame retardant

Inorganic filler type flame retardant is mostly powder, which belongs to additive type flame retardant. It has rich sources, non-volatile, non-toxic, smoke suppression, and has a wide range of applications at home and abroad. Among the inorganic fillers for PA, Al (OH) and Mg (OH) are used

The main mechanism of flame-retardant is to absorb heat when it is burned and decomposed. The water vapor produced can dilute the air, and the remaining residue can prevent the transfer of heat and substance. The main disadvantages are high surface polarity, poor compatibility with resin

It is easy to cause the degradation of the mechanical properties of the material with a large amount of additives (the mass fraction is generally more than 60%).

6 nanometer layered silicate

In recent years, there has been a new way to use intercalation technology to flame retardant polymer, and the research on polymer / layered silicate nanocomposites is developing rapidly. Among the layered silicates which can be intercalated, montmorillonite is the most easy intercalation because of the oxygen atoms between the unit layers. By means of melting intercalation, PA6 molecules can be inserted into the organic montmorillonite layer. PA6 / montmorillonite intercalation composite is successfully prepared. 5% montmorillonite can help to form carbon when burning. The carbon layer can play the role of heat insulation and blocking the passage of volatile substances, which makes the material have low heat release rate and mass loss, greatly improving the flame retardant performance. In addition, montmorillonite intercalation material and other flame retardants are used together, which also has a good synergistic effect on PA flame retardants.

With the development of flame retardant technology, flame retardant PA has the following development trends: (1) no halogenation, low toxicity. In the future, the demand for halogen-free flame retardants and environmentally friendly flame retardants will increase greatly; (2) the research on synergistic flame retardant system. Using one flame retardant alone usually can't meet the high demand of flame retardant, and many flame retardant composite systems often have excellent synergistic effect. Therefore, how to develop a new flame retardant with excellent performance through composite technology is an important research topic; (3) multifunctional. At present, most of the flame-retardant PA systems only emphasize the flame-retardant properties, but more or less sacrifice some other excellent properties. The development of multi-functional flame retardants has great potential and is the trend of the situation. It can not only improve the flame retardancy of materials, but also enhance the impact resistance, flame retardancy, conductivity, anti-static and other properties.