Flame retardants are a kind of additives which can improve the flame retardancy, self-extinguishing and smoke suppression of flammable or combustible materials. In general, flame retardants can be divided into organic and inorganic types. In the plastic industry, inorganic flame retardants have the advantages of good thermal stability, non-volatile, non-precipitation, non-corrosive toxic gases, etc. , there has been rapid development in recent years. Among inorganic flame retardants, Magnesium hydroxide has many functions, such as flame retardancy, smoke suppression, anti-dripping, filling and so on.
The classification of Magnesium hydroxide
The Magnesium hydroxide can be divided into two mode of production, mechanical grinding (also known as brucite) and chemical synthesis, of which mechanical grinding has a production capacity of 300,000-500,000 tonnes, mainly concentrated in Liaoning province. Chemical synthesis can be divided into hydrothermal method, precipitation method, magnesium oxide hydration method. Magnesium hydroxide flame retardants are used in a variety of rubber and plastics, with the largest use being in ultra-fine Magnesium hydroxide prepared by mechanical grinding.
Ultra-fine Magnesium hydroxide is a kind of inorganic flame retardant made from natural brucite mineral by ultra-fine grinding and certain surface treatment. The Magnesium hydroxide flame retardant produced from brucite is made from natural minerals at source. The whole process of processing is basically emission-free. It can be said that both the source and the product meet the requirements of greening and are non-toxic and harmless, as an environment-friendly flame retardant, so known as“Green environment-friendly flame retardant”, has a huge market application prospects.
Brief introduction of brucite
Brucite is a Magnesium hydroxide mineral with high content of magnesium in nature. Its theoretical composition is 69.12% MGO and 30.88% H2O. Brucite is a kind of trigonal crystal system. It is usually lamellar aggregate and sometimes fibrous aggregate. Its cleavage surface is pearl luster, hardness is 2.5, specific gravity is 2.3 ~ 2.6 g/cm3.
China is a large magnesium resource country, and Magnesium hydroxide flame retardants have unique resource advantages and good market prospects. According to statistics, the national reserves of brucite is about 25 million tons, of which: Liaoning province, Qingyuan, Kuandian Manchu Autonomous County brucite reserves of 10 million tons, is the world’s largest discovered brucite ore; In addition, brucite deposits have been found in Xixia, Qilian Mountains and Jianshibao in Sichuan Province.
The Magnesium hydroxide mechanism of flame retardants
Inorganic flame retardants are generally in the gas phase or condensed phase play a flame retardant role. For Magnesium hydroxide flame retardants, the mechanism can be summarized as follows:
Cooling effect the Magnesium hydroxide decomposes when heated and absorbs a large amount of latent heat, thereby reducing the actual temperature of the polymer surface, slowing down the rate of polymer cracking and reducing the generation of combustibles;
2) dilution effect. A large amount of water vapor is released from the Magnesium hydroxide when it is heated and burned. Water vapor is a non-flammable gas. It can dilute the flammable gas and the oxygen on the surface, so that the combustion can not continue. At the same time, the amount of Magnesium hydroxide flame retardants filled in the polymer system is large, which can also dilute the concentration of combustibles in the solid phase to some extent, thus improving the flame retardancy of the products
3) isolation effect. When the Magnesium hydroxide is heated, it decomposes to form a dense layer of magnesium oxide, an excellent Refractory that coats the polymer, increasing its flame resistance and preventing combustion by insulating it from the air. The decomposed mgo is also beneficial to the formation of carbon on the polymer surface, and the carbon layer is also an excellent insulating layer
4) smoking inhibition effect. The flame retardancy of the Magnesium hydroxide occurs mainly in the outer layers of the solid degradation zone and has little effect on the solid degradation zone and the pre-combustion zone. The smoke released by the combustion of the outer layer of the Magnesium hydroxide is diluted or absorbed by the water vapor generated during the decomposition process, thus having a better smoke suppression effect.
In conclusion, Magnesium hydroxide is a kind of additive flame retardants with multiple functions such as flame retardancy, smoke suppression, anti-dripping and filling. It can not only neutralize the acidic corrosive gases produced in the combustion process, but also has many advantages, also does not emit harmful substances, is a green environment-friendly flame retardant.
The advantages of Magnesium hydroxide flame retardants
Due to its good thermal stability, the Magnesium hydroxide is non-corrosive, non-volatile, long-lasting, non-toxic and inexpensive. Compared with Aluminum hydroxide, it has higher thermal decomposition temperature and obvious advantages in flame retardant mechanism, decomposition ability, heat capacity, carbonization, smoke suppression ability, hardness, production cost, etc. . Specifically:
A) the decomposition energy of Magnesium hydroxide (1137kjg) is higher than that of Aluminum hydroxide (1117kjg) , and the heat capacity is 7% higher, which helps to improve the flame retardant efficiency;
B) the hardness of the Magnesium hydroxide is lower than that of the Aluminum hydroxide, and the wear and tear of the equipment is less during processing, thus prolonging the service life of the equipment;
C) the thermal stability of the Magnesium hydroxide is better than that of the Aluminum hydroxide. The Magnesium hydroxide decompose at a higher temperature of about 340 â ° C, while the Aluminum hydroxide decompose at 220 â ° C, so that the Magnesium hydroxide can withstand higher processing temperatures, which is conducive to faster extrusion, especially for polymers with higher processing temperatures.
D) Magnesium hydroxide is an additive flame retardant, which has better smoke suppression effect than Aluminum hydroxide inorganic flame retardants;
E) experimental studies have shown that Magnesium hydroxide are better than Aluminum hydroxide in promoting carbon formation on polymer surfaces, and therefore better than Aluminum hydroxide in flame retardancy.
With the increasing of environmental protection, the development of flame retardants in the world shows the trend of non-halogenation and low smoke, which makes the consumption of inorganic flame retardants, the main Magnesium hydroxide, increase rapidly.
Application of Magnesium hydroxide flame retardants
As a kind of green flame retardant, Magnesium hydroxide is widely used in polyvinyl chloride, polyethylene, EPDM rubber and unsaturated polyester, it is a low smoke halogen-free flame retardant, smoke suppressant and filler for Conveyer Belt, ventilation pipe, wire and cable sheath, flame-retardant aluminum-plastic board, flame-retardant plastic floor and fire-retardant coating.
1) wire and cable (PVC)
Our country is a big country of PVC cable, in which flame-retardant cable accounts for about 60% of cable products. PVC breaks down when it burns and is emitted with toxic hydrogen chloride and other acidic gases, which can cause significant loss of life. Magnesium hydroxide flame retardants are used to fill polyvinyl chloride and can absorb toxic gases. After adding Magnesium hydroxide, the oxygen index of the product system increased, while the burning rate and smoke emission decreased obviously, which endowed the products with excellent functions such as flame retardant, smoke suppression and high temperature resistance. In addition, the mechanical properties, processability and electrical properties of the composite can be improved.
2) pipe & Profile (pp)
Because of the flammability of polypropylene polymers, high-efficiency flame retardants are usually added to the formulation of flame-retardant grade polypropylene. At the same time, the processing temperature of polypropylene is usually over 200 â ° C, and the Magnesium hydroxide flame retardants are completely comparable, is the best choice for processing this kind of products. By choosing suitable Magnesium hydroxide flame retardants, not only the bending strength and bending modulus of the products can be improved, the heat resistance of the products can be improved, but also the requirements of flame retardancy can be met.
3) polyolefin compound (HFFR)
Polyolefin compounds are gradually replacing PVC-based compounds and are widely used in areas with strict requirements for smoke and toxic gas emissions, especially in underground pipelines, public places, areas such as insulated wire and cable. These materials are processed at high temperatures up to 300 ° C. As a result, many polyolefin producers produce dense final products based on Magnesium hydroxide flame retardants. The Magnesium hydroxide can improve the processability, excellent mechanical properties and high thermal stability of the products.
4) crosslinked polyethylene (XLPE)
Crosslinked polyethylene (XLPE) is considered a good material in many fields of insulation and piping. The high temperature of the process makes Magnesium hydroxide the preferred flame retardant, furthermore, the Magnesium hydroxide can improve the thermal stability of the product and enhance the surface gloss and brightness.
5) rubber
Rubber products, including conveyor belts used in the mining industry and hoses in public utilities. Pure rubber is a highly flammable substance, so all rubber products must be formulated with flame retardants. Some neoprene may release large amounts of hydrogen chloride gas during combustion, which makes fire more dangerous. The Magnesium hydroxide adsorbs toxic gases and has a good smoke suppression effect, giving it excellent flame retardancy.
6) silica gel
Silica gel is used in sealing, gasket, electronic and electrical cable and other products. But the highly flammable nature of silicone requires the addition of flame retardants, and Magnesium hydroxide is the most suitable product for this purpose.
7) floor & Wallboard
The most common wall panels and flooring on the market today are based on either polyvinyl chloride or polyethylene. To create a safe home environment, flame retardants are commonly added to PVC-based floor materials. Magnesium hydroxide flame retardants are effective in reducing smoke and absorbing acidic gases. The vertical characteristics of the wallboard, it is easy to form a vertical combustion, coupled with the matrix is a polyethylene polymer, the need to use Magnesium hydroxide flame retardant flame retardant. The Magnesium hydroxide can improve the gloss and hardness of the products, and improve the heat resistance and flame retardancy of the products.
8) fire retardant coatings
The temperature of thermal decomposition and dehydration of Magnesium hydroxide is between 420 ° C and 520 ° C, which is close to the combustion temperature of organic matter, so it can be used as a flame retardant for fire retardant coatings. When added to a fire retardant coating, the Magnesium hydroxide will not break down into gaseous compounds and be lost when exposed to fire or even in a continuous flame. It is highly stable and can play a role in long-lasting flame resistance, therefore, the fireproof coating has the high efficiency heat insulation fireproof performance.
9) copper clad laminate
The application of Magnesium hydroxide in copper clad laminate can meet the requirements of high heat resistance of products, endow products with excellent electrical insulation performance and make them more compatible with resins, it has obvious effect on improving the surface and mechanical properties of copper clad laminate. It has the advantages of high flame-retardant efficiency, strong smoke suppression ability, low hardness and low friction to the equipment, which is helpful to prolong the life of the equipment.
Electrical components (polyamide)
Most insulators, switches, plugs and sockets must meet the most stringent fire protection standards. In the formulation of Polyamide products, the addition of Magnesium hydroxide improves the processing fluidity, appearance, electrical and physical properties, and thermal stability of the products.
11) other applications
Magnesium hydroxide is commonly used in adhesives as an additive flame retardant or as a flame retardant filler, and can be used in the manufacture of magnesium salt, active magnesium oxide, fine ceramics, thermal insulation materials, sugar refining, flue gas desulphurization agent, oil anti-corrosion additives, wastewater neutralization agent.