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PBB and PBDE as flame retardants are often found in PP, PA, PE, PS, ABS, EVA, PET, PBT and other flammable plastics products.PBB, PBDE in the uncontrolled combustion process (temperatures lower than 1200 degrees) may produce brominated dibenzo-p-dioxins/furans (PBDD/F), which are strongly carcinogenic and teratogenic substances. These substances may cause serious and wide-ranging ecological pollution of air, rivers and water bodies. Therefore, EU RoHS and other relevant directives prohibit the use of polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) in plastic products. Flame retardants are generally divided into organic flame retardants (such as halogenated flame retardants PBB, phosphate esters) and inorganic flame retardants (such as aluminum hydroxide, zinc borate). Apart from the restricted PBB and PBDE, the most common flame retardants currently used in industry are phosphate esters, antimony oxide, aluminum hydroxide and zinc borate. The following is a brief overview of the different flame retardant alternatives. 1. Aluminum hydroxide (magnesium) Aluminum hydroxide is an inorganic flame retardant, and its flame retardant mechanism is heat decomposition to release a large amount of water vapor, the reaction formula: 2Al(OH)3 → A1203 + 3H2O This is a strong heat absorption reaction, heat absorption reaches l967.2J/g, play the role of the cooling of the polymer, the reaction of the resulting water vapor can be Dilute combustible gases, inhibit the spread of combustion, the new generation of aluminum oxide also has a high activity, can adsorb soot particles, play a role in suppressing smoke. In addition, aluminum hydroxide also has a drip, promote carbonization, can be retained in the polymer for a long time and can increase its resistance to arc.Al(OH)3 has the advantages of high stability, non-volatile, low cost, etc., therefore, it is known as "pollution-free flame retardant". However, some of its shortcomings also restrict its application. Because it is a polar inorganic material, Al(OH)3 has poor affinity with organic polymers and small interfacial bonding force, so it is filled with large amount of poor compatibility, which is not conducive to the processing of polymers and reduces the mechanical properties of the products. In order to overcome these shortcomings, coupling agents are commonly used for surface treatment. Commonly used coupling agents are silane and phthalate vinegar. The surface treatment can improve the affinity of Al(OH)3 to the matrix to ensure the original impact strength of the material. In addition, improving the granulation technology to narrow the particle size distribution and obtain ultra-fine particle size Al(OH)3, which can make Al(OH)3 more uniformly dispersed in the synthetic material, improve the mechanical properties and heat resistance of the matrix material, and improve the flame retardant effect. With the continuous improvement of the particle size distribution of Al(OH)3 and the application of surface treatment technology, its mass fraction rises from 40% to 60%, and the physical properties of the products are continuously enhanced. Aluminum hydroxide flame retardant is mainly used in plastics, rubber, SMC\BMC, artificial marble and insulation and electrical fillers and other industries. The common domestic suppliers of aluminum hydroxide flame retardant are Hefei Zhongke Flame Retardant New Material Co. Ltd. and Suzhou Nafang Engineering Materials Co., Ltd. etc. Similar to aluminum hydroxide flame retardant principle and performance, there is magnesium hydroxide flame retardant (Mg(OH)2), and its common domestic suppliers are Zhengzhou Fulong New Material Science and Technology Co. In the presence of water vapor is oxidized into viscous phosphorus oxygenated acid, this kind of acid that covers the surface of the flame retardant material, prompting the material surface to accelerate the dehydration of carbonization, the formation of carbon layer. Liquid film and carbon layer can play the role of heat storage, prevent gas exchange, to protect the lower layer will not continue to be oxidized, and play a role in flame retardant. However, in practical application, red phosphorus is easy to absorb moisture, oxidation, and release highly toxic gases, dust is easy to explode, and it is dark red, there is a danger of fire in the process of mixing with resin, molding, and other processing operations, and poor compatibility with the resin, it is not suitable for dispersion of uniformity, which results in the decline in the physical properties of the substrate. In order to overcome these shortcomings, the surface modification treatment of red phosphorus particles has become one of the important research topics. At present, the commonly adopted method is microencapsulation: Al(OH)3, metal sulfate, synthetic resin, etc. are used to coat the surface of red phosphorus to form a layer of "thin wall" to improve the interfacial bonding ability and overcome the shortcomings of red phosphorus as a flame retardant. Microencapsulated red phosphorus (MRP) is a common product on the market today. MRPs are mainly used in the flame retardancy of engineering plastics such as polyethylene, polypropylene, ABS, high impact polystyrene, nylon, epoxy resin and so on. The common suppliers of red phosphorus flame retardant in China are Xiangshuo Plastic Flame Retardant Material Co., Ltd. and Maanshan Yuanchuan Flame Retardant Material Co. 3. Zinc Boric Acid Zinc boric acid is a white or light yellow crystalline powder, which is a multifunctional inorganic additive flame retardant with a molecule of 2ZnO-3B2O3-3.5H2O. It has a solubility of 0.28%wt. in water at room temperature and is insoluble in cold water and slightly soluble in hot water. Slightly soluble in cold water, slightly soluble in hot water, hydrolyzed by strong acid or alkali, soluble in hydrochloric acid, sulfuric acid, dimethyl sulfoxide, soluble in ammonia, slightly less soluble in sodium hydroxide, insoluble in ethanol, n-butanol, benzene and acetone and other organic solvents. Zinc borate has good thermal stability, high water loss temperature, the temperature of water of crystallization can reach more than 300℃. Small relative density, fine particle size, easy dispersion and non-toxicity are its unique features. The flame retardant mechanism of zinc borate is to exert its flame retardant effect through several pathways or mechanisms such as heat absorption, covering effect, inhibition of chain reaction and release of non-flammable gas. Compared with other organic and inorganic flame retardants. Its flame retardant effect is better, good smoke suppression (can reduce the amount of black smoke burning 25%), can maintain the transparency of transparent plastics, the use of the advantages of no treatment. Zinc borate has a variety of excellent properties, of which the synergistic effect is particularly significant, which makes its application more widely. Among inorganic flame retardants, aluminum hydroxide has three functions: flame retardant, smoke reduction and filling. Because it is non-volatile, non-toxic, and can produce synergistic flame retardant effects with a variety of substances, it is known as a harmless inorganic flame retardant. However, aluminum hydroxide usually needs to be added more than 50% (mass fraction) to show a good flame retardant effect. The same is true for magnesium hydroxide and aluminum hydroxide. This will be due to a large number of additions to make the base material resin processing performance deterioration. The loss of mechanical properties is large. Antimony trioxide is an essential synergist for halogen flame retardants, but the flame retardant effect is very small when used alone. Zinc borate due to a high dehydration temperature (greater than 300 ℃), more than most of the polymer decomposition temperature, can be used in whole or in part instead of antimony trioxide thermosetting polyester formulations, reducing the use of cost, but also with aluminum hydroxide, magnesium hydroxide and phosphorus flame retardant to produce a good synergistic effect, thereby reducing the amount of their additions, reduce their impact on the processing performance of the substrate. Zinc borate is mainly used in the processing of plastics and rubber, such as PVC, PE, PP, reinforced polyamide, polychlorinated resin, polystyrene, epoxy resins, polyethylene terephthalate resins and natural rubber, styrene butadiene rubber, neoprene rubber and so on. It can also be used in the production of paper, fiber fabrics, decorative panels, floor leather, wallpaper, carpets, ceramic glazes, fungicides, and coatings to improve flame retardant properties. The common domestic suppliers of zinc borate for Zibo five-dimensional Industrial Company Limited, Henan Province, Tianlong Flame Retardant Materials Company Limited, etc. 4. Ammonium polyphosphate Ammonium polyphosphate is a good inorganic flame retardant, white powder, decomposition temperature is greater than 256 ℃, the degree of polymerization of 10-20 water-soluble, degree of polymerization of more than 20 difficult to dissolve in water. It is cheaper than organic flame retardant, with low toxicity and good thermal stability, and can be used as flame retardant for plastics either alone or in combination with other flame retardants. Under high temperature, it is rapidly decomposed into ammonia and polyphosphoric acid, and ammonia can dilute the oxygen concentration in the gas phase, thus preventing the role of combustion. Polyphosphoric acid is a strong dehydrating agent, which can make the polymer dehydrate and carbonize to form a carbon layer, isolate the polymer and oxygen contact, and prevent combustion. Ammonium polyphosphate is mainly used in intumescent fireproof coating, polyethylene, polypropylene, polyurethane, epoxy resin, rubber products, fiberboard and dry powder fire extinguishing agent. The common domestic suppliers of ammonium polyphosphate are Jinan Jinyingtai Chemical Co., Ltd, Fuyuan Chemical Co., Ltd, Shanghai Xinhua Flame Retardant General Factory, etc. 5. Phosphate ester (organophosphorus) phosphate ester organophosphorus flame retardant has good compatibility with the base material and has the double effect of flame retardant and plasticizer, which is the most widely used in organophosphorus flame retardant. However, organophosphorus flame retardants are mostly liquids with the disadvantages of high volatility, high mobility, high smoke generation and poor thermal stability, which limit their application. In order to overcome these shortcomings, the use of polycondensation reaction to produce a high relative molecular mass of organophosphorus flame retardants, can effectively reduce its volatility. Phosphate flame retardants are mainly used in PC, PC/ABS, PPO/HIPS and other polymers. The common domestic suppliers are Shenzhen Jirui Chemical Co., Ltd, Hebei Zhenxing Chemical & Rubber Co. 6. Melamine (Organic Nitrogen-based) Commonly used organic nitrogen-based flame retardants are melamine and its derivatives. Nitrogen flame retardants have low toxicity, high flame retardant efficiency and good heat resistance. Due to the high thermal decomposition temperature, there is no need to worry about flame retardant failure due to decomposition of the flame retardant during processing of the material. In addition, when nitrogen-containing compounds decompose, the gas generated is less corrosive, and the polymer materials treated with nitrogen-based flame retardants have low smoke emission and show good smoke suppression effects. However, when melamine is used alone, the flame retardant efficiency is not high, so it needs to be compounded with other flame retardants to produce a synergistic effect, in order to improve the flame retardant efficiency. Usually melamine is used in combination with polyphosphoric acid amine and pentaerythritol. Melamine organic nitrogen flame retardant is mainly used in the manufacture of intumescent fire retardant coatings in the foaming component, its foaming effect is good, dense carbon. In addition to being used as flame retardant alone, the commonly used flame retardant varieties are the derivative salts produced by reacting with acid, which are widely used in the fields of thermoplastic and thermosetting plastics such as PE, PP and PVC plastics, etc. Melamine is used in combination with liquid phosphate, which is widely used in flame retardant polyurethane foam materials. The common suppliers of melamine in China are Shanghai Haiyi Industry and Trade Co., Ltd. and Lianyungang Legend Flame Retardant Material Co. 7. Expansion flame retardants can be divided into filler flame retardants and expansion flame retardants. Inorganic flame retardants are mostly filler flame retardants, which have the advantages of less smoke emission and no harmful gas during combustion. However, their own flame retardant efficiency is not high, filled with a large number of flame retardants to achieve a certain effect. Therefore, it is necessary to modify the flame retardant or add flame retardant synergist to achieve better flame retardant effect. Common processing technologies are: ultrafine and nano technology, surface treatment and coating technology, microencapsulation of red phosphorus as flame retardant synergist. As for the expansion type flame retardant, it is mostly composed of a variety of flame retardants, and has three main components, namely, carbon forming agent (carbon source), dehydrating agent (acid source) and foaming agent (gas source). Among them, the charcoal-forming agent refers to the substance that can be charred by the dehydrating agent by taking away the water in the combustion process. It is mainly some polyhydroxy organic compounds with high carbon content. The common ones are pentaerythritol, in addition, nylon 6 has high charring efficiency and is more widely used. Dehydrating agent refers to the substance that takes the moisture of the charring agent in the combustion process of expansion flame retardant, and its main function is to promote the dehydration and carbonization of multi-hydroxy compounds, and form the charcoal layer with a certain thickness which is not easy to be burned. Dehydrating agent is mainly some inorganic acid salts and inorganic acid esters. The most used are ammonium phosphate, phosphate esters, borates and silicates. Foaming agent, when heated in the flame retardant system, the decomposition releases a large number of non-toxic and can extinguish the gas, while expansion occurs and the formation of spongy fine bubble structure of the compound. Commonly used foaming agents include melamine, dicyandiamide, ammonium polyphosphate, amine borate, dicyandiamide formaldehyde resin and so on. After the synergistic effect of the above flame retardants, the intumescent flame retardants can decompose the non-combustible gases generated to make the molten state of the system foaming and expansion, and the inorganic acid begins to dewater the polyol and ester carbonization, the formation of charcoal residue and inorganic substances, and ultimately make the system open gelatinization and curing, the formation of a foam carbon layer with microcellular structure with heat insulation and oxygen insulation. Intumescent flame retardants are mainly used in the flame retardant of PE, PP and other plastics. The common domestic suppliers are Weihai Tianchuang Chemical Co. When flame retardant materials are used for fire protection in humid environments, marine climates, open-air environments, etc., the application of traditional intumescent flame retardants is somewhat limited due to their weather resistance, salinity and water solubility. Expandable graphite (EG) is a new type of intumescent flame retardant developed recently. It can well overcome the shortcomings of traditional intumescent flame retardants and has a wider scope of application. Natural graphite is specially treated to form a special interlayer compound. When rapidly heated to over 300℃, it can expand hundreds of times along one axis. The expanded graphite forms a thick porous carbon layer, which plays the role of heat insulation.EG is rich in resources, simple to manufacture, inexpensive, non-toxic and low smoke. In practical use, it needs to be compounded with other substances (such as red phosphorus) to produce synergistic effect. The common suppliers of expanded graphite flame retardant in China are Qingdao Baichuan Graphite Co. Environmentally friendly flame retardants also include silicone flame retardants (such as silicone oil, silicone resin, silicone rubber, silane coupling agent, etc.) and new nanomaterials flame retardant, due to the development of the late, the application is not very extensive. In addition, there are PBB and PBDE-free bromine flame retardants, such as decabromodiphenyl ethane, decabromodiphenyl ether, etc. Although they can meet the requirements of RoHS, etc., they have been questioned because they contain halogens, and are expected to be restricted in the near future.