Progress in halogen-free flame retardant technolog

2022-08-09
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Progress in halogen-free flame retardant technology of plastics

plastics are widely used in industry, agriculture and daily life, but almost all plastics are easy to burn, and some of them will produce a large number of harmful gases and smoke when burning. The potential fire hazards caused by this have become a global concern. At present, adding effective flame retardants is a common method in flame retardant technology

halogen flame retardants have good cost-effectiveness balance and wide adaptability, and still occupy the leading position in plastic flame retardant formula. However, halogen flame retardants have a large amount of smoke, and the hydrogen halide gas released is highly corrosive, which hides secondary hazards. It is reported that polybrominated benzofuran (pbdf) will be produced when plastic flame retardant with polybrominated diphenyl ether is burned. This substance has strong carcinogenic effect, which is called "dioxin is Sue" in western countries, so its use is limited. The environmental protection organizations of the European Community countries have clearly issued a decree banning the entry of plastics containing halogen flame retardants into the European market. Based on the understanding of environmental protection, the flame retardation of plastics has tended to be halogen-free

at present, inorganic flame retardants account for 50% in Europe, 60% in the United States and 64% in Japan. It can be seen that inorganic flame retardants are the most used in all countries, while China's development in this area is insufficient, accounting for only 17%. In recent years, the development of inorganic flame retardants in China has attracted extensive attention and is developing rapidly

according to the typical varieties of halogen-free flame retardants, they are divided into inorganic metal compounds, phosphorus series, nitrogen series and silicon series

1. inorganic metal compounds

the most representative of this class are hydrated metal compounds, such as Al (OH) 3 and Mg (OH) 2, which account for the majority of halogen-free flame retardants. As flame retardants, they are characterized by a large number of coordination to meet the requirements of UL94V0 flame retardance, but they increase the viscosity of the components, reduce the molding processability, water resistance and mechanical properties, and do not produce toxic gases when burning, and have both flame retardancy and low smoke effect

the dehydration and endothermic temperature of aluminum hydroxide is ℃, and the endothermic capacity is 1968j, but what deserves the attention of enterprises are: 1. The growth rate of automobile production and sales volume with the largest weight in the total industrial volume is picking up; 2. The cumulative order amount of key enterprises in the machinery industry has warmed up/g, which can inhibit the rise of material temperature in the early stage. At present, the flame retardancy is mainly improved through the following ways

① surface activation uses coupling agents to improve the processability, water resistance and electrical properties of aluminum hydroxide. For example, lubral with surface treatment of Alcoa company in the United States; H-34, h-34hl and h-312 of Showa light metal company in Japan

② ultrafine particle diameter, particle size distribution and particle shape can improve its dehydration temperature and processability. For example, Salem industries of the United States mechanically grinds ultra-fine Micra 1910 and mi-cra932, with an average particle size of only 0.6 ц m. The particle size of superfine varieties in Shandong Aluminum plant can be as small as 0.5 ц m。

③ compound aluminum hydroxide combined with some inorganic compounds can improve flame retardancy and smoke suppression, such as ammonium molybdate, zinc oxide, antimony oxide, red phosphorus, etc

④ enhance fibrosis. The sodalite [naal (OH) 2co3] flame retardant developed by Alcoa company in the United States has both flame retardant and reinforcing effects for plastics. The special crystalline mg Al basic salt developed by Jiangsu Institute of comprehensive utilization of seawater can not only endow plastics with flame retardancy, but also have fiber filling effect

because aluminum hydroxide is environmentally friendly and cheap, its consumption has maintained a high growth rate, and its proportion in the total consumption of flame retardants has increased from about 30% in to nearly 50% in 1984. Until now, this proportion has remained stable

magnesium hydroxide decomposes at ℃, and the endothermic capacity is 783j/g. it needs a higher temperature to start the dehydration reaction, and the endothermic capacity is small. It is worse than aluminum hydroxide in inhibiting the temperature rise of the material, but its carbonization effect on the polymer is better than aluminum hydroxide. Magnesium hydroxide also needs surface activation to improve the interface characteristics with the matrix resin. In foreign countries, modified magnesium hydroxide has been widely used in PP, PE, PS, PVC, ABS, PA and other engineering plastics, rubber and elastomers

using the mixture of magnesium hydroxide and aluminum hydroxide as flame retardant can have their own advantages. In recent years, the research on flame retardant synergistic effect of inorganic hydroxide is also very popular. The common synergists in Al (OH) 3/Mg (OH) 2 flame retardant system are red phosphorus, phosphate ester, ammonium polyphosphate, silicone and so on

other inorganic metal compound flame retardants include zinc borate, aluminum compound, tin compound, zirconia, copper oxide, cuprous oxide and other metal compounds. In recent years, the development of composite flame retardants and their synergy are valuable development directions

with the rise of nano materials, polymer/nano materials may become a new generation of flame retardant polymer materials. At present, nylon 6/layered silicate (pa6/ls) is in the development stage as a new flame retardant material

2. Phosphorus flame retardants also play an important role in halogen-free flame retardants. According to the composition and structure, it can be divided into inorganic and organic phosphorus flame retardants. The former is mainly red phosphorus and phosphate, and the latter is mainly phosphate, phosphite and phosphonate

inorganic phosphorus flame retardants such as red phosphorus, ammonium phosphate and ammonium polyphosphate have been used earlier, and many industrialized products have been launched abroad. Red phosphorus is used more and more in Europe, mainly in polyamide, epoxy resin, polyolefin and polyurethane, and is supplied with easy to handle masterbatch, with the help of coating and adding stabilizer to reduce the release of red phosphorus. Red phosphorus not only has a strong flame retardant effect, but also can form a synergistic flame retardant system with other substances to improve the flame retardant efficiency. It is reported that Japanese nicao company and another flame retardant company have jointly developed a new flame retardant based on thermal expansion graphite and red phosphorus

ammonium polyphosphate is mainly used as expansion catalyst. The expansion formula of ammonium polyphosphate and carbonaceous nitrogen-containing resin has found industrial application. Clariant company introduced a kind of high-efficiency intumescent p-n flame retardant, which is especially suitable for PP and reinforced PP, and the brands are exolit ap750 and ap751. The halogen-free flame retardant PP and halogen-free flame retardant reinforced PP are used in Western Europe to replace the flame-retardant ABS or flame-retardant ABS/PC in the manufacture of some electronic components, which can obtain high-efficiency and low-cost effects. In addition, some new hypophosphite additives produced by Clariant have significant effects on thermoplastics, especially polyester and ABS

organophosphorus flame retardants are characterized by their dual functions of flame retardancy and plasticization, which can make the flame retardants completely halogen-free and improve the flow processing performance of plastics during molding. It can inhibit the residue after combustion and produce less toxic and corrosive gases than halogen flame retardants. In addition, it has good compatibility with the resin and maintains the transparency of the resin. Organophosphorus flame retardants are developing towards high functionality and high added value

the new tetraaryl arylidene diphosphate has been used in thermoplastic industry. It may have gas phase effect, but it may also produce barrier layer. It is mainly used in some high-function styrene copolymers, such as PPO/hips and PC/ABS. DSM's melamine polyphosphate melapur200 used in polyamide 66 has higher thermal stability than the existing melamine polyphosphate. It is used in flame-retardant glass fiber filled nylon 66 and adopts higher processing temperature

the study found that the use of synergists can effectively improve the flame retardant effect of phosphides. For example, n-p synergistic mechanism, there are also various metal oxides and salts that have synergistic effects with phosphorus, but sometimes have antagonistic effects, such as (Zn) 3 (BO3) 2, Fe2O3 and MoO3 are effective, while sn0, pb0 and Bi2O3 are harmful, and the combination of phosphate ester and antimony trioxide is often antagonistic

3. Nitrogen series

nitrogen series flame retardants are relatively late in development compared with other flame retardants. Their flame retardancy is not very good, and they are often used in combination with other flame retardants. The addition of nitrogen system can promote the carbonization of phosphorus system and has synergistic effect. As mentioned above, DSM's melamine polyphosphate melapur200. In addition, nitrogen system and antimony system also have synergistic effect

nitrogen flame retardants mainly include melamine and melamine cyanurate, which can be used in polyurethane and polyamide. In addition, there are melamine formaldehyde condensate, guanidine salt, guanidine condensate, etc. Guanidine sulfamate in guanidine compounds is low toxic and soluble in water. It is mainly used in wallpaper

at present, the development of nitrogen flame retardants with high nitrogen content, high temperature decomposition and matching with polymers is its main research topic

4. Silicon system

in recent years, silicon system has attracted worldwide attention as a low harmful flame retardant

inorganic silicon is mainly SiO2, which has both reinforcement and resistance. Friendship tips for quality control: if there are unclear places, incoming inspection, physical property experiments, mechanical research, and the basic equipment of material development, its flame retardant mechanism is that when plastic burns, it forms a silicon dioxide coating, which plays a dual role of heat insulation and shielding. SiO2 is rarely used alone, and is often used together with halides. The research, development and use of organosilicon have long attracted attention. As a kind of polymer flame retardant, it has the characteristics of high efficiency, non-toxic, low smoke, anti dripping, no pollution, etc. especially because it is a polymer material, it has little impact on the performance of products, and it is a kind of promising organic flame retardant. Its flame retardant mechanism is: when the plastic is burning, silicone generates silicon carbide. This silicon carbide isolation layer can prevent the volatiles generated by combustion from escaping, isolate oxygen from contacting the resin, and prevent the melt from dripping, so as to achieve the purpose of flame retardant

silicone flame retardants mainly include silicone oil, silicone resin, silicone rubber and organosilane alcohol amide. Ge sfr-100 has a good flame retardant effect on polyolefins, and improves the processing and mechanical properties of the resin. It can give the matrix excellent flame retardancy and smoke suppression. It is used in occasions where the fire safety is very strict and the ordinary flame retardant system is not applicable. Silicone micropowder developed by Dow cornimg company in the United States is a very efficient flame retardant. It can be used in polyolefin, polyester, polystyrene and nylon according to different models. Guanghua filler Chemical Co., Ltd. in Foshan, Guangdong Province, China has also developed organosilicon powder for flame retardant and marriage inhibition of various plastics. It can improve processability and plastic surface smoothness. In addition, the University of national defense science and technology used its rich experience in the field of composite materials to increase the oxygen index of the system by increasing the efficiency of Al (OH) 3/mg (OH) 2 with organosilicon

polysiloxane PC jointly developed by NEC and sumitomodow, a Japanese polycarbonate resin supplier, is one of the latest halogen-free flame retardant resins. This silicon flame-retardant PC has reached the certification of "Blue Angel" environmental protection mark in Germany and has been sold to manufacturers in electrical and other industries around the world

at present, the development of flame retardants has developed towards multi-function. People have paid more and more attention to improving flame retardant efficiency, reducing dosage and reducing harm to health and environment. Therefore, the halogen-free trend is becoming the main trend of the development and application of flame retardants

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