[Background and Overview][1][2]
Red phosphorus is an allotrope of yellow phosphorus and is relatively stable in the air. It is a non-metallic material with relatively active chemical properties and has been widely used in industrial and agricultural production. As a flame retardant material that can be directly used as a single-effect flame retardant, its research and application are favored by researchers at home and abroad. Especially as an important raw material for the military industry, its excellent performance has attracted the attention of various countries. Red phosphorus is easy to absorb moisture, oxidize, and has high friction sensitivity. A lot of research has been conducted on it at home and abroad. As the only unique type of inorganic flame retardant, red phosphorus not only has high effective phosphorus content, good flame retardant effect, and can better maintain the mechanical and physical properties of the solvent dye manufacturer’s polymer, but is also applicable to a wide range of resins. Plant, the toxicity of red phosphorus is very low, and its half-lethal dose to rats is more than 15,000mg/kg. As a safe match agent, it often comes into contact with human skin and even children’s oral mucosa. There have never been reports of toxic hazards. Therefore, red phosphorus is used in the field of polymer flame retardancy and has sufficient health and safety guarantees. The disadvantage of red phosphorus as a flame retardant for polymers is that it may release toxicity when heated. The problems of gas and poor compatibility with resin can be minimized through modification to meet the processing requirements of the polymer.
my country’s red phosphorus production capacity already has a large excess, the economic benefits are not high, and it is easy to produce pollution. In recent years, the opportunities for production expansion mainly come from the transfer of production capacity from developed countries. For example, in 2002, the Nan Phosphorus Group introduced a complete set of Italian technology. Songming Company has built a 2000t/a red phosphorus production line and 100% of its products are exported. Therefore, it is recommended that enterprises that want to expand production capacity choose to introduce foreign technology and equipment so that their products can be exported. The main market for future expansion of production is still abroad. In the future, we should improve the technical level, improve product quality, and reduce costs; increase development efforts, develop new varieties, new brands, and new applications; and actively expand exports.
[Flame retardant mechanism][2]
The flame retardant mechanism of red phosphorus on polymers is similar to that of other phosphorus flame retardants. It is generally believed that red phosphorus first decomposes thermally during the polymer combustion process, or takes away oxygen from the main chain of the oxygen-containing polymer to form a phosphorus oxygen group, and cross-links with the polymer on the burning surface to form a phosphorus-oxygen cross-linked carbonization layer; or it interacts with the environment Oxygen generates oxygen-containing phosphoric acid (mainly metaphosphoric acid). This oxygen-containing grade is extremely hygroscopic and ultimately leads to carbonization of the surface of the burning polymer. The existence of the carbonized layer on the polymer surface can, on the one hand, isolate the polymer and reduce the release of flammable volatile components; on the other hand, it also has an endothermic effect, reducing the oxidation heat of the polymer itself, thereby achieving the purpose of solid-phase flame retardancy. At the same time, after the PO· free radicals, the pyrolysis product of red phosphorus, enter the gas phase, they can still capture a large number of H·, HO· radicals in the combustion flame, cut off the flame oxidation chain reaction, and play a gas phase flame retardant role.
[Features][3]
Red phosphorus is a purple-red powder that easily catches fire after friction. Does not emit phosphorescence in dark places. Soluble in anhydrous liquor, insoluble in water. When burning, it emits toxic and irritating phosphorus oxide fumes, which can form explosive mixtures with chlorate, nitrate, perchlorate and permanganate. It is also prone to explosion if heated or left in a humid place for a long time. Relative density: 2.34; sublimation temperature: 416°C; melting point: 590°C (43 atmospheres), autoignition point: 260°C (in air). Store in a cool and dry place, separated from oxidants and acids. This product will slowly oxidize when in contact with air, forming oxides that easily absorb water, so it should be stored in a sealed container. Avoid sun exposure and keep away from fire and heat sources. Handle it with care when transporting to prevent vibration and friction. Be careful to prevent the powder from scattering. If leakage is found, mix it with yellow sand and sweep it away. It takes a while for red phosphorus to burn from smoking to catching fire, so it can be rescued. In case of fire, extinguish it with water first and then cover it with sand. Firefighters should wear gas masks. When using water, they should pay attention to the flow direction of the water and the disposal of the site after red phosphorus is lost to prevent re-ignition. In addition, under certain conditions of high temperature, red phosphorus can be converted into more dangerous yellow phosphorus, so it is necessary to Get attention.
[Production process][1]
The method of producing red phosphorus is to put yellow phosphorus into an iron conversion kettle, basically isolate it from the outside air, slowly increase the temperature, and heat it at 240 to 260°C for several days. The stage from semi-solid phosphorus to liquid phosphorus is exothermic, so careful attention must be paid to temperature regulation. In the final stage, it is heated at about ℃ for several hours and then allowed to cool. After cooling, the obtained red phosphorus is crushed in water, and a small amount of sodium hydroxide is added for heating. The unconverted yellow phosphorus decomposes into phosphine and phosphite and is removed. After washing with water, dehydration and drying, the finished product is obtained.
[Application][2][4]
Red phosphorus is mainly used in the production of matches, fireworks, phosphoric acid, phosphoric anhydride, phosphorus pentachloride, phosphorus trichloride and phosphorus bronze. It is also used in the manufacture of pesticides such as aluminum phosphide and zinc phosphide, and Used in organic synthesis, medicine, synthetic material flame retardants, military incendiary bombs, etc.
1. Application of red phosphorus in oxygen-containing resin
Red phosphorus, as a flame retardant, tended to be used in the field of flame retardant oxygen-containing resins in the early days. Following Bayer’s first use of red phosphorus in polyurethane foam products,When combined with other system flame retardants, the synergistic effect is excellent. Generally speaking, the combination of red phosphorus and halogen, aluminum hydroxide, and magnesium hydroxide flame retardants can greatly reduce the total amount of flame retardants added, thus avoiding the disadvantages of traditional flame retardant systems that may lead to a decrease in the physical parameters of the product. . At the same time, this flame retardant system can also minimize the amount of smoke produced when polymer products are burned, so it is expected to become a mainstream in the development of non-halogenated flame retardant systems in the future.
[Microencapsulation][2]
In view of the disadvantages of red phosphorus being directly used as a polymer flame retardant, such as strong surface hygroscopicity, poor storage stability, and poor compatibility with resins, flame retardant development and application companies around the world have conducted modification research. , proposed many effective solutions. In summary, there are two main technologies: adding stabilizing additives and surface microencapsulation technology.
1. Add stabilizing additives: necessary oxidation inhibitors and PH3 capture agents are added during the preparation or application of red phosphorus to maximize the safety of red phosphorus flame retardants. and operability. Although this treatment method is simple and easy to implement, and can alleviate and inhibit the oxidation of red phosphorus and the release of PH3 to a certain extent, it cannot fundamentally solve the problems of strong hygroscopicity and poor operational stability. . The early treatment method of adding stabilizing additives has rarely been adopted by the application industry.
2. Red phosphorus surface microencapsulation technology: It is a new method developed in the late 1970s. Its principle is to coat the surface of red phosphorus with a continuous and dense layer of organic or inorganic PVC resin through physical or chemical methods. The protective film “packages” the red phosphorus particles to form microencapsulated red phosphorus flame retardant. This kind of microencapsulated red phosphorus not only overcomes the shortcomings of commercially available red phosphorus such as strong hygroscopicity during storage and use and easy release of PH3 during thermal processing, but also improves the performance of red phosphorus flame retardants and polymers. The compatibility of the resin is beneficial to improving the processability and mechanical and physical properties of the complex. Only when the polymer burns and the bladder material ruptures can red phosphorus exert its flame retardant effect. The treatment methods of microencapsulated red phosphorus can be divided into the following three categories according to the different coating materials: inorganic coating method, organic coating method and inorganic-organic double-layer coating method.
[References]
[1] Wang Daquan, editor-in-chief. Fine Chemical Dictionary. Beijing: Chemical Industry Press. 1998. Page 67.
[2] Wang Kezhi, Wang Ailian. Red phosphorus flame retardant and its application[J]. Modern Plastics Processing and Application, 1993, 5(4): 26-30.
[3] Liu Dingming, Yang Jinping, eds. Technical Dictionary of Container Transport Business Volume 2. Beijing: People’s Communications Press. 1996
[4] Chen Yuyun, Huang Deyong. Analysis of red phosphorus market prospects[J]. Yunnan Chemical Industry, 2004, 31(3): 14-15.
[5] Ju Jianfeng, Su Guangjun. Study on the stability of red phosphorus[J]. Journal of Nantong Institute of Technology: Natural Science Edition, 2003, 2(3): 25-27.
