0 ITEM
The gap is huge! Special engineering plastics PPS
Special engineering plastics, also known as high-performance polymers, are generally developed according to the needs of special purposes. Compared with general engineering plastics, they have unique and excellent physical properties, and the long-term use temperature is above 150 °C. Special engineering plastics include polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polysulfone (PSF), polyimide (PI), polyarylate (PAR), liquid crystal polymer (LCP).
Due to the flame retardancy, high thermal stability, high mechanical strength and excellent electrical properties of special engineering plastics, they have been widely used in high-tech industries such as electronics, automobiles, aerospace, precision instruments, and 5G communications. Special engineering plastics also have broad application potential in smart clothing, smart medical and other fields.
Introduction of PPS resin
Polyphenylene sulfide (PPS) is an important semi-crystalline thermoplastic resin. The main chain of the PPS molecule is formed by alternately connecting benzene rings and sulfur atoms, and there is no side chain, so it has better chain symmetry and regularity, so that it has better crystallization ability. The rigid structure of the benzene ring on the main chain makes the molecular chain relatively rigid, the glass transition temperature is around 85°C, the creep value is low, and the elastic modulus is high.
The molecular structure of PPS contains highly stable chemical bonds, forming a thermally stable crystal lattice, which makes it highly molecularly stable to thermal degradation and chemical reactions. The thermal deformation temperature of PPS is generally greater than 260 °C, which can be Use in the temperature range of 180~220℃.
In addition, the electrical properties of PPS are very outstanding. Compared with other engineering materials, its dielectric constant and the tangent of the dielectric loss angle are relatively low, and it does not change much in a large frequency, temperature and temperature range; in addition, it has High rigidity, dimensional stability, good processing performance and so on. Due to the high rigidity, it is necessary to increase the toughness or impact strength by adding fillers or copolymerizing modification.
PPS resin synthesis method
Polyphenylene sulfide (PPS) has many synthetic methods, such as: Phillips method, sulfur solution method, oxidative polymerization method, p-halogenated thiophenol melt or solution polycondensation method, hydrogen sulfide method and so on. Three methods are described below:
1.Phillips method (sodium sulfide method):
This method is the earliest method for industrial production of PPS in the world, and it is also one of the most important industrial production methods at present. It is to use the basic equimolar ratio of p-dichlorobenzene and anhydrous sodium sulfide, in polar organic solvent, under nitrogen protection at 170-350 ° C, under the pressure of 6.87MPa to polymerize, and generate linear polyphenylene sulfide through condensation reaction. Solution polycondensation of ethers. Commonly used polar organic solutions include amides, lactams and sulfones.
The method has short process route, high yield and stable product quality.
2. Sulfur method:
Developed by the team of Professor Chen Yongrong from Sichuan University. PPS is produced by polycondensation of p-dichlorobenzene and sulfur in hexamethylphosphoric triamide or N-methylpyrrolidone in the temperature range of 175-250°C under normal pressure. The reaction is carried out in two steps. First, sulfur is reduced to S2- by reacting with a reducing agent and auxiliary agent in a polar organic solvent, and then S2- is polymerized with p-dichlorobenzene at atmospheric pressure.
The method avoids the problems of oxidation and moisture absorption of sodium sulfide in storage, and at the same time saves the dehydration step of the sodium sulfide method, shortens the production cycle, and reduces energy consumption. The sulfur method is also one of the most important industrial production methods at present.
3. Oxidative polymerization method:
Proposed by E.Tsuchida and K.Yamamoto of Waseda University, it is called an epoch-making manufacturing method. Diphenyl disulfide is used, oxygen is used as oxidant, Lewis acid is used as catalyst, and PPS is prepared by reaction at normal temperature and pressure.
The yield of this method is close to 100%, the reaction conditions are mild, and the product is a completely linear straight-chain structure. However, the molecular weight of the prepared PPS is not high enough, and there are still a small amount of disulfide bonds in the product structure, so it cannot be industrially produced.
PPS engineering plastics:
More than 80% of the amount of polyphenylene sulfide is realized by the composite reinforced modified material made of reinforcing fibers or fillers. In addition, polyphenylene sulfide and other high polymers can also be blended and modified. Preparation of polyphenylene sulfide to improve its toughness and impact strength to expand its use.
At present, the main varieties are PPS/PA (polyamide), PPS/PBT (polybutylene terephthalate) and PPS/PTFE (polytetrafluoroethylene). PPS plastics are widely used in the automotive industry and can be used in the production of automotive brakes, guide systems, lamp holders, radiator parts and other parts. PPS plastics are also widely used in the electrical and electronic industry. They are often used in the manufacture of electrical sockets, relays, electronic instrument panels, and capacitor protective covers; they can also be used in the manufacture of microelectronic parts, such as capacitors, resistors, etc.; they can also be used in home appliance parts, Such as iron, electric cooker, microwave oven parts.
PPS film:
The film-grade PPS melt is extruded to form a sheet with a thickness of 0.1-2 mm, and then biaxially stretched to obtain a polyphenylene sulfide film with a thickness of 1-100 μm. Because of its excellent insulating properties, PPS film is mainly used in electrical insulating materials, electronic components, and can improve the efficiency of machines. In terms of 5G communication, the application of PPS film in flexible printed circuits will reduce the transmission loss of communication equipment in high frequency bands. Second, it will help stabilize high-speed communications across temperature and humidity ranges, enabling fast data transfer rates for 5G.
PPS fiber:
PPS fiber is mainly used as a special functional filter material, mainly used in thermal power plants, coal-fired boilers, waste incinerators and heating coal-fired boiler dust filter fabrics. In addition, it can also be used as canvas for dryer, sewing thread, various protective cloths, anti-fog materials, radiation-resistant materials, high-temperature flame-retardant protective clothing, etc. PPS fiber can be made into ultra-fine denier PPS fiber to improve the filtration accuracy and filtration performance of the filter material. It can also be modified or blended with polyamide, carbon black and other materials to improve the toughness of PPS fiber. Wear resistance and longevity.
At present, the production companies of PPS are mainly distributed in China, Japan, the United States, Germany and other countries. The total production capacity of PPS in Japan and the United States accounts for more than 60% of the world's total. Japan's Toray Toray Company, Kureha Kureha Chemical Company, DIC Company and American Phillips Company have more than 40 years of experience in developing PPS technology. PPS products are rich in variety, large in production scale and high in product quality.
In 2020, China's demand for PPS is 63,500 tons, accounting for about half of the world's total, and the demand is increasing year by year. However, the domestic production of PPS in 2020 is 58,900 tons, which cannot meet the huge demand, and many domestic PPS products rely on imports. The main reason is that the quality of domestic PPS is also slightly lower than that of PPS made in Japan and the United States, and for some PPS products, most domestic enterprises cannot produce them, and many process technologies are still being explored.
Therefore, my country also needs to strengthen the research and development of PPS product types, realize the differentiated production of PPS, and at the same time need to find the optimal production process. my country's PPS production enterprises can analyze and compare the related patents of Toray and Philips, find out the gap between their production processes, and improve and optimize equipment and process routes to reduce the production costs of Chinese enterprises, Improve product performance, develop new products with high performance and specificity, and improve their market competitiveness.
