PPS has a symmetrical rigid backbone and is part of a crystalline polymer composed of repeating para-substituted benzene rings and sulfur atoms.
Polyphenylene sulfide is a new type of functional engineering plastics. Its molecules contain repeating structural units of p-phenylene sulfide, and the main chain of the molecule contains phenylene sulfide. Its molecular weight is 10,000~50,000. Polyphenylene sulfide is a linear or branched polymer with no crystalline melting point. It is a linear structure before cross-linking and a thermosetting structure after cross-linking. It can be softened to a certain extent when fully heated and cooled.
Polyphenylene sulfide is polycondensed from sodium sulfide and dichlorobenzene in a strong polar solvent. The production methods include Michael's method, p-halogenated thiophenate self-condensation method, aromatic polyhalide and alkali metal sulfide solution polycondensation method, etc.
The relative density of polyphenylene sulfide is 1.36, and the resin is white powder or granules, hard and brittle, with high crystallinity and strong melt viscosity. Polyphenylene sulfide has two types of molecular weight, low molecular weight and high molecular weight. Due to the high melt flow value, it is difficult to mold directly, so in addition to spraying, other methods must undergo a certain degree of cross-linking during molding, and a certain amount of glass fiber or inorganic resin for injection molding, molding and extrusion molding must be mixed. in the stuffing. High molecular weight polyphenylene sulfide does not need to be cross-linked and can be directly used in the processing of plastic products.
PPS has a symmetrical rigid backbone and is part of a crystalline polymer composed of repeating para-substituted benzene rings and sulfur atoms. PPS is a special engineering plastic with high performance and a high melting point of up to 280 °C that can replace metals. It is located at the top of the polymer performance pyramid, as shown in Figure 1. For this reason, based on the excellent performance of PPS resin, it meets the material requirements of demanding engineering plastics projects.
1.Characteristics of High Performance Polyphenylene Sulfide Resins
1. High-performance PPS resin is a crystalline polymer with high hardness. Its crystal content is about 65%. Fast crystallization speed, good fluidity and short molding cycle.
2. Excellent heat resistance. Its melting point can reach 275~291°C, heat distortion temperature is 135°C, and the heat distortion temperature after glass fiber strengthening can reach 260°C. In air and nitrogen, the initial and weakening temperature of polyphenylene sulfide is about 400°C, it decomposes in air at 700°C, and can still maintain 40% of its weight in inert gas at 1000°C. The long-term use temperature is 200~240°C, and the gas barrier thermal resistance and long-term continuous use thermal stability are superior to all current engineering plastics.
3. It has good mechanical properties. It has extremely high rigidity, high surface hardness, little decrease in rigidity under high humidity conditions, and has excellent creep resistance, fatigue resistance and wear resistance. Its wear resistance can be improved by filling lubricants such as fluororesin and carbon fiber. And greatly improved.
4. It has excellent corrosion resistance and chemical resistance. In addition to strong oxidizing acids (such as concentrated sulfuric acid, nitric acid, etc.), it can also withstand the corrosion of other acids, alkalis and salts, and is insoluble in any organic solvent below 200 ° C. Its corrosion resistance is almost equivalent to that of polytetrafluoroethylene. In addition, PPS also has good weather and radiation resistance, and its performance will not be affected by multiple strong ultraviolet and gamma-ray irradiation and neutron radiation.
5. It has a small water absorption rate (only 0.008%) and oil absorption rate. Small molding shrinkage and linear expansion coefficient, the product has stable dimensions and small deformation, and can still maintain dimensional stability even in some humid, oily and corrosive gas environments, so it can be used for precision molding.
6. Excellent electrical properties. High-performance PPS resin has little change in volume resistivity under high temperature and high humidity, and its dielectric constant changes little with temperature and frequency. In addition, the content of ion impurities is low, and it can be immersed in a solder bath at 260 ° C, so it can withstand surface soldering Thermal shock of electronic components, suitable for products with extremely high requirements on electrical performance. It has high resistivity and low dielectric properties.
7. High-performance PPS resin has extremely low melt viscosity and good fluidity. It is easy to wet and contact with glass fiber, so it is easy to fill. The glass fiber or glass fiber-inorganic filler reinforced injection molding pellet prepared by it has high impact resistance, bending resistance and ductility.
8. High-performance PPS resin has very high bonding strength to glass, aluminum, stainless steel, etc. The bonding strength to glass is even greater than that of glass.
2. Overview of Engineering Plastics Varieties
Engineering plastic is a kind of plastic material that can withstand mechanical stress for a long time as a structural material, and can be used in a wide temperature range and in a harsh chemical and physical environment. Compared with general plastics, engineering plastics have more excellent mechanical properties, electrical properties, chemical resistance, heat resistance, wear resistance, dimensional stability, etc., and compared with metal materials, they are light in weight and convenient for complex Product design, low energy consumption during molding and other advantages. Engineering plastics are widely used in industrial sectors such as electronics, construction, automobiles, machinery, and aerospace. Engineering plastics are divided into two categories: general-purpose engineering plastics and special-purpose engineering plastics according to the amount, performance and scope of application.
Among them, general engineering plastics mainly include nylon (PA), polycarbonate (PC), polyoxymethylene (POM), polybutylene terephthalate (PBT), polyphenylene oxide (PPO), etc. Polymethylmethacrylate (PMMA) is a rapidly growing plastics application.
3. Application of High Performance PPS Resin in Engineering Plastics
As an engineering plastic, PPS molding materials have many excellent properties and can replace metals, thermosetting resins, etc., and are widely used in various fields for this reason.
(1) Application on auto parts
The use of auto parts is the most widely used field of PPS in the future. As shown in Figure 2, PPS is applied to electric drive unit components. Because PPS not only has outstanding continuous heat resistance, chemical resistance (gasoline, engine oil, etc.)
At present, in addition to PPS can replace the metal parts and phenolic resin used in the past, the application of PPS in new purpose parts is accelerating. Especially in terms of driving, braking, fuel, lighting, cooling parts centered on engine-related machines, and control parts that control these machines.
(2) Application to residential facilities/OA/precision equipment
"Superhard PPS (40% GF)" is often used in water-related equipment such as water heaters in residential equipment. This is because "ultrahard PPS (40% GF)" not only has the hot water resistance of PPS, but also has the characteristics of pressure resistance and good toughness. It is gradually replacing metal materials and deformed PPE materials represented by brass in the past.
"Modified PPS (30%GF)" which is good for dimensional accuracy due to its low crystallinity is suitable for precision equipment parts. At the same time, due to its excellent low-friction and low-wear properties, it is suitable for projects with special requirements for sliding characteristics, such as gears and bearings.
In terms of laser copiers, printers, etc., it is often used not only for its heat-resistant and fixing properties, but also for other special types, such as sliding around gears or bearings, and conducting electricity. Among them, the application of PPS in residential facilities/OA/precision equipment.
(3) Application on electrical/electronic components
In addition to high heat resistance, precision molding, and dimensional stability in the SMT process, PPS also has a high flame retardancy that can reach UL-94V-0 without adding flame retardants. These characteristics can be called the best molding materials for electrical/electronic parts represented by connectors. Glass fiber-reinforced/non-reinforced cross-linked type PPS and linear PPS low-burr type are mainly used, which have the general characteristics of PPS and appropriate formability, and are suitable for sophisticated and complex molded products such as connectors.
In addition, glass fiber/mineral filled cross-linked PPS and linear PPS are suitable for optical oscilloscopes, such as requirements for dimensional stability and rigidity. Ultra-low pressure formable PPS is suitable for the sealing of microcoils and electronic components.
(4) Application in machinery industry and chemical industry
In recent years, PPS has been chemically modified and mixed with glass fiber, mineral filler or carbon fiber to form a composite material, which is also widely used in the machinery industry and chemical industry.
(5) Applications in the field of lithium batteries
Lithium battery refers to a battery containing lithium in the electrochemical system. Due to the relatively active chemical properties of lithium metal, the environmental requirements for its processing are very high, which is why lithium batteries have not been used on a large scale. With the advent of the information age, microelectronics technology characterized by small size, light weight, high reliability, and fast working speed has developed and grown. While small and refined equipment is increasing, the requirements for batteries are also increasing. , Lithium batteries have entered the stage of widespread use. Polyphenylene sulfide (PPS) has excellent heat resistance, insulation, electrical properties and other characteristics, which meet the requirements for materials in the field of lithium batteries, and is the "intimate companion" of lithium batteries.
(6) Application in the field of environmental protection
The main emission sources of waste gas and waste dust are iron and steel plants, waste incinerators, thermal power plants, cement plants, carbon black plants and other fields. The waste gas and waste dust produced have problems such as high temperature, high humidity, and corrosion, which require dust removal materials to have strong high temperature resistance and corrosion resistance.
The fiber-grade PPS has high thermal stability and can be used continuously at 200-240°C. Even if it is placed at a high temperature of 260°C for 1000 hours, it can still maintain 60% of its strength. The corrosion resistance of PPS is similar to that of polytetrafluoroethylene, which is known as the "King of Plastics". In terms of flame retardancy, PPS fiber products are non-flammable and can meet the UL-94V-0 standard without adding flame retardants. . Therefore, the application of PPS fiber products in the above fields can greatly improve the service life of dust removal equipment. Among them, the most widely used product is the dust filter bag.
High-performance polyphenylene sulfide resin is widely used in engineering plastics projects such as electronic appliances, construction, automobiles, machinery, Aerospace and other industries, but the following aspects should be paid attention to when performing PPS molding operations:
(1) Pre-drying. Changes in hue and fluidity occur when the pellets are dried at too high a temperature or dried longer than necessary.
(2) Set the barrel temperature. A reasonable barrel temperature is generally set between 300~340°C, do not heat above 350°C, especially for products mixed with PTFE (fluororesin), the temperature range is 290~320°C, do not exceed 330°C.
(3) Residence time in the barrel. Generally, it is set within 60 minutes at 300°C, and within 30 minutes at 320°C.
(4) In the event of resin decomposition or similar situations, it is necessary to lower the temperature of the barrel to discharge the remaining resin in the barrel. When molding is stopped, after discharging the residual resin in the cylinder, please turn off the heater power.
