Plastic Extrusion Lineabout Raw Material
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 resin
(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.