Polyethylene (PE for short) is currently the most produced high-quality polymer material, and polyethylene plastic ranks first in the world’s total plastic production. Polyethylene is odorless, non-toxic, feels like wax, has excellent low-temperature resistance (the lowest operating temperature can reach -100~-70°C), has good chemical stability, and is resistant to most acids and alkalis (not resistant to oxidation). properties of acids). It is insoluble in general solvents at room temperature, has low water absorption and excellent electrical insulation properties. Polyethylene can be processed using general thermoplastic molding methods. It has a wide range of uses, mainly used to make films, packaging materials, containers, pipes, monofilaments, wires and cables, daily necessities, etc., and can be used as high-frequency insulation materials for televisions, radars, etc.
The classification of polyethylene is as follows:
1. Low-density polyethylene, referred to as LDPE, is usually produced by high-pressure method, so it is also called high-pressure polyethylene. Density 0.910~0.925g/cm3, melting point 107~126℃, it has the advantages of light weight, cold resistance, impact resistance, chemical resistance, excellent high frequency insulation performance and processing performance, and can be blow molded, extruded, and injection molded. . Used for packaging materials, pipes, cable insulation and sheathing. Polyethylene films are widely used in seedling cultivation, mulching films, vegetable greenhouses and food packaging. Polyethylene sheets are good corrosion-resistant lining materials.
2. High-density polyethylene, referred to as HDPE, is usually produced by the low-pressure method, also known as low-pressure polyethylene, with a density of 0.941~0.965g/cm3, a melting point of 132~135°C, and a high use temperature. Chemicalbook hardness, mechanical strength and chemical resistance properties. Various bottles, cans, basins, barrels and other containers, as well as ropes, fish nets, strapping tapes, wires, cable coverings, pipes, plates and special-shaped materials can be made by blow molding, injection molding and extrusion.
3. Medium-density polyethylene, with a density of 0.926~0.940g/cm3, is also called medium-pressure polyethylene or Phillips polyethylene, and its performance is similar to high-density polyethylene. Domestic production is small, so it is omitted here.
4. Linear low-density polyethylene, referred to as LLDPE, has a density of 0.92 to 0.93g/cm3 and a melting point of 117 to 130°C. The impact strength, elongation, and environmental stress cracking resistance of linear low-density polyethylene are Good sex. It has the best puncture resistance among polyethylenes and is particularly suitable for the production of thin Chemicalbook films, stretched products, etc. The advantages and characteristics of linear low-density polyethylene are increasingly recognized and valued by people. Adding an appropriate amount of linear low-density polyethylene to films, filaments, tapes, pipes and other products and blending them with other resins can significantly improve the performance of plastic products. tensile strength, impact properties, etc.
5. The catalyst used in the polymerization reaction of metallocene polyethylene is metallocene type, so it has unique properties. It is referred to as m-PE in English and is a new type of polyethylene with excellent properties. A catalytic system composed of a metallocene catalyst and a methylaluminoxane cocatalyst is used for the polymerization of ethylene. The resulting polyolefin product obtains many unique properties that traditional polyethylene has never had, such as high relative molecular mass and narrow distribution, branched Short and few chains, low density, high purity, high tensile strength, high transparency, high impact, puncture resistance, low heat sealing temperature, etc. This is because the metallocene catalyst has an ideal single active site, which allows precise control of the relative molecular mass, relative molecular mass distribution, comonomer content, and its distribution on the main chain and crystal structure. Metallocene polyethylene has high stereoregularity and narrow relative molecular mass distribution, and belongs to a new type of polyethylene.
