1933, Bremen Chemical Industry Company of Britain discovered that ethylene can be polymerized under high pressure to produce polyethylene. This method was industrialized in 1939, commonly known as high-pressure method. In 1953, K. Ziegler of the Federal Republic of Germany found that ethylene can be polymerized at lower pressure with TiCl4-Al(C2H5)3 as catalyst. This method was put into industrial production by Hearst Company of the Federal Republic of Germany on 1955, commonly known as low-pressure polyethylene. In the early 1950s, Philip Oil Company of the United States found that ethylene could be polymerized under medium pressure to produce high-density polyethylene with chromium oxide-silica-alumina gel as catalyst, and it was industrialized in 1957. In 1960s, DuPont Company of Canada began to prepare low density polyethylene from ethylene and α -olefin by solution method. During the period of 1977, Union Carbide Company and Dow Chemical Company successively prepared low-density polyethylene by low-pressure method, which is called linear low-density polyethylene, and the gas phase method of Union Carbide Company is the most important. Linear low density polyethylene (LDPE) has similar properties to LDPE and some characteristics of high density polyethylene. In addition, because of its low energy consumption in production, it has developed rapidly and become one of the most striking new synthetic resins.
The core technology of low pressure method lies in catalyst. TiCl _ 4-Al (C2H5) _ 3 system invented by Ziegler in Germany is the first generation polyolefin catalyst, and its catalytic efficiency is low, with about several kilograms of polyethylene per gram of titanium. 1963 Solvi company in Belgium pioneered the second generation catalyst with magnesium compound as carrier, and the catalytic efficiency reached tens of thousands to hundreds of thousands of grams of polyethylene per gram of titanium. Using the second generation catalyst can also save the post-treatment process of removing catalyst residue. Later, a gas-phase high-efficiency catalyst was developed. 1975, Italy's Monte Edison Group Company developed a catalyst which can directly produce spherical polyethylene without granulation, and it is called the third generation catalyst, which is another revolution in the production of high-density polyethylene.
Polyethylene is a crystalline thermoplastic resin. Their chemical structure, molecular weight, degree of polymerization and other properties largely depend on the polymerization method used. The polymerization method determines the type and degree of branching. The crystallinity depends on the regularity of molecular chain and its thermal history.
Polyethylene is very sensitive to environmental stress (chemical and mechanical effects), and its thermal aging resistance is worse than that of polymer chemical structure and processing belt. Polyethylene can be processed by the molding method of general thermoplastics (see Plastic Processing). Widely used in the manufacture of films, packaging materials, containers, pipes, monofilaments, wires and cables, daily necessities and so on. , which can be used as high-frequency insulating material for TV and radar. With the development of petrochemical industry, polyethylene production has developed rapidly, accounting for about 1/4 of the total plastic production. 1983 The total global polyethylene production capacity was 24.65Mt, and the equipment under construction capacity was 3.16 mt. According to the latest statistics of 20 1 1, the global production capacity has reached 96 mt The development trend of polyethylene production shows that production and consumption are gradually shifting to Asia, and China is becoming the most important consumer market.
In nuclear physics, astrophysics and reactor operation, polyethylene is used as a diffusion agent for measuring neutrons. He made his own contribution to the study of nuclear physics.
Polyethylene is a kind of plastic. The convenient bag we often mention is polyethylene (PE). Polyethylene is the simplest polymer and the most widely used polymer material. It is formed by connecting repeated–-CH2-–units. Polyethylene is formed by addition polymerization of ethylene (CH2=CH2).
The properties of polyethylene depend on its polymerization mode. Under the catalysis of organic compounds, high density polyethylene was synthesized by Ziegler-Natta polymerization at medium pressure (15-30 atmospheric pressure). Under these conditions, the polymerized polyethylene molecules are linear, the molecular chain is very long and the molecular weight is as high as several hundred thousand. Low density polyethylene (LDPE) is produced by radical polymerization under high pressure (100-300MPa) and high temperature (190–210c) with peroxide as catalyst.