Polyethylene (PE for short) is a thermoplastic resin made from ethylene through polymerization. In industry, it also includes ethylene and a small amount of α- Copolymers of olefins. Polyethylene is odorless, non-toxic, feels like wax, has excellent low temperature resistance (the minimum use temperature can reach – 100~- 70 °C), good chemical stability, and can withstand the corrosion of most acids and alkalis (not resistant to acids with oxidizing properties). It is insoluble in general solvents at room temperature, with small water absorption and excellent electrical insulation.
brief introduction
Polyethylene was first synthesized by British ICI Company in 1922. In 1933, the British Bunemen Chemical Industry Company found that ethylene could polymerize under high pressure to produce polyethylene. This law was industrialized in 1939 and is generally known as the high-pressure law. 1953 K Ziegler found that with TiCl4-Al (C2H5) 3 as catalyst, ethylene can also polymerize under low pressure. This method was put into industrial production by Hurst Company of Germany in 1955, and is generally known as low pressure polyethylene. In the early 1950s, Philip Petroleum Company of the United States found that with chromium oxide aluminum silicate gel as catalyst, ethylene can polymerize under medium pressure to produce high-density polyethylene, and achieved industrial production in 1957. In the 1960s, DuPont Corporation of Canada began to use ethylene and α- Low density polyethylene (LDPE) was prepared from olefins by solution method. In 1977, Union Carbide and Dow Chemical successively adopted the low-pressure method to produce low-density polyethylene, which is called linear low-density polyethylene. Among them, the vapor phase method of Union Carbide is the most important. Linear low density polyethylene (LLDPE) has similar properties to low-density polyethylene (LDPE), but also has some characteristics of high-density polyethylene (HDPE). In addition, it has low energy consumption in production, so it develops very rapidly and becomes one of the most eye-catching new synthetic resins.
The core technology of low pressure method is catalyst. The TiCl4-Al (C2H5) 3 system invented by Ziegler in Germany is the first generation catalyst for polyolefins, with low catalytic efficiency. Every gram of titanium is about several kilograms of polyethylene. In 1963, Belgium Solvay Company pioneered the second generation catalyst with magnesium compound as the carrier, and the catalytic efficiency reached tens of thousands to tens of thousands of grams of polyethylene per gram of titanium. The adoption of the second generation catalyst can also save the post-treatment process of removing the catalyst residue. Later, gas phase high efficiency catalyst was developed. In 1975, Italy’s Monte Edison Group Company developed a catalyst that can directly produce spherical polyethylene without granulation. It is called the third generation catalyst, which is another revolution in high-density polyethylene production.
Polyethylene is very sensitive to environmental stress (chemical and mechanical action), and its heat aging resistance is inferior to the chemical structure and processing strip of polymer. Polyethylene can be processed by general thermoplastic molding method. It has a wide range of applications, mainly used to manufacture films, packaging materials, containers, pipes, monofilament, wires and cables, daily necessities, etc., and can be used as high-frequency insulation materials for television, radar, etc. With the development of petrochemical industry, polyethylene production has developed rapidly, accounting for about 1/4 of the total plastic output. In 1983, the total production capacity of polyethylene in the world was 24.65 Mt, and the capacity of the plants under construction was 3.16 Mt. According to the latest statistical results in 2011, the global production capacity 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.