Published April 1968
The basic patent on polyethylene was issued to Imperial Chemical Industries Ltd. (ICI) in 1937, by which time a continuously running pilot plant was in operation. In 1938 and 1939 polyethylene was evaluated for insulation of submarine cable. Full-scale production was under way in the United Kingdom early in 1942 and in the United States in 1943.
In Germany investigation of ethylene polymerization started in 1938 and led to construction in 1942 of a plant at Zweckel to make 10-20 tons per month of Lupolen N, a low-molecular-weight (waxy) product. At the end of the war in Europe, (May 1945) a plant to produce 5 tons per month of Lupolen H, a high-molecular-weight product, was nearly complete at Gendorf.
The reaction discovered by ICI for producing polyethylene requires high pressures (1000-3000 atm) and high temperatures (150�C-230�C), and proceeds by a free-radical mechanism of polymerization. The product is a partially crystalline (60-70%) polymer containing about two chain branches per hundred carbon atoms. The number of branches determines the crystallinity and density. Densities of high pressure polyethylenes, usually in the range of 0.91-0.93, are classified as low." Modifications of the high pressure process have led to polymers of medium density" in the range of 0.93-0.94. Quite different processes are employed to produce polyethylenes of higher density (0.94 to 0.97), which have crystallinities above 7.5% and which are essentially linear in structure.
Low-density polyethylenes are produced commercially at high pressures in processes employing either tubular or autoclave reactors. In this report two conventional processes, one employing a tubular reactor and one employing an autoclave, have been evaluated. Additionally, a process is evaluated that employs gamma-radiation-induced polymerization.
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