It is a member of the important family of polyolefin resins. It is the most widely used plastic in the world, made into products ranging from clear food wrap and shopping bags to detergent bottles and car fuel tanks. It can also be cut or spun into synthetic fibers or modified to assume the elastic properties of a rubber.
Ethylene (C2H4) is a gaseous hydrocarbon commonly produced by the cracking of ethane, which in turn is a major component of natural gas or can be distilled from petroleum. Ethylene molecules are essentially composed of two methylene units (CH2) joined together by a double bond between carbon atoms, a structure represented by the formula CH2 = CH2. Under the influence of polymerization catalysts, the double bond can be broken and the resulting extra single bond is used to attach to a carbon atom in another ethylene molecule. Therefore, transformed into the repeating unit of a large polymeric (multi-unit) molecule, ethylene has the following chemical structure:
Molecular structure..
This simple structure, repeated thousands of times in a single molecule, is the key to the properties of polyethylene. Long, chain- shaped molecules, in which hydrogen atoms are connected to a carbon backbone, can be produced in a linear or branched form. The branched versions are known as low density polyethylene (LDPE) or linear low density polyethylene (LLDPE); The linear versions are known as high density polyethylene (HDPE) and high molecular weight polyethylene (UHMWPE).
The basic composition of polyethylene can be modified by the inclusion of other elements or chemical groups, as in the case of chlorinated and chlorosulfonated polyethylene. Furthermore, ethylene can be copolymerized with other monomers such as vinyl acetate or propylene to produce a series of ethylene copolymers. All these variants are described below.
History
Low-density polyethylene was first produced in 1933 in England by Imperial Chemical Industries Ltd. (ICI) during studies of the effects of extremely high pressures on polyethylene polymerization. ICI was granted a patent on its process in 1937 and began commercial production in 1939. It was first used during World War II as an insulator for radar cables.
