Polyethylene, << `pol` ee EHTH uh leen, >> is a major synthetic polymer, an essential ingredient of plastics. Polyethylene plastic products include milk jugs, oil bottles, and plastic bags. About a third of all synthetic polymers produced in the United States are polyethylenes.
There are three main types of polyethylene: high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE). HDPE is the toughest and most rigid type. Manufacturers form it into such products as bottles and jugs. LDPE and LLDPE are relatively soft and flexible. Manufacturers produce them as thin films. One use of LDPE is as bread bags. Garbage bags are made of LLDPE, which is stronger than LDPE.
A polymer is a long, chainlike molecule. The “links” are repeating patterns of simple groups of atoms called monomers. Polyethylene is made from ethylene monomers, each consisting of two carbon atoms and four hydrogen atoms.
Manufacturers make polyethylene by mixing a solution of ethylene gas with a catalyst, a substance that speeds a chemical reaction without being used up by the reaction. Many polyethylene plastics contain special ingredients, such as colorings and a substance that prevents film from sticking to itself.
Polyethylene melts at temperatures of 230 to 300 °F (110 to 150 °C). It can be melted and re-formed again and again, so it is easy to recycle.
Imperial Chemical Industries (ICI) of Great Britain first produced polyethylene in 1939. It was expensive to make, so little was produced until the 1950’s, when less expensive manufacturing techniques were developed.
