Polyethylene tubing is a type of flexible piping which is commonly used in laboratories, as well as for transporting water, including drinking water. Its main component, polyethylene, is a polymer chain made of ethylene molecules, which consist of carbon and hydrogen. It can be made in different densities depending on the manner in which it will be used. Polyethylene is the most widely-used plastic in the world.
There are two common categories of polyethylene tubing: low density, and high density. Polyethylene tubing is considered to have a low density if it weighs between 0.0814 oz and 0.0839 oz per cubic inch (0.91 and 0.94 grams per cubic centimeter). Low density polyethylene (LDPE) has the advantage of being very flexible and highly resistant to cracks. It is also able to be used in a wide range of temperatures. Many types of it are approved for use with potable water and other food handling applications.
High density polyethylene (HDPE) tubing is defined by a density greater than 0.084 oz per cubic inch (0.941 grams per cubic centimeter). It is not as flexible as LDPE, but it does stand up to sterilization by boiling. This can be an important advantage, especially when it is used for food handling. Tubing made of HDPE also withstands corrosive chemicals better than LDPE, making it the preferred choice for scientific applications.
Polyethylene is a compound which does not occur in nature, and so it must be synthesized in a laboratory or industrial environment. Because of this, its wide use has been limited to the 20th century and beyond. The first person to synthesize polyethylene was the German chemist Hans von Pechmann in 1898. Several more scientists were able to produce it under laboratory conditions over the next few decades. It was not until 1935 that a practical method was invented for producing polyethylene on a larger scale.
Polyethylene as a compound actually has far more uses than just as a component of polyethylene tubing. It is heavily used in numerous consumer products as well, including milk cartons, shopping bags, shrink wrap, and garbage containers, to name a few. Certain types of polyethylene have a very high molecular weight, which results in a very rigid material. It is strong enough for use in bullet-proof vests and butchers’ chopping boards. And yet, it is also chemically inert enough to form parts of the implants used in hip and knee replacements.