Polyethylene or polythene (abbreviated PE ) is the most common plastic. Its primary use is in packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.).
The properties of polyethylene can be divided into mechanical, chemical, electrical, optical, and thermal properties.
Polyethylene is of low strength, hardness and rigidity, but has a high ductility and impact strength as well as low friction. It shows strong creep under persistent force, which can be reduced by addition of short fibers. It feels waxy when touched.
The usefulness of polyethylene is limited by its melting point of 80 °C (176 °F) (HDPE, types of low crystalline softens earlier). For common commercial grades of medium- and high-density polyethylene the melting point is typically in the range 120 to 180 °C (248 to 356 °F). The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (221 to 239 °F). These temperatures vary strongly with the type of polyethylene.
Polyethylene consists of nonpolar, saturated, high molecular weight hydrocarbons.Because of their symmetric molecular structure, they tend to crystallize; overall polyethylene is partially crystalline. Higher crystallinity increases density and mechanical and chemical stability.
Most LDPE, MDPE, and HDPE grades have excellent chemical resistance, meaning they are not attacked by strong acids or strong bases, and are resistant to gentle oxidants and reducing agents. Crystalline samples do not dissolve at room temperature.
Polyethylene absorbs almost no water. The gas and water vapor permeability (only polar gases) is lower than for most plastics; oxygen, carbon dioxide and flavorings on the other hand can pass it easily.
PE can become brittle when exposed to sunlight, carbon black is usually used as a UV stabilizer.
Polyethylene cannot be imprinted or stuck together without pretreatment.
Polyethylene is a good electrical insulator. It offers good tracking resistance.
Depending on thermal history and film thickness PE can vary between almost clear (transparent), milky-opaque (translucent) or opaque. LDPE thereby owns the greatest, LLDPE slightly less and HDPE the least transparency. Transparency is reduced by crystallites if they are larger than the wavelength of visible light.