polietylen

Polietylen, also known as polyethylene, is a polymer formed from the simple hydrocarbon ethylene (ethene) monomers. Its repeating unit is −CH2−CH2−, and it is produced by addition polymerization without the generation of small molecule byproducts. It is the most widely produced plastic in the world and comes in several densities and forms that determine its properties and applications.

Polyetylene can be produced under different conditions to give distinct types. High-pressure processes yield low-density polyethylene (LDPE), which has a branched structure and is flexible. Low-pressure, catalytic processes produce high-density polyethylene (HDPE) with a more crystalline structure and greater stiffness. Linear low-density polyethylene (LLDPE) is produced by copolymerizing ethylene with short-chain α-olefins, combining some flexibility with higher strength.

Historically, polyethylene was first produced in 1933 by Reginald Gibson and Eric Fawcett at Imperial Chemical Industries (ICI) during high-pressure polymerization. Its commercial significance grew with the development of Ziegler–Natta and later metallocene catalysts in the 1950s and beyond, enabling more controlled polymer structures and new applications.

Key properties of polyethylene include its thermoplastic nature, chemical resistance, electrical insulation, and relatively low cost. Mechanical properties vary with density: HDPE is stiff and strong, LDPE is more ductile and transparent, and LLDPE offers a balance of toughness and flexibility. These materials are widely used in packaging films, bags, bottles, pipes, geomembranes, and consumer goods.

Recycling and environmental aspects are important considerations. Polyethylene is widely recycled, with common codes including HDPE (recycling code #2) and LDPE (code #4); challenges remain related to persistence and waste management in single-use applications.