Polyethylen

Polyethylene is a polymer consisting of long chains of repeating ethylene units (-CH2-CH2-). It is the simplest and most widely produced plastic, used in a broad range of products from packaging films to piping. It is formed by addition polymerization of ethylene gas, typically under low to moderate pressures with catalysts that control chain length and branching.

Common grades include high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultra-high-molecular-weight polyethylene (UHMWPE). HDPE is more crystalline and has higher density, yielding stiffness and strength; LDPE is highly branched and more flexible. LLDPE combines linear chains with short branches, giving toughness and improved film performance. UHMWPE has extremely long chains, providing exceptional strength and wear resistance and is used in bearing surfaces and medical implants.

Properties of polyethylene are influenced by branching, molecular weight, and copolymerization. It offers good chemical resistance and electrical insulation. HDPE is commonly used for rigid containers, bottles, and pipes; LDPE for flexible films and bags; LLDPE for various film applications; UHMWPE for wear-critical components and medical devices.

Environmental considerations accompany its widespread use. Polyethylene is durable and persistent in the environment, leading to waste management concerns. Recycling is common for HDPE (often coded as plastic code 2) and, to a lesser extent, LDPE (code 4). Mechanical recycling can degrade properties if contamination is not controlled; chemical recycling and energy recovery are areas of ongoing development.

History: Polyethylene was discovered in 1933 by Reginald Gibson and Eric Fawcett at ICI during high-pressure experiments with ethylene. It was first produced commercially in the late 1930s and later expanded rapidly with advances in catalysts and processing.