polyethyelene

Polyethylene is a polyolefin thermoplastic composed of repeating ethylene units (-CH2-CH2-). It is the most widely produced plastic in the world and exists in several densities and degrees of branching, which determine its mechanical properties and applications. The term polyethylene is sometimes spelled polyethene in British English.

Production and varieties

Polyethylene is formed by polymerizing ethylene monomers. Different processes and catalysts produce distinct types: low-density polyethylene (LDPE) is typically formed under high-pressure, free-radical polymerization that yields a highly branched structure; high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) are produced under lower pressures using Ziegler–Natta or metallocene catalysts, leading to more linear chains and varied branching. Ultra-high-molecular-weight polyethylene (UHMWPE) comprises extremely long chains with exceptional abrasion resistance. These variants fall into a broader family that also includes MDPE and other copolymers, each with specific blend and processing characteristics.

Properties and uses

Polyethylene is chemically inert to water and many chemicals, has good electrical insulation, and exhibits a favorable strength-to-weight ratio. It is relatively inexpensive and easy to process by extrusion, injection molding, blow molding, and film forming. LDPE is prized for flexibility and clarity in films and bags, HDPE for rigid bottles and piping, and LLDPE for film and additional strength. Common applications include packaging films and bags, bottles and containers, tubing and piping, geomembranes, toys, and consumer goods.

Environmental considerations

Polyethylene is durable and resistant to degradation, which contributes to persistence in the environment. Most polyethylene products are recyclable; common codes include HDPE (#2) and LDPE (#4). Recycling, proper waste management, and alternatives to single-use items are important considerations in its lifecycle.

History

Polyethylene was first synthesized in 1933 by chemists at Imperial Chemical Industries (ICI) during high-pressure experiments. It entered commercial production in the mid-20th century, becoming a dominant material in many industries due to its versatility and low cost.

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