Polyethylene

Polyethylene is a polyolefin plastic composed of long chains of ethylene monomers (CH2-CH2)n. It is produced by addition polymerization of ethylene, typically using Ziegler-Natta or metallocene catalysts in gas, slurry, or solution processes. The material exists in several densities and molecular weights, reflecting variations in branching and chain length. It is among the most widely used plastics, with widespread consumer and industrial applications.

Common grades include high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultrahigh-molecular-weight polyethylene (UHMWPE). HDPE is relatively stiff with higher crystallinity; LDPE is more flexible due to extensive branching; LLDPE provides improved strength and flexibility at lower density; UHMWPE features very high molecular weight for exceptional toughness and wear resistance. Densities range roughly from 0.91 to 0.97 g/cm3, and melting points vary with grade.

Polyethylene is processed by extrusion, film blowing, injection molding, blow molding, and rotational molding to produce films, bottles, containers, pipes, tapes, and insulation. It is chemically resistant and an effective moisture barrier, with good electrical insulation properties. Additives and copolymers tailor properties for specific applications. Recyclability depends on resin type and contamination; common routes include mechanical recycling into pellets or transformation by chemical recycling.

History: polyethylene was discovered in 1933 by researchers at ICI and later commercialized in the late 1930s. It has since become a dominant material in packaging, construction, and consumer products due to its versatility, low cost, and ease of processing.