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=__**POLYETHYLENE**__=

Polyethylene is a thermoplastic commodity very commonly used in consumer products. It is a polynomer consisting of long chains of monomer ethylene. In the polynomer industry, the name is sometimes shortened to PE. The ethene molecule, C2H4 is CH2=CH2, is two CH2 groups connected by a double bond. Polyethylene is created through polymerization of ethene, like radical polymerization, anionic polymerization, ion coordination polymerization, and cationic addition polymerization. These methods results in different types of polyethylenes.





Polyethylene is classified into multiple different categories based mostly on density and branching. Ultra high molecular weight polyethylene (UHMWPE) is polyethylene with molecular weight in the millions. It's outstanding toughness, cut, wear, and excellent chemical resistance cause it to be used in many different applications, such as can and bottle handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks, and even bulletproof vests.

High density polyethylene (HDPE) is polyethylene with a density greater than or equal to 0.941 g/cm3. It has a low degree of branching with stronger intermolecular forces. It is used in products such as milk jugs, detergent bottles, margarine tubs, garbage containers, and water pipes.

Cross-linked polyethylenes (PEX) are medium-to-high with cross-link bonds in the polynomer structure, making the thermoplast an elastomer. It has high-temperature properties and more chemical resistance, enabling it to be used in materials such as potable water plumbing systems.

Medium-density polyethylene (MDPE) has a medium density range of 0.926–0.940 g/cm3, with good shock and drop resistance properties. It is typically used in gas pipes and fittings, sacks, shrink + packaging film, carrier bags, and screw closures.

Linear low density polyethylene (LLDPE) is defined by a density range of 0.915–0.925 g/cm3. Has high impact and puncture resistance, and also better environmental stress cracking resistance. It is known for it's toughness, flexibility, and transparency. LLDPE is used in packaging, film for bags and sheets, cable covering, toys, lids, buckets/containers, and pipes.

Low density polyethylene (LDPE) is defined by a density range of 0.910–0.940 g/cm3. It has low tensile strength but has good ductility, giving it good, unique flow properties. It is used for rigid containers and plastic film applications (plastic bags and film wrap.)

Very low density polyethylene (VLDPE) is defined by a density range of 0.880–0.915 g/cm3, EXTREMELY low densities. Because of this, VLDPE's are commonly used for hose and tubing, ice and frozen bag foods, and food packaging and stretch wrap.

Other types of polyethylenes include Ultra low molecular weight polyethylene (ULMWPE-PE-WAX), High molecular weight polyethylene (HMWPE), and High density cross-linked polyethylene (HDXLPE).



Hans von Pechmann was the German chemist who first synthesized polyethylene. In 1898 he accidentally prepared it while heating diazomethane, producing the white, waxy substance known as polyethylene. It was not until 1935 that an ICI chemist, Michael Perrin, developed the accidental polyethylene production into a reproducible high-pressure synthesis for polyethylene. This became the basis for industrial LDPE production starting in 1939.

Landmarks in polyethylene synthesis have been centered on the development of multiple different types of catalyst promoting ethylene polymerization at more mild temperatures and pressures. In 1951, Robert Banks J. Paul Hogan discovered the chromium trioxide catalyst of polyethylene. This was called the Phillips Catalyst. In 1953, German chemist Karl Ziegler developed a polyethylene catalytic system based on titanium halides and organoaluminum compounds. This came to be known as the Ziegler Catalyist. In 1976, German Walter Kaminsky developed a third polyethylene catalytic system based on metallocenes.

**References**

 * 1) ** [|^] ** A Guide to IUPAC Nomenclature of Organic Compounds, Blackwell Scientific Publications, Oxford (1993).
 * 2) ^ [|**//a//**] [|**//b//**] J. KAHOVEC, R. B. FOX and K. HATADA; “Nomenclature of regular single-strand organic polymers (IUPAC Recommendations 2002);” Pure and Applied Chemistry; IUPAC; 2002; 74 (10): pp. 1921–1956.
 * 3) ** [|^] ** [|Winnington history in the making]. //This is Cheshire//. Retrieved on [|2006]-[|12-05].