Polyethylene
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Polyethylene or polythene (abbreviated PE;
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
name polyethene or poly(methylene)) is the most commonly produced
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
. It is a
polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
, primarily used for
packaging Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a coo ...
(
plastic bag A plastic bag, poly bag, or pouch is a type of container made of thin, flexible, plastic film, nonwoven fabric, or plastic textile. Plastic bags are used for containing and transporting goods such as foods, produce, Powder (substance), powders, ...
s,
plastic film Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a "sheet". These thin plastic membranes are used to separate areas or volumes, to hold items, to act as barriers, or as printable surfaces. Plast ...
s,
geomembranes A geomembrane is very low permeability (earth sciences), permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, ...
and containers including
bottle A bottle is a narrow-necked container made of an impermeable material (such as glass, plastic or aluminium) in various shapes and sizes that stores and transports liquids. Its mouth, at the bottling line, can be sealed with an internal ...
s,
cup A cup is an open-top vessel (container) used to hold liquids for drinking, typically with a flattened hemispherical shape, and often with a capacity of about . Cups may be made of pottery (including porcelain), glass, metal, wood, stone, pol ...
s, jars, etc.). , over 100 million
tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1,000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...
s of polyethylene
resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...
s are being produced annually, accounting for 34% of the total plastics market. Many kinds of polyethylene are known, with most having the
chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...
(C2H4)''n''. PE is usually a mixture of similar
polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
s of
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...
, with various values of ''n''. It can be ''low-density'' or ''high-density'' and many variations thereof. Its properties can be modified further by crosslinking or copolymerization. All forms are nontoxic as well as chemically resilient, contributing to polyethylene's popularity as a multi-use plastic. However, polyethylene's chemical resilience also makes it a long-lived and decomposition-resistant pollutant when disposed of improperly. Being a
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
, polyethylene is colorless to opaque (without impurities or colorants) and combustible.


History

Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while investigating
diazomethane Diazomethane is an organic chemical compound with the formula CH2N2, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow ga ...
. When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy substance that he had created, they recognized that it contained long −CH2− chains and termed it ''polymethylene''. The first industrially practical polyethylene synthesis (diazomethane is a notoriously unstable substance that is generally avoided in industrial syntheses) was again accidentally discovered in 1933 by Eric Fawcett and Reginald Gibson at the
Imperial Chemical Industries Imperial Chemical Industries (ICI) was a British Chemical industry, chemical company. It was, for much of its history, the largest manufacturer in Britain. Its headquarters were at Millbank in London. ICI was listed on the London Stock Exchange ...
(ICI) works in
Northwich Northwich is a market town and civil parish in the Cheshire West and Chester borough of Cheshire, England. It lies on the Cheshire Plain, at the confluence of the rivers Weaver and Dane, east of Chester, south of Warrington and south of Ma ...
,
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
. Upon applying extremely high pressure (several hundred atmospheres) to a mixture of ethylene and
benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is among the simplest aromatic aldehydes and one of the most industrially useful. It is a colorless liquid with a characteristic almond-li ...
they again produced a white, waxy material. Because the reaction had been initiated by trace
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
contamination in their apparatus, the experiment was difficult to reproduce at first. It was not until 1935 that another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial low-density polyethylene ( LDPE) production beginning in 1939. Because polyethylene was found to have very low-loss properties at very high frequency radio waves, commercial distribution in Britain was suspended on the outbreak of World War II, secrecy imposed, and the new process was used to produce insulation for UHF and SHF
coaxial cable Coaxial cable, or coax (pronounced ), is a type of electrical cable consisting of an inner Electrical conductor, conductor surrounded by a concentric conducting Electromagnetic shielding, shield, with the two separated by a dielectric (Insulat ...
s of
radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...
sets. During World War II, further research was done on the ICI process and in 1944,
DuPont Dupont, DuPont, Du Pont, duPont, or du Pont may refer to: People * Dupont (surname) Dupont, also spelled as DuPont, duPont, Du Pont, or du Pont is a French surname meaning "of the bridge", historically indicating that the holder of the surname re ...
at Sabine River, Texas, and
Union Carbide Corporation Union Carbide Corporation (UCC) is an American chemical company headquartered in Seadrift, Texas. It has been a wholly owned subsidiary of Dow Chemical Company since 2001. Union Carbide produces chemicals and polymers that undergo one or more f ...
at South Charleston, West Virginia, began large-scale commercial production under license from ICI. The landmark breakthrough in the commercial production of polyethylene began with the development of
catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
s that promoted the
polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
at mild temperatures and pressures. The first of these was a catalyst based on
chromium trioxide Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula . It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid ...
discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum. In 1953 the German chemist Karl Ziegler developed a catalytic system based on
titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
halides and organoaluminium compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are heavily used industrially. By the end of the 1950s both the Phillips- and Ziegler-type catalysts were being used for high-density polyethylene (HDPE) production. In the 1970s, the Ziegler system was improved by the incorporation of
magnesium chloride Magnesium chloride is an inorganic compound with the formula . It forms hydrates , where ''n'' can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which ...
. Catalytic systems based on soluble catalysts, the metallocenes, were reported in 1976 by Walter Kaminsky and Hansjörg Sinn. The Ziegler- and metallocene-based catalysts families have proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene
resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...
s available today, including very-low-density polyethylene and linear low-density polyethylene. Such resins, in the form of UHMWPE fibers, have (as of 2005) begun to replace
aramid Aramid fibers, short for aromatic polyamide, are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic-rated bulletproof vest, body armor cloth, fabric and ballistic composites ...
s in many high-strength applications.


Properties

The properties of polyethylene depend strongly on type. The molecular weight, crosslinking, and presence of comonomers all strongly affect its properties. It is for this structure-property relation that intense effort has been invested into diverse kinds of PE. LDPE is softer and more transparent than HDPE. For medium- and high-density polyethylene the melting point is typically in the range . The melting point for average commercial low-density polyethylene is typically . These temperatures vary strongly with the type of polyethylene, but the theoretical upper limit of melting of polyethylene is reported to be . Combustion typically occurs above . Most LDPE, MDPE, and HDPE grades have excellent chemical resistance, meaning that they are not attacked by strong acids or strong bases and are resistant to gentle oxidants and reducing agents. Crystalline samples do not dissolve at room temperature. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in
aromatic hydrocarbon Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...
s such as
toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...
or xylene, or in chlorinated solvents such as trichloroethane or trichlorobenzene. Polyethylene absorbs almost no
water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
. The permeability for water vapor and polar gases of is lower than for most plastics. On the other hand, non-polar gases such as
Oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
,
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
, and flavorings can pass it easily. Polyethylene burns slowly with a blue flame having a yellow tip and gives off an odour of paraffin (similar to
candle A candle is an ignitable candle wick, wick embedded in wax, or another flammable solid substance such as tallow, that provides light, and in some cases, a Aroma compound, fragrance. A candle can also provide heat or a method of keeping time. ...
flame). The material continues burning on removal of the flame source and produces a drip. Polyethylene cannot be imprinted or bonded with adhesives without pretreatment. High-strength joints are readily achieved with plastic welding.


Electrical

Polyethylene is a good
electrical insulator An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and electrical conductor, conductors—con ...
. It offers good electrical treeing resistance; however, it becomes easily electrostatically charged (which can be reduced by additions of
graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...
,
carbon black Carbon black (with subtypes acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of coal tar, vegetable matter, or petroleum products, including fuel oil, fluid cataly ...
or
antistatic agent An antistatic agent is a compound used for treatment of materials or their surfaces in order to reduce or eliminate buildup of static electricity. Static charge may be generated by the triboelectric effect or by a non-contact process using a high ...
s). When pure, the
dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insul ...
is in the range 2.2 to 2.4 depending on the density and the loss tangent is very low, making it a good dielectric for building
capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
s. For the same reason it is commonly used as the insulation material for high-frequency coaxial and twisted pair cables.


Optical

Depending on thermal history and film thickness, PE can vary between almost clear ( transparent), milky-opaque (
translucent In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable light scattering by particles, scattering of light. On a macroscopic scale ...
) and opaque. LDPE has the greatest, LLDPE slightly less, and HDPE the least transparency. Transparency is reduced by
crystallite A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains. Bacillite is a type of crystallite. It is rodlike with parallel Wikt:longulite ...
s if they are larger than the wavelength of visible light.


Manufacturing process


Monomer

The ingredient or
monomer A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization. Classification Chemis ...
is
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...
(
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
name ethene), a gaseous
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
with the formula C2H4, which can be viewed as a pair of methylene groups (−−) connected to each other. Typical specifications for PE purity are <5 ppm for water, oxygen, and other
alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...
s contents. Acceptable contaminants include N2, ethane (common precursor to ethylene), and methane. Ethylene is usually produced from petrochemical sources, but is also generated by dehydration of ethanol.


Polymerization

Polymerization of ethylene to polyethylene is described by the following
chemical equation A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the Product (chemistry), product entities are on the right-hand side ...
: : (gas) → − (solid) Δ/ =  Ethylene is a stable molecule that polymerizes only upon contact with catalysts. The conversion is highly
exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...
. Coordination polymerization is the most pervasive technology, which means that metal chlorides or metal oxides are used. The most common catalysts consist of
titanium(III) chloride Titanium(III) chloride is the inorganic compound with the formula TiCl3. At least four distinct species have this formula; additionally hydrated derivatives are known. TiCl3 is one of the most common halides of titanium and is an important cataly ...
, the so-called
Ziegler–Natta catalyst A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes ( alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility ...
s. Another common catalyst is the Phillips catalyst, prepared by depositing chromium(VI) oxide on silica. Polyethylene can be produced through radical polymerization, but this route has only limited utility and typically requires high-pressure apparatus.


Joining

Commonly used methods for joining polyethylene parts together include:Plastics Design Library (1997). ''Handbook of Plastics Joining: A Practical Guide''. Norwich, New York: Plastics Design Library. p. 326. . *
Welding Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melting, melt the parts together and allow them to cool, causing Fusion welding, fusion. Co ...
** Hot gas welding ** Infrared welding ** Laser welding ** Ultrasonic welding ** Heat sealing ** Heat fusion *
Fastening A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...
*
Adhesives Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantage ...
**
Pressure-sensitive adhesive Pressure-sensitive adhesive (PSA, self-adhesive, self-stick adhesive) is a type of nonreactive adhesive which forms a bond when pressure is applied to bond the adhesive with a surface. No solvent, water, or heat is needed to activate the adhesive ...
(PSAs) *** Dispersion of solvent-type PSAs **
Polyurethane Polyurethane (; often abbreviated PUR and PU) is a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane term ...
contact adhesives ** Two-part polyurethane ** Epoxy adhesives **
Hot-melt adhesive Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating el ...
s ** Solvent bonding
Adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantage ...
s and
solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
s are rarely used as solvent bonding because polyethylene is
nonpolar In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain one or more polar ...
and has a high resistance to solvents.
Pressure-sensitive adhesive Pressure-sensitive adhesive (PSA, self-adhesive, self-stick adhesive) is a type of nonreactive adhesive which forms a bond when pressure is applied to bond the adhesive with a surface. No solvent, water, or heat is needed to activate the adhesive ...
s (PSA) are feasible if the surface chemistry or charge is modified with
plasma activation Plasma activation (or plasma functionalization) is a method of surface functionalization, surface modification employing plasma processing, which improves surface adhesion properties of many materials including metals, glass, ceramics, a broad rang ...
, flame treatment, or
corona treatment Corona treatment (sometimes referred to as air plasma) is a surface modification technique that uses a low temperature corona discharge plasma to impart changes in the properties of a surface. The corona plasma is generated by the application ...
.


Classification

Polyethylene is classified by its
density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
and branching. Its mechanical properties depend significantly on variables such as the extent and type of branching, the crystal structure, and the
molecular weight A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
. There are several types of polyethylene: *
Ultra-high-molecular-weight polyethylene Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a subset of the thermoplastic polyethylene. Also known as high-modulus polyethylene (HMPE), it has extremely long chains, with a molecular mass typically between 2 and 6 million amu. The l ...
(UHMWPE) *Ultra-low-molecular-weight polyethylene (ULMWPE or PE-WAX) *High-molecular-weight polyethylene (HMWPE) *
High-density polyethylene High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or " polythene" when used for HDPE pipes. With a high strength-to-density rati ...
(HDPE) *High-density cross-linked polyethylene (HDXLPE) *
Cross-linked polyethylene Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, in ...
(PEX or XLPE) * Medium-density polyethylene (MDPE) * Linear low-density polyethylene (LLDPE) * Low-density polyethylene (LDPE) *Very-low-density polyethylene (VLDPE) * Chlorinated polyethylene (CPE) With regard to sold volumes, the most important polyethylene grades are HDPE, LLDPE, and LDPE.


Ultra-high-molecular-weight (UHMWPE)

UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.5 and 7.5 million amu. The high molecular weight makes it a very tough material, but results in less efficient packing of the chains into the
crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...
as evidenced by densities of less than high-density polyethylene (for example, 0.930–0.935 g/cm3). UHMWPE can be made through any catalyst technology, although Ziegler catalysts are most common. Because of its outstanding toughness and its cut, wear, and excellent chemical resistance, UHMWPE is used in a diverse range of applications. These include can- and
bottle A bottle is a narrow-necked container made of an impermeable material (such as glass, plastic or aluminium) in various shapes and sizes that stores and transports liquids. Its mouth, at the bottling line, can be sealed with an internal ...
-handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks, steel cable replacements on ships, and butchers' chopping boards. It is commonly used for the construction of articular portions of implants used for hip and
knee replacement Knee replacement, also known as knee arthroplasty, is a surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve pain and disability, most commonly offered when joint pain is not diminished by conservative sources. ...
s. As
fiber Fiber (spelled fibre in British English; from ) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often inco ...
, it competes with
aramid Aramid fibers, short for aromatic polyamide, are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic-rated bulletproof vest, body armor cloth, fabric and ballistic composites ...
in bulletproof vests.


High-density (HDPE)

HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching. The mostly linear molecules pack together well, so intermolecular forces are stronger than in highly branched polymers. HDPE can be produced by
chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...
/silica catalysts,
Ziegler–Natta catalyst A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes ( alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility ...
s or metallocene catalysts; by choosing catalysts and reaction conditions, the small amount of branching that does occur can be controlled. These catalysts prefer the formation of
free radicals In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired electron, unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemical reaction, chemi ...
at the ends of the growing polyethylene molecules. They cause new ethylene monomers to add to the ends of the molecules, rather than along the middle, causing the growth of a linear chain. HDPE has high tensile strength. It is used in products and packaging such as milk jugs, detergent bottles, butter tubs, garbage containers, and water pipes.


Cross-linked (PEX or XLPE)

PEX is a medium- to high-density polyethylene containing
cross-link In chemistry and biology, a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
bonds introduced into the polymer structure, changing the thermoplastic into a
thermoset In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and ...
. The high-temperature properties of the polymer are improved, its flow is reduced, and its chemical resistance is enhanced. PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight connection.


Medium-density (MDPE)

MDPE is defined by a density range of 0.926–0.940 g/cm3. MDPE can be produced by chromium/silica catalysts, Ziegler–Natta catalysts, or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch-sensitive than HDPE; stress-cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags, and screw closures.


Linear low-density (LLDPE)

LLDPE is defined by a density range of 0.915–0.925 g/cm3. LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain
alpha-olefin In organic chemistry, terminal alkenes (alpha-olefins, α-olefins, or 1-alkenes) are a family of organic compounds which are alkenes (also known as olefins) with a chemical formula , distinguished by having a double bond at the primary, Alpha an ...
s (for example,
1-butene 1-Butene (IUPAC name: But-1-ene, also known as 1-butylene) is the organic compound with the formula CH3CH2CH=CH2. It is a colorless gas, but easily condensed to give a colorless liquid. It is classified as a linear alpha-olefin (terminal alkene). ...
, 1-hexene, and 1-octene). LLDPE has higher tensile strength than LDPE, and it exhibits higher impact and puncture resistance than LDPE. Lower-thickness (gauge) films can be blown, compared with LDPE, with better environmental stress cracking resistance, but they are not as easy to process. LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. It is used for cable coverings, toys, lids, buckets, containers, and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility, and relative transparency. Product examples range from agricultural films, Saran wrap, and bubble wrap to multilayer and composite films.


Low-density (LDPE)

LDPE is defined by a density range of 0.910–0.940 g/cm3. LDPE has a high degree of short- and long-chain branching, which means that the chains do not pack into the
crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...
as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower
tensile strength Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
and increased
ductility Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...
. LDPE is created by free-radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap. The radical polymerization process used to make LDPE does not include a catalyst that "supervises" the radical sites on the growing PE chains. (In HDPE synthesis, the radical sites are at the ends of the PE chains, because the catalyst stabilizes their formation at the ends.) Secondary radicals (in the middle of a chain) are more stable than primary radicals (at the end of the chain), and tertiary radicals (at a branch point) are more stable yet. Each time an ethylene monomer is added, it creates a primary radical, but often these will rearrange to form more stable secondary or tertiary radicals. Addition of ethylene monomers to the secondary or tertiary sites creates branching.


Very-low-density (VLDPE)

VLDPE is defined by a density range of 0.880–0.915 g/cm3. VLDPE is a substantially linear polymer with high levels of short-chain branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). VLDPE is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts. VLDPEs are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap as well as impact modifiers when blended with other polymers. Much research activity has focused on the nature and distribution of long chain branches in polyethylene. In HDPE, a relatively small number of these branches, perhaps one in 100 or 1,000 branches per backbone carbon, can significantly affect the rheological properties of the polymer.


Copolymers

In addition to copolymerization with alpha-olefins, ethylene can be copolymerized with a wide range of other monomers and ionic composition that creates ionized free radicals. Common examples include
vinyl acetate Vinyl acetate is an organic compound with the Chemical formula, formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, and other important industrial polymers. Prod ...
(the resulting product is
ethylene-vinyl acetate Ethylene-vinyl acetate (EVA), also known as poly(ethylene-vinyl acetate) (PEVA), is a copolymer of ethylene and vinyl acetate. The weight percent of vinyl acetate usually varies from 10 to 50%, with the remainder being ethylene. There are three ...
copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...
, or EVA, widely used in athletic-shoe sole foams) and a variety of
acrylate Acrylates (IUPAC: prop-2-enoates) are the salts, esters, and conjugate bases of acrylic acid. The acrylate ion is the anion . Often, acrylate refers to esters of acrylic acid, the most common member being methyl acrylate. These acrylates contain ...
s. Applications of acrylic copolymer include packaging and sporting goods, and superplasticizer, used in cement production.


Types of polyethylenes

The particular material properties of "polyethylene" depend on its molecular structure. Molecular weight and crystallinity are the most significant factors; crystallinity in turn depends on molecular weight and degree of branching. The less the polymer chains are branched, and the lower the molecular weight, the higher the crystallinity of polyethylene. Crystallinity ranges from 35% (PE-LD/PE-LLD) to 80% (PE-HD). Polyethylene has a density of 1.0 g/cm3 in crystalline regions and 0.86 g/cm3 in amorphous regions. An almost linear relationship exists between density and crystallinity. The degree of branching of the different types of polyethylene can be schematically represented as follows: The figure shows polyethylene backbones, short-chain branches and side-chain branches. The polymer chains are represented linearly.


Chain branches

The properties of polyethylene are highly dependent on type and number of chain branches. The chain branches in turn depend on the process used: either the high-pressure process (only PE-LD) or the low-pressure process (all other PE grades). Low-density polyethylene is produced by the high-pressure process by radical polymerization, thereby numerous short chain branches as well as long chain branches are formed. Short chain branches are formed by intramolecular
chain transfer In polymer chemistry, chain transfer is a polymerization reaction by which the activity of a growing polymer chain is transferred to another molecule: \ce^\bullet + \ce^\bullet where • is the active center, P is the initial polymer chain, X i ...
reactions, they are always butyl or ethyl chain branches because the reaction proceeds after the following mechanism: :


Environmental issues

The widespread usage of polyethylene poses potential difficulties for
waste management Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment, and disposal of waste, together with monitor ...
because it is not readily biodegradable. Since 2008, Japan has increased plastic recycling, but still has a large amount of plastic wrapping which goes to waste. Plastic recycling in Japan is a potential US$90
billion Billion is a word for a large number, and it has two distinct definitions: * 1,000,000,000, i.e. one thousand million, or (ten to the ninth power), as defined on the short scale. This is now the most common sense of the word in all varieties of ...
market. It is possible to rapidly convert polyethylene to hydrogen and
graphene Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ...
by heating. The energy needed is much less than for producing hydrogen by electrolysis.


Biodegradability

Several experiments have been conducted aimed at discovering
enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
or organisms that will degrade polyethylene. Several plastics - polyesters, polycarbonates, polyamides - degrade either by hydrolysis or air oxidation. In some cases the degradation is increased by bacteria or various enzyme cocktails. The situation is very different with polymers where the backbone consists solely of C-C bonds. These polymers include polyethylene, but also polypropylene, polystyrene and acrylates. At best, these polymers degrade very slowly, but these experiments are difficult because yields and rates are very slow. Further confusing the situation, even preliminary successes are greeted with enthusiasm by the popular press. Some technical challenges in this area include the failure to identify enzymes responsible for the proposed degradation. Another issue is that organisms are incapable of importing hydrocarbons of molecular weight greater than 500.


Bacteria and insect case studies

The Indian mealmoth larvae are claimed to metabolize polyethylene based on observing that plastic bags at a researcher's home had small holes in them. Deducing that the hungry larvae must have digested the plastic somehow, he and his team analyzed their gut bacteria and found a few that could use plastic as their only carbon source. Not only could the bacteria from the guts of the ''Plodia interpunctella'' moth larvae metabolize polyethylene, they degraded it significantly, dropping its tensile strength by 50%, its mass by 10% and the molecular weights of its polymeric chains by 13%. The caterpillar of '' Galleria mellonella'' is claimed to consume polyethylene. The caterpillar is able to digest polyethylene due to a combination of its
gut microbiota Gut microbiota, gut microbiome, or gut flora are the microorganisms, including bacteria, archaea, fungi, and viruses, that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the g ...
and its saliva containing
enzymes An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...
that oxidise and depolymerise the plastic.


Climate change

When exposed to ambient solar radiation the plastic produces trace amounts of two
greenhouse gas Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...
es,
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
and
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...
. The plastic type which releases gases at the highest rate is low-density polyethylene (LDPE). Due to its low density it breaks down more easily over time, leading to higher surface areas. When incubated in air, LDPE emits gases at rates ~2 times and ~76 times higher in comparison to incubation in water for methane and ethylene, respectively. However, based on the rates measured in the study methane production by plastics is presently an insignificant component of the global methane budget.


Chemically modified polyethylene

Polyethylene may either be modified in the polymerization by polar or non-polar
comonomer In polymer chemistry, a comonomer refers to a polymerizable precursor to a copolymer aside from the principal monomer. In some cases, only small amounts of a comonomer are employed, in other cases substantial amounts of comonomers are used. Furt ...
s or after polymerization through polymer-analogous reactions. Common polymer-analogous reactions are in case of polyethylene crosslinking, chlorination and sulfochlorination.


Non-polar ethylene copolymers


α-olefins

In the low pressure process α-olefins (e.g.
1-butene 1-Butene (IUPAC name: But-1-ene, also known as 1-butylene) is the organic compound with the formula CH3CH2CH=CH2. It is a colorless gas, but easily condensed to give a colorless liquid. It is classified as a linear alpha-olefin (terminal alkene). ...
or 1-hexene) may be added, which are incorporated in the polymer chain during polymerization. These copolymers introduce short side chains, thus crystallinity and
density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
are reduced. As explained above, mechanical and thermal properties are changed thereby. In particular, PE-LLD is produced this way.


Metallocene polyethylene (PE-MC)

Metallocene polyethylene (PE-M) is prepared by means of metallocene catalysts, usually including copolymers (z. B. ethene / hexene). Metallocene polyethylene has a relatively narrow molecular weight distribution, exceptionally high toughness, excellent optical properties and a uniform comonomer content. Because of the narrow molecular weight distribution it behaves less pseudoplastic (especially under larger shear rates). Metallocene polyethylene has a low proportion of low molecular weight (extractable) components and a low welding and sealing temperature. Thus, it is particularly suitable for the food industry.


Polyethylene with multimodal molecular weight distribution

Polyethylene with multimodal molecular weight distribution consists of several polymer fractions, which are homogeneously mixed. Such polyethylene types offer extremely high stiffness, toughness, strength, stress crack resistance and an increased crack propagation resistance. They consist of equal proportions higher and lower molecular polymer fractions. The lower molecular weight units crystallize easier and relax faster. The higher molecular weight fractions form linking molecules between crystallites, thereby increasing toughness and stress crack resistance. Polyethylene with multimodal molecular weight distribution can be prepared either in two-stage reactors, by catalysts with two active centers on a carrier or by blending in extruders.


Cyclic olefin copolymers (COC)

Cyclic olefin copolymers are prepared by copolymerization of ethene and cycloolefins (usually norbornene) produced by using metallocene catalysts. The resulting polymers are amorphous polymers and particularly transparent and heat resistant.


Polar ethylene copolymers

The basic compounds used as polar comonomers are vinyl alcohol ( Ethenol, an unsaturated alcohol), acrylic acid ( propenoic acid, an unsaturated acid) and
ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s containing one of the two compounds.


Ethylene copolymers with unsaturated alcohols

Ethylene/vinyl alcohol copolymer (EVOH) is (formally) a copolymer of PE and vinyl alcohol (ethenol), which is prepared by (partial) hydrolysis of ethylene-vinyl acetate copolymer (as vinyl alcohol itself is not stable). However, typically EVOH has a higher comonomer content than the VAC commonly used. EVOH is used in multilayer films for packaging as a barrier layer (barrier plastic). As EVOH is hygroscopic (water-attracting), it absorbs water from the environment, whereby it loses its barrier effect. Therefore, it must be used as a core layer surrounded by other plastics (like LDPE, PP, PA or PET). EVOH is also used as a coating agent against corrosion at street lights, traffic light poles and noise protection walls.


Ethylene/acrylic acid copolymers (EAA)

Copolymer of ethylene and unsaturated carboxylic acids (such as acrylic acid) are characterized by good adhesion to diverse materials, by resistance to stress cracking and high flexibility. However, they are more sensitive to heat and oxidation than ethylene homopolymers. Ethylene/acrylic acid copolymers are used as adhesion promoters. If salts of an unsaturated carboxylic acid are present in the polymer, thermo-reversible ion networks are formed, they are called ionomers. Ionomers are highly transparent thermoplastics which are characterized by high adhesion to metals, high abrasion resistance and high water absorption.


Ethylene copolymers with unsaturated esters

If unsaturated esters are copolymerized with ethylene, either the alcohol moiety may be in the polymer backbone (as it is the case in ethylene-vinyl acetate copolymer) or of the acid moiety (e. g. in ethylene-ethyl acrylate copolymer).
Ethylene-vinyl acetate Ethylene-vinyl acetate (EVA), also known as poly(ethylene-vinyl acetate) (PEVA), is a copolymer of ethylene and vinyl acetate. The weight percent of vinyl acetate usually varies from 10 to 50%, with the remainder being ethylene. There are three ...
copolymers are prepared similarly to LD-PE by high pressure polymerization. The proportion of comonomer has a decisive influence on the behaviour of the polymer. The density decreases up to a comonomer share of 10% because of the disturbed crystal formation. With higher proportions it approaches to the one of polyvinyl acetate (1.17 g/cm3). Due to decreasing crystallinity ethylene vinyl acetate copolymers are getting softer with increasing comonomer content. The polar side groups change the chemical properties significantly (compared to polyethylene): weather resistance, adhesiveness and weldability rise with comonomer content, while the chemical resistance decreases. Also mechanical properties are changed: stress cracking resistance and toughness in the cold rise, whereas yield stress and heat resistance decrease. With a very high proportion of comonomers (about 50%) rubbery thermoplastics are produced (
thermoplastic elastomer Thermoplastic elastomers (TPE), sometimes referred to as thermoplastic rubbers (TPR), are a class of copolymers or a physical mix of polymers (usually a plastic and a rubber) that consist of materials with both thermoplastic and elastomeric prop ...
s). Ethylene-ethyl acrylate copolymers behave similarly to ethylene-vinyl acetate copolymers.


Crosslinking

A basic distinction is made between peroxide crosslinking (PE-Xa), silane crosslinking (PE-Xb), electron beam crosslinking (PE-Xc) and azo crosslinking (PE-Xd).Vorschau auf kunststoffe.de
/ref> Shown are the peroxide, the silane and irradiation crosslinking. In each method, a radical is generated in the polyethylene chain (top center), either by radiation (h·ν) or by peroxides (R-O-O-R). Then, two radical chains can either directly crosslink (bottom left) or indirectly by silane compounds (bottom right). *Peroxide crosslinking (PE-Xa): The crosslinking of polyethylene using
peroxide In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...
s (e. g. dicumyl or di-tert-butyl peroxide) is still of major importance. In the so-called ''Engel process'', a mixture of HDPE and 2% peroxide is at first mixed at low temperatures in an extruder and then crosslinked at high temperatures (between 200 and 250 °C). The peroxide decomposes to peroxide radicals (RO•), which abstract (remove) hydrogen atoms from the polymer chain, leading to radicals. When these combine, a crosslinked network is formed. The resulting polymer network is uniform, of low tension and high flexibility, whereby it is softer and tougher than (the irradiated) PE-Xc. *Silane crosslinking (PE-Xb): In the presence of silanes (e.g. trimethoxyvinylsilane) polyethylene can initially be Si- functionalized by irradiation or by a small amount of a peroxide. Later Si-OH groups can be formed in a water bath by
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
, which condense then and crosslink the PE by the formation of Si-O-Si bridges. 6
Catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
s such as dibutyltin dilaurate may accelerate the reaction. *Irradiation crosslinking (PE-Xc): The crosslinking of polyethylene is also possible by a downstream radiation source (usually an electron accelerator, occasionally an isotopic radiator). PE products are crosslinked below the crystalline melting point by splitting off
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
atoms. β-radiation possesses a
penetration depth Penetration depth is a measure of how deep light or any electromagnetic radiation can penetrate into a material. It is defined as the depth at which the intensity of the radiation inside the material falls to 1/ ''e'' (about 37%) of its original ...
of 10 mm, ɣ-radiation 100 mm. Thereby the interior or specific areas can be excluded from the crosslinking. However, due to high capital and operating costs radiation crosslinking plays only a minor role compared with the peroxide crosslinking. In contrast to peroxide crosslinking, the process is carried out in the solid state. Thereby, the cross-linking takes place primarily in the amorphous regions, while the crystallinity remains largely intact. *Azo crosslinking (PE-Xd): In the so-called ''Lubonyl process'' polyethylene is crosslinked preadded
azo compound Azo compounds are organic compounds bearing the functional group diazenyl (, in which R and R′ can be either aryl or alkyl groups). IUPAC defines azo compounds as: "Derivatives of diazene (diimide), , wherein both hydrogens are substituted ...
s after extrusion in a hot salt bath.


Chlorination and sulfochlorination

Chlorinated Polyethylene (PE-C) is an inexpensive material having a chlorine content from 34 to 44%. It is used in blends with PVC because the soft, rubbery chloropolyethylene is embedded in the PVC matrix, thereby increasing the
impact resistance In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing. When chlorinated polyethylene is added to other polyolefins, it reduces the flammability. Chlorosulfonated PE (CSM) is used as starting material for ozone-resistant
synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About of rubber is produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubber, just like natural ru ...
.


Bio-based polyethylene

Braskem and Toyota Tsusho Corporation started joint marketing activities to produce polyethylene from
sugarcane Sugarcane or sugar cane is a species of tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fib ...
. Braskem will build a new facility at their existing industrial unit in Triunfo, Rio Grande do Sul, Brazil with an annual production capacity of , and will produce high-density and low-density polyethylene from bioethanol derived from sugarcane.


Nomenclature and general description of the process

The name polyethylene comes from the ingredient and not the resulting chemical compound, which contains no double bonds. The scientific name ''polyethene'' is systematically derived from the scientific name of the monomer. The alkene monomer converts to a long, sometimes ''very'' long, alkane in the polymerization process. In certain circumstances it is useful to use a structure-based nomenclature; in such cases
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
recommends poly(methylene) (poly(methanediyl) is a non-preferred alternative). The difference in names between the two systems is due to the ''opening up'' of the monomer's double bond upon polymerization. The name is abbreviated to ''PE''. In a similar manner
polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefin ...
and
polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It i ...
are shortened to PP and PS, respectively. In the United Kingdom and India the polymer is commonly called ''polythene'', from the ICI
trade name A trade name, trading name, or business name is a pseudonym used by companies that do not operate under their registered company name. The term for this type of alternative name is fictitious business name. Registering the fictitious name with ...
, although this is not recognized scientifically.


Footnotes


References


Bibliography

* *


External links


Polythene's story: The accidental birth of plastic bags
Kawawada, Karen, ''Waterloo Region Record'' (22 May 2008). {{Authority control Polyolefins Dielectrics Ethylene Thermoplastics Packaging materials Transparent materials Bioplastics Commodity chemicals German inventions 1898 in science 1898 in Germany