Polyethylene or polythene (IUPAC The International Union of Pure and Applied Chemistry , pronounced /ˈaɪjuːpæk/, is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science (ICSU). The international headquarters of IUPAC is located in Zürich, Switzerland. The name polyethene or poly(methylene)) is the most widely used plastic A plastic material is any of a wide range of synthetic or semi-synthetic organic amorphous solids[citation needed] used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce costs. Monomers of plastic are either natural or synthetic, with an annual production of approximately 80 million metric tons.[1] Its primary use is within packaging (notably the plastic shopping bag Plastic shopping bags, carrier bags or plastic grocery bags are a common type of shopping bag in several countries. Most often these bags are intended for a single use to carry items from a store to a home: reuse for storage or trash is common. Heavier duty plastic shopping bags are suitable for multiple uses as reusable shopping bags).

Contents

Description

Polyethylene is a thermoplastic A thermoplastic, also known as thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces ; stronger dipole-dipole interactions and hydrogen bonding (nylon); or polymer A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties consisting of long chains of the monomer A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer. The most common natural monomer is glucose, which is linked by glycosidic bonds into polymers such as cellulose and starch, and is over 76% of the weight of all plant matter. Most often the term monomer refers to the organic molecules which form ethylene Ethylene is a gaseous organic compound with the formula C2H4. It is the simplest alkene (older name: olefin from its oil-forming property). Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and also has a role in biology as a hormone. Ethylene is the most (IUPAC The International Union of Pure and Applied Chemistry , pronounced /ˈaɪjuːpæk/, is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science (ICSU). The international headquarters of IUPAC is located in Zürich, Switzerland. The name ethene). The recommended scientific name polyethene is systematically derived from the scientific name of the monomer.[2][3] In certain circumstances it is useful to use a structure-based nomenclature; in such cases IUPAC The International Union of Pure and Applied Chemistry , pronounced /ˈaɪjuːpæk/, is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science (ICSU). The international headquarters of IUPAC is located in Zürich, Switzerland. The recommends poly(methylene)[3] (poly(methanediyl) is an non-preferred alternative[4][5]). 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 manner similar to that by which other polymers like polypropylene Polypropylene , also known as polypropene, is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polystyrene Polystyrene (IUPAC Poly(1-phenylethane-1,2-diyl)), abbreviated following ISO Standard PS, is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is one of the most widely used kinds of plastic are shortened to PP and PS respectively. In the United Kingdom The United Kingdom of Great Britain and Northern Ireland[note 7] is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of the island of Ireland, and many small islands. Northern Ireland is the only part of the UK with a land the polymer is commonly called polythene, although this is not recognized scientifically.

The ethene Ethylene is a gaseous organic compound with the formula C2H4. It is the simplest alkene (older name: olefin from its oil-forming property). Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and also has a role in biology as a hormone. Ethylene is the most molecule (known almost universally by its common name ethylene) C2H4 is CH2=CH2, Two CH2 groups Methylene groups in a chain or ring contribute to its size and lipophilicity. Methylene was also the old original name for methanol connected by a double bond, thus:

Polyethylene contains the chemical elements A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of and hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its.

Polyethylene is created through polymerization In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains. There are many forms of polymerization and different systems exist to categorize them of ethene. It can be produced through radical polymerization Radical polymerization is a type of polymerization in which the reactive center of a polymer chain consists of a radical, anionic addition polymerization An anionic addition polymerization of vinyl monomers is an addition polymerization initiated by a strong base and anion, such as an alkali amide, or an organometallic compound, such as n-butyllithium, ion coordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups that influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.

Classification

Polyethylene is classified into several different categories based mostly on its density The density of a material is defined as its mass per unit volume. The symbol of density is ρ . In some countries (for instance, in the United States), density is also defined as its weight per unit volume . The density of a substance is the reciprocal of its specific volume, a representation commonly used in thermodynamics and branching In polymer chemistry, branching occurs by the replacement of a substituent, e.g, a hydrogen atom, on a monomer subunit, by another covalently bonded chain of that polymer; or, in the case of a graft copolymer, by a chain of another type. In crosslinking rubber by vulcanization, short sulfur branches link polyisoprene chains into a multiply-. The mechanical properties of PE depend significantly on variables such as the extent and type of branching In polymer chemistry, branching occurs by the replacement of a substituent, e.g, a hydrogen atom, on a monomer subunit, by another covalently bonded chain of that polymer; or, in the case of a graft copolymer, by a chain of another type. In crosslinking rubber by vulcanization, short sulfur branches link polyisoprene chains into a multiply-, the crystal structure and the molecular weight The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit(s) u (equal to 1/12 the mass of one atom of the isotope carbon-12). This is numerically equivalent to the relative molecular mass of a molecule, frequently referred to by the term molecular weight, which is the ratio of the mass of that. With regard to sold volumes, the most important polyethylene grades are HDPE, LLDPE and LDPE.

UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight makes it a very tough Toughness, in materials science and metallurgy, is the resistance to fracture of a material when stressed. It is defined as the amount of energy per volume that a material can absorb before rupturing material, but results in less efficient packing of the chains into the crystal structure In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry. Patterns are located upon the points of a lattice, which is an array 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 rigid container with a neck that is narrower than the body and a "mouth". By contrast, a jar has a relatively large mouth or opening. Bottles are often made of glass, clay, plastic, aluminum or other impervious materials, and typically used to store liquids such as water, milk, soft drinks, beer, wine, cooking oil, medicine, handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks and butchers' chopping boards. It competes with Aramid Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a shortened form of "aromatic polyamide". They are fibers in which the chain molecules in bulletproof vests A ballistic vest, bulletproof vest or bullet-resistant vest is an item of personal armor that helps absorb the impact from firearm-fired projectiles and shrapnel from explosions, and is worn on the torso. Soft vests are made from many layers of woven or laminated fibers and can be capable of protecting the wearer from small caliber handgun and, under the tradenames Spectra and Dyneema, and is commonly used for the construction of articular portions of implants An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, which is a transplanted biomedical tissue. The surface of implants that contact the body might be made of a used for hip Hip replacement , is a surgical procedure in which the hip joint is replaced by a prosthetic implant. Replacing the hip joint consists of replacing both the acetabulum and the femoral head. Such joint replacement orthopaedic surgery generally is conducted to relieve arthritis pain or fix severe physical joint damage as part of hip fracture and knee replacements Knee replacement, or knee arthroplasty, is a surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve the pain and disability of osteoarthritis. It may be performed for other knee diseases such as rheumatoid arthritis and psoriatic arthritis. In patients with severe deformity from advanced rheumatoid arthritis, trauma,.

HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts A Ziegler-Natta catalyst is a catalyst used in the production of polymers of 1-alkenes . Ziegler-Natta catalysts are typically based on titanium compounds and organometallic aluminium compounds, such as the undefined methylaluminoxane (MAO) or well defined triethylaluminium, (C2H5)3Al or metallocene A metallocene is a compound with the general formula 2M consisting of two cyclopentadienyl anions (Cp, which is C5H5-) bound to a metal center (M) in the oxidation state II. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium Chromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρώμα), meaning color, catalysts or Ziegler-Natta catalysts) and reaction conditions. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes. One third of all toys are manufactured from HDPE. In 2007 the global HDPE consumption reached a volume of more than 30 million tons.[6]

PEX is a medium- to high-density polyethylene containing cross-link Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of cross-links to promote a difference in the bonds introduced into the polymer structure, changing the thermoplast into an elastomer An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred when referring to vulcanisates. Each of the monomers. 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.

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.

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 A heteropolymer or copolymer is a polymer derived from two monomeric species, as opposed to a homopolymer where only one monomer is used. Copolymerization refers to methods used to chemically synthesize a copolymer of ethylene with short-chain alpha-olefins Alpha-olefins are a family of organic compounds which are olefins or alkenes with a chemical formula CxH2x, distinguished by having a double bond at the primary or alpha (α) position. See the illustration below. This location of a double bond enhances the reactivity of the compound and makes it useful for a number of applications (for example, 1-butene 1-Butene is an organic compound and one of the isomers of butene. The formula is C4H8, 1-hexene 1-hexene is a higher olefin, or alkene, with a formula C6H12. 1-hexene is an alpha-olefin, meaning that the double bond is located at the alpha position, endowing the compound with higher reactivity and thus useful chemical properties. 1-hexene is an industrially significant linear alpha olefin and 1-octene 1-Octene is a higher olefin, or alkene, with a formula C8H16. 1-Octene is an alpha-olefin, meaning that the double bond is located at the alpha position, endowing this compound with higher reactivity and thus useful chemical properties. 1-Octene is one of the important linear alpha olefins in industry). LLDPE has higher tensile strength than LDPE, 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 is not as easy to process. LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. Cable covering, 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. In 2009 the world LLDPE market reached a volume of almost 24 billion US-dollars (17 billion Euro).[7]

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 mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry. Patterns are located upon the points of a lattice, which is an array as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction In physics, chemistry, and biology, intermolecular forces are forces that act between stable molecules or between functional groups of macromolecules. Intermolecular forces include momentary attractions between molecules, diatomic free elements, and individual atoms. These forces, most notably London Dispersion forces, dipole-dipole interactions is less. This results in a lower tensile strength and increased ductility. 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. In 2009 the global LDPE market had a volume of circa 22.2 billion US-dollars (15.9 billion Euro).[8]

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.

Recently 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 1 in 100 or 1,000 branches per backbone carbon, can significantly affect the rheological properties of the polymer.

Ethylene copolymers

In addition to copolymerization with alpha-olefins, ethylene can also be copolymerized with a wide range of other monomers and ionic composition that creates ionized free radicals. Common examples include vinyl acetate (the resulting product is ethylene-vinyl acetate copolymer, or EVA, widely used in athletic-shoe sole foams) and a variety of acrylates (applications include packaging and sporting goods).

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