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=Polyethylene=

Polyethylene (a.k.a. PE) is the most popular plastic in the world. It makes many different items. For example, polyethylene makes, shower curtains, unbreakable bottles, pipes, pails, drinking glasses, insulation for wire and cable, grocery bags, shampoo bottles, children's toys, and bullet proof vests. Because of it's simple structure, it is a very versatile material. A polyethylene is a chain of carbon atoms each attached to two hydrogen atoms. Polyethylene is resistant to water, acids, alkalis, and most solvents. Polyethylene is a polymer. A polymer is a substance composed of molecules with a large molecular mass, connected by covalent bonds. Polyethylene is created through polymerization of ethene. This is the process of bonding single units to make longer chains. Polyethylene is categorized in many ways relating to it's density.

Ultra high molecular weight polyethylene Ultra low molecular weight polyethylene High molecular weight polyethylene High density polyethylene High density cross-linked polyethylene Cross-linked polyethylene Medium density polyethylene Low density polyethylene Linear low density polyethylene Very low density polyethylene (wikipedia.com)

**Classifications**


 * UHMWPE** is polyethylene with a molecular weight somewhere in the millions, usually between 3.1 and 5.67 million! The higher molecular weight it is becasue of efficient packing of the chains into the crystal structure. Because of its amazing toughness, cut, wear and outstanding chemical resistance, UHWMPE is used in a wide range of applications. These include can & bottle handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks, butchers' chopping boards.
 * HDPE** has a low degree of branching, so stronger and has stronger intermolecular forces and tensile strength. Its density is equal or greater than 0.941 g/cm3. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes.
 * PEX** is a medium- to high-density polyethylene containing cross-linked bonds. The high-temperature properties of the polymer are improved, its flow is lowered and its chemical resistance is greater. PEX is used in water plumbing systems, as 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** has a density, betwen .926-.940g/cm3. MDPE has good shock and drop resistance properties. It also is less sensitive than HDPE; which means that stress cracking resistance is enhanced. MDPE is commonly used in gas pipes & fittings, sacks, shrink film, packaging film, carrier bags, screw closures.



Different types of polyethylene can be produced in different ways. Polyethylene can be produced through Radical Polymerization, anionic addition polymerization, ion coordination polymerization and through cationic vinyl polymerization. Polymerization is when monomers are bonded to form longer polymers. Radical Polymerization is when the reactive center of the polymer chain has a radical. Anionic addition polymerization is created from a strong base anion. Ion coordination polymerization is when a monomer (small molecule) adds to a growing macromolecule (large molecule). Cationic addtion polymerization is when a large amount of monomers are added very quickly to form a larger polymer.



**HISTORY**

Polyethylene was synthesized by Hans von Pechmann in 1898, accidentally. He was a German chemist who was heating diazomethane. He realized it contained the long chain of Carbon and Hydrogen atoms. Weather or not it is observable depends on the melting point which is one-hundred twenty to one-hundred thirty degrees celcius. It also depends on the molecular weight. At a high-temperature, it is possible for polyethylene to be dissolved if it is in aromatic hydrocarbons or in chlorinated solvents.

**Linear Polyethylene**

Linear polyethylene is stronger than regualr polyethylene. When it comes to manufacturing polyethylene, linear polyethylene seems it would be better to use but it is much more expensive to make. Like we mentioned before, polyethylene can make bullet-proof vests. This requires ultra-high molecular weight polyethylene.

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http://pslc.ws/macrog/pe.htm

http://www.exxonmobilchemical.com/public_products/Polyethylene/Polyethylene/NorthAmerica/PE_ProductFrontPage.asphttp://

www.exxonmobilchemical.com/public_products/Polyethylene/Polyethylene/NorthAmerica/PE_ProductFrontPage.asp