polyethylene(redirected from Polymethylenes)
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polyethylene(pŏl'ēĕth`əlēn), widely used plasticplastic,
any organic material with the ability to flow into a desired shape when heat and pressure are applied to it and to retain the shape when they are withdrawn. Composition and Types of Plastic
..... Click the link for more information. . It is a polymerpolymer
, chemical compound with high molecular weight consisting of a number of structural units linked together by covalent bonds (see chemical bond). The simple molecules that may become structural units are themselves called monomers; two monomers combine to form a dimer,
..... Click the link for more information. of ethyleneethylene
, H2C=CH2, a gaseous unsaturated hydrocarbon. It is the simplest alkene. Ethylene is colorless, has a faint odor, and has a slightly sweet taste; it melts at −169.4°C; and boils at −103.8°C;.
..... Click the link for more information. , CH2=CH2, having the formula (-CH2-CH2-)n, and is produced at high pressures and temperatures in the presence of any one of several catalystscatalyst,
substance that can cause a change in the rate of a chemical reaction without itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis.
..... Click the link for more information. , depending on the desired properties for the finished product. Polyethylene is resistant to water, acids, alkalies, and most solvents. Its many applications include films or sheets for packaging, shower curtains, unbreakable bottles, pipes, pails, drinking glasses, and insulation for wire and cable.
[—CH2—CH2—]n, a white thermoplastic polymer. It is produced industrially by polymerization of ethylene at high pressure (low-density polyethylene) or at low or medium pressure (high-density polyethylene).
The structure and properties of polyethylene are determined by the method of preparation. The average molecular weight of the most common brands is 30,000–800,000; crystallinity and density at 20°C are 50 percent and 0.918–0.930 g/cm3, respectively, for low-density polyethylene and 75–90 percent and 0.955–0.968 g/cm3 for high-density polyethylene. An increase in density is accompanied by an increase in hardness, modulus of bending resilience, yield point, and chemical stability. Polyethylene combines high tensile strength (10–45 meganewtons per sq m, or 100–450 kilograms-force per sq cm) with elasticity (ultimate elongation, 500–1,000 percent), and it has good electrical insulation properties (loss tangent, 2 × 10–4 to 4 × 10–4 at –120° to 120°C and 10–50 kilohertz). It is resistant to alkalies in any concentration, and also to organic acids, concentrated hydrochloric, and hydrofluoric acids, but it is attacked by nitric acid, chlorine, and fluorine. At temperatures above 80°C, it is soluble in aliphatic and aromatic hydrocarbons and their halogen derivatives. It is relatively stable upon exposure to radioactive emissions, and it is harmless. Its working temperature range is between –80°–120° to 60°–100°C.
Polyethylene is one of the least expensive polymers, combining valuable properties with workability by all known high-productivity methods used for thermoplasts. It is first among polymer plastics in world production.
Polyethylene is used to make films, pipes (including pipes for sewage and aggressive liquids, and also mains), sectional products, insulation for wires and cables, containers (large bottles, canisters, and tanks), electrolytic baths, sanitary products, and fibers; it is also widely used in engineering and agriculture, as well as domestically. Low-density polyethylene has become the most widespread. Products manufactured by means of chlorina-tion and sulfochlorination of polyethylene have also acquired commercial importance.
Polyethylene is manufactured in the USSR (high-density, or low-pressure, and low-density, or high-pressure, polyethylene) and abroad. Foreign brands of high-density polyethylene include Marlex (USA), Hostalen and Vestolen (Federal Republic of Germany), Hi-Zex (Japan), and Eltex (Italy). Foreign low-density brands include Bakelite and Alathon (USA), Alkathene (Great Britain), and Lupolen (Federal Republic of Germany). World production of polyethylene in 1973 was about 10 million tons.
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I. N. ANDREEVA