UKPCS Science Chemistry: Polyethylene #63

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Polyethylene (abbreviated PE) or polyethene is the most common plastic. The annual global production is around 80 million tonnes. Its primary use is in packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.). Many kinds of polyethylene are known, with most having the chemical formula (C2H4)n. PE is usually a mixture of similar polymers of ethylene with various values of n.

Polyethylene Properties:

Mechanical: Polyethylene is of low strength, hardness and rigidity, but has a high ductility.

Thermal: The usefulness of polyethylene is limited by its melting point of 80 °C.

Chemical: Polyethylene consists of nonpolar, saturated, high molecular weight hydrocarbons. they are not attacked by strong acids or strong bases, and are resistant to gentle oxidants and reducing agents. Polyethylene absorbs almost no water. PE can become brittle when exposed to sunlight, carbon black is usually used as a UV stabilizer. Polyethylene is a good electrical insulator.

MANUFACTRING:

The ingredient or monomer is ethylene (IUPAC name ethene), a gaseous hydrocarbon with the formula C2H4.Because the compound is highly reactive, the ethylene must be of high purity. Ethylene is a rather stable molecule that polymerizes only upon contact with catalysts. The conversion is highly exothermic. 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.


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