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Alkanes: Sources and Relevance

Alkanes: Polymers

Alkanes play an important role in everyday life. Not only fuels but most of the economically important polymers belong to this class. Two of the most important representatives are polyethylene (PE) and polypropylene (PP).

Polyethylene (PE)

PE is made up of ethane units. Two types, HDPE (high density polyethylene) and LDPE (low density polyethylene), differ in the degree of branching and therefore exhibit different densities. The size of the molecules is easily to tell by their molecular mass. HDPE, for example, has a medium molecular mass of 200,000 - 5,000,000 g/mol. PE is easily to work with and is resistant against many solvents even at elevated temperatures. In 1953, Ziegler and Natta for the first time developed catalysts that allowed for the synthesis of PE to be carried out at room temperature and normal pressure, thus making PE one of the most important polymers. PE is especially being used in the manufacture of hollow goods and in injection molding, e.g. bottles, canisters, sheets, and gas-proof pipes. In 1990, consumption of polyethylene in the USA, Japan and Western Europe amounted to ca. 19 million tons

Fig.1
Polyethylene

Polypropylene (PP)

PP, made up of propane units, can also be synthesized at lower temperatures and has a medium relative molecular mass of 150,000 - 600,000 g/mol. Because of its high surface resistance and strength, PP is used for the manufacture of sheets. Additional applications include among others the manufacture of clothes, plastic foam, casings, carpets, and ropes. Contrary to PE, PP can neither be colored nor be printed on. In 1989, the global production of PP had a volume of 13.1 million tons.

Fig.2
Polypropylene
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