Industrial Importance of Alkenes
The Importance of Alkenes in Plastic Synthesis
Many technical developments are based on plastics. Modern audio and video equipment, for example movies, video tapes and cassettes, recording tapes, overhead transparencies, compact discs, etc., would not exist in its present form without the availability of polymeric materials. Since plastics can be manufactured to fit the specifications of nearly every application their advantages are obvious.
Today, the starting materials for plastic synthesis are almost exclusively derived from petroleum and natural gas. The important monomer ethylene, for example, is produced by steam cracking of aliphatic hydrocarbons at 800 °C. If petroleum (naphtha) is applied to the steam cracking process, a mixture of different hydrocarbons is produced from which ethylene can be separated.
Polyethylene, representing nearly twenty percent of all synthetic, polymeric material, is the plastic most frequently produced. The polymerization can be carried out at high, medium and low pressure. Polyethylene prepared at high-pressure is highly branched. Therefore, its density and degree of crystallinity are low (LDPE = low density polyethylene). The properties of polyethylene can be widely varied by selectively applying different reaction conditions. Since the early eighties, a special polyethylene is being produced that exhibits high optical transmittance and mechanical stability (LLDPE = linear low-density polyethylene). Medium- and low-pressure polyethylenes predominantly contain unbranched chains resulting in high density, degree of crystallinity and mechanical stability (HDPE = high-density polyethylene).