Production of Polyethylene

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Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer

There are two forms of polyethylene that can be produced via different production processes – high and low density.

FormLow density polyethylene (LDPE)High density polyethylene (HDPE)
Name of processZiegler-Natta process
RequirementsHigh pressure (1000 to 3000 atmospheres), high temperature (300°C), and an initiator (usually an organic peroxide)Pressure of a few atmospheres, temperatures of about 60°C, and a catalyst
Polymerisation processThe peroxide initiator splits to form free radicals, which allow the initiation of the joining of ethylene monomers (the initiator is not a catalyst as it gets incorporated into the polymer)The polymerisation occurs on the surface of the catalyst
Branching of polymer formed
Significant chain branching, meaning that polymer chains cannot pack closely together or in an orderly wayUnbranched polyethylene molecules that are able to pack closely together in an orderly fashion
Molecular weight of molecules formedUp to 1 000 000 g/molUp to 3 000 000 g/mol
 Recycling symbol

The production processes for polyethylene

Structure of polyethylene