Production of Polyethylene

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

Form Low density polyethylene (LDPE) High density polyethylene (HDPE)  

Name of process - Ziegler-Natta process

Requirements

High 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 process

The 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 way

Unbranched polyethylene molecules that are able to pack closely together in an orderly fashion

Molecular weight of molecules formed

Up to 1 000 000 g/mol Up to 3 000 000 g/mol

 Recycling symbol

The production processes for polyethylene

Structure of polyethylene