Polyethylene

PE, or Polyethylene, is a chemically resistant plastic that can be very durable. Polyethylene plastic comes in a low density form and a high density form

History

Polyethylene is the largest volume polymer produced globally, with a total over 90 million metric tons per annum. Since its accidental discovery in 1933 it has evolved into a material critical to modern life. The first product commercialized was low density polyethylene (LDPE) based on free radical polymerization. Shortly thereafter new polymerization chemistries based on chromium catalysis and Ziegler Natta catalysis expanded the product space. Improved polymer performance based on new catalyst and application technologies have made it possible to have the diversity of use we see today. It is an essential material to power transmission, food packaging, consumer goods, electronics, household goods, industrial storage, transportation industries. Developments in technology continues to improve its functionality making polyethylene the most efficient use of natural resources petroleum and natural gas.

Properties

Polyethylene is capable of being moulded, extruded and cast into many various shapes. It is often used in construction as it is cheap and can be shaped or moulded easily, this is why it is appropriated to be used for the jobs such as guttering.

Polyethylene is a hard, stiff, strong and a dimensionally stable material that absorbs very little water. It has good gas barrier properties and good chemical resistance against acids, greases and oils. It can be highly transparent and colourless but thicker sections are usually opaque and off-white. Polyethylene also has good self extinguishing properties and resistance against ultra violet.

Applications

Polyethylene is a polymerized ethylene resin, used especially for containers, kitchenware, and tubing, or in the form of films and sheets for packaging. It is also a component in plastic bottles.

Processes

Polyethylene is derived from either modifying natural gas (a methane, ethane, propane mix) or from the catalytic cracking of crude oil into gasoline. In a highly purified form, it is piped directly from the refinery to a separate polymerisation plant. Here, under the right conditions of temperature, pressure and catalysis, the double bond of the ethylene monomer opens up and many monomers link up to form long chains.

Today, polyethylene manufacturing processes are usually categorized into "high pressure" and "low pressure" operations. The former is generally recognized as producing conventional low density polyethylene (LDPE) while the latter makes high density (HDPE) and linear low density (LLDPE) polyethylenes. The difference between these polyethylene processes and types is outlined below.

Recycling

Recycled Polyethylene is made by taking plastic that has been disposed and regrinding it into usable resin. It can then be blended with virgin polyethylene, extruded into film and converted into bags and tubing. Recycled Polyethylene is not as clear as virgin polyethylene.
There are two types of recycled polyethylene:

Post-Consumer Recycled Polyethylene (PCR PE) are plastics made from the consumer stream of waste – bottles, caps and recycled plastic bags collected in commercial and residential recycling programs. Due to the variety of polyethylene materials used, PCR PE can have a wide range of densities. Due to these inconsistencies, PCR PE has to be blended with virgin polyethylene to make film. And since the recycled materials are contaminated with impurities (dirt, cellulose, and inorganic materials), the amount of virgin PE that needs to be blended is dependent on the quality of the PCR PE.
Post-Industrial Recycled Polyethylene (PIR PE and aka Pre-Consumer Polyethylene) – polyethylene film leftover from either extruding film or converting it into bags and tubing. Resin makers do not face the same challenges making PIR PE as they do PCR PE due to minimal impurities (dust) and absence of density variations. Therefore, PIR PE made using 100% recycled content is possible.