Polyethylene focus

Regional producers are investing heavily in polyethylene to meet the Asian demand.

Polyethylene is the polymer that we see most in our daily life. It is a thermoplastic commodity heavily used in consumer products (notably the plastic shopping bag). This is the polymer that makes shampoo bottles, children's toys, and even bullet proof vests. For such a versatile material, it has a very simple structure, the simplest of all commercial polymers. A molecule of polyethylene is nothing more than a long chain of carbon atoms, with two hydrogen atoms attached to each carbon atom.

Historically, a German scientist, Hans von Pechmann, discovered a waxy residue at the bottom of his test tube. He had little idea of the material's significance, he was not to know that the substance was an early form of what we now use to bottle our shampoo, cocoon our sandwiches and wrap our wires. He had, completely by accident, made polythene, one of the world's most widely used and controversial materials.

The product Von Pechmann made that day in 1899 was virtually identical to the modern chemical and a pair of his colleagues - Eugen Bamberger and Friedrich Tschirner - called it polymethylene. But unlike polythene, which is versatile enough to make hardy and filmic plastics, this waxy resin was not useful in practical terms, and so little was made of it.

Different grade

Polyethylene is classified into several different categories based mostly on its density and branching. The mechanical properties of PE depend significantly on variables such as the extent and type of branching, the crystal structure and the molecular weight.

The most famous grades of polyethylene are High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE) and the Linear Low Density Polyethylene (LLDPE).

"When you decide to invest in polyethylene, you have to choose what grade to produce before building the plant, you can't change that later," says Richard Roudex, vice president of PE Europe at Lyondellbasell company.

To produce one tonne of HDPE you need 1.05 tonnes of ethylene, and for one tonne of LDPE you need 1.03 tonnes of ethylene according to International Chemical Information System (ICIS) conversion table.

High density polyethylene (HDPE) is the third largest thermoplastic commodity after polyvinyl chloride and polypropylene. It is typically used to produce pipe for water, gas and irrigation, and electrical conduit. Film and sheet made from HDPE are used in a wide range of applications including wrapping, refuse sacks, carrier bags and industrial liners.

Global HDPE demand shrank by 2.1% in 2008 compared to 2007 according to Nexant Chemsystem . HDPE would recover growth as the industry restocked and as the economic outlook improved, Asia would command approximately half of the projected growth.

Low density polyethylene (LDPE) is the oldest and most mature of the polyethylene. The largest market for LDPE is film applications, which is split roughly 50-50 between packaging and non-packaging applications. In food packaging applications such as meat and poultry wrapping, frozen food bags and bag-in-box packaging for liquids. Non-food packaging applications include carry-out bags, waste bin liners and construction and agricultural films.

A growth area for LDPE is the extrusion coating of paper and paperboard, the second largest application segment. This is largely due to innovations in packaging technology for paperboard coating, paper and foil.

Globally, LDPE is predicted by consultants to grow at around 2% per year. In the US and west European markets, demand is stagnant or only growing slightly but higher at 3-4% per year in eastern and central Europe. In China, it is higher still at 5-6% per year.

Linear low density polyethylene (LLDPE) is a thermoplastic which in many applications replaces its predecessor low density polyethylene (LDPE) or used in blends with LDPE. In particular, LLDPE's short chain branching gives it higher tensile strength, puncture and anti-tear properties, making it suitable for film applications.

Globally, over 80% of LLDPE goes into film applications such as food and non-food packaging, shrink/stretch film and non-packaging uses. Major growth areas are high clarity packaging, high barrier thin films and ‘active' packaging that increases shelf life and enhances flavours. Growth is also occurring from the transition of items presently packaged in rigid containers to high quality flexible packages.

Meanwhile, the development of new catalysts is expected to enable LLDPE to penetrate new non-polyethylene markets such as metals, paper, glass and PVC.

LLDPE consumption fell an estimated 1.2% in 2008, after growing 5.6% in 2007 according to Nexant Chemsystems.

But even with all these differences, every grade of polyethylene is important."Each (HDPE, LLDPE, LDPE) has multiple and varied applications, from flexible packaging to health & hygiene; therefore no one can say any one is the best polymer," says Zuhair Allawi, commercial director at Dow Chemical India, Middle East and Africa.

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