Polythene: introduction

Polythene is a synthetic material, which is polymerised from ethene. It is thermoplastic, which means that it can be softened by heat and remoulded. There are a number of forms of polythene including high density (HDPE) and low density (LDPE). Low density polythene is used for things like polythene bags, whereas washing-up bowls are likely to be made of high density polythene.

Some background

Eric Fawcett and Reginald Gibson discovered the polymerisation of ethene by accident on 24^th March 1933. This was a high pressure process, which was considered dangerous and was not repeated for two years. It is still the basis of making low density polythene. In the 1950s the German chemist, Karl Zeigler, developed catalysts that polymerised ethene at lower pressures and produced polythene with fewer branches than the high pressure process. This is called high density polythene and it is denser, stronger and harder to melt then low density polythene. Ziegler shared the 1963 Nobel prize with the Italian Giuglio Natta who also worked on catalysts for polymerisation.

Polythene: fact file

	Blow moulding (eg washing-up liquid bottles)	42%
	Injection moulding (eg buckets)	24%
	Film	16%
	Pipe	14%
	Other	4%

	Film (eg carrier bags)	76%
	Exterior coating	8%
	Injection moulding	5%
	Electrical cable insulation	4%
	Other	4%

Map	Aerial view of plant
Unlabelled process diagram	Labelled process diagram
Unlabelled reaction vessel diagram	Labelled reaction vessel diagram

Polythene: on the web

• www.pslc.ws/mactest/pe.htm
• www.ausetute.com.au/polythen.html
• www.bbc.co.uk/schools/gcsebitesize/chemistry/usefulproductsoil/alkanes_and_alkenesrev4.shtml

last update March 2006