PLASTICS

• Plastics are synthetic (man-made) materials that can be easily shaped and moulded.
• Most plastics are polymers. The structure of polymer molecules gives plastic different properties.
• Long chains of molecules that slide over each other easily make flexible plastics such as polythene. Tangled chains make rigid plastics such as melamine.
• Typically plastics are made by joining carbon and hydrogen atoms. These form ethane molecules, which can be joined to make a plastic called polythene.
• Many plastics are made from liquids and gases that are extracted from crude oil.
• Thermoplastics are soft and easily moulded when warm but set solid when cool. They are used to make bottles and drainpipes and can be melted again.
• Thermoset plastics, which cannot be re-melted once set, are used to make telephones and pan handles.
• Blow moulding involves using compressed air to push a tube of plastic into a mould.
• Vacuum moulding involves using a vacuum to suck a sheet of plastic into a mould.
• Extrusion moulding involves heating plastic pellets and forcing them out through a nozzle to give the right shape.