So we talked about the properties of plastics. Since they are so varied this is why they have replace many more expensive materials such as metals.
Plastics can be split into two different groups – Thermoplastic – this group of plastics will melt on heating. This is a very useful property and means that these plastics can be made as granules and then heated and moulded into new shapes for whatever they are making. Thermosetting – This group of plastics do not soften on heating so therefore cannot be reshaped. They are usually tough materials with high melting points. E.g. Urea – methanal the plastic used in electrical plugs, pot handles and in kettles. I remember it as thermosetting think “set” so its set in shape and cant be remoulded.
A discarded plastic bottled (irn bru bottle) will remain in the environment for years as the plastics are very durable therefore plastics are said to be non-biodegradeable – that is cannot be (bio – living, degradeable – able to e broken down) broken down by the bacteria in the soil as other materials are. We use tones of plastic for packaging – think about a trip to the supermarket and how much packaging there is on everything.
Not all plastics are recylable – look for the triangle that says its recycleable and encourage people to in their homes with the blue bins.
So all plastics contain carbon and hydrogen so all plastics when burned will combine with oxygen through incomplete combustion to form carbon monoxide. This is a very poisonous gas that has no smell or colour and stops red blood cells carrying oxygen around the body. So when there are fires in peoples homes it is the fumes from the plastics in the home burning (e.g. your couch) that creates a cloud of poisonous gases. This is why firemen wear breathing apparatus Polyurethane plastics contain nitrogen and therefore when the burn te nitrogen can combine with the carbon and hydrogen in the plastic to form hydrogen cyanide (HCN) Polychloroethene – used in outdoor clothing, vinyl wallpaper – on burning this plastic gives off a choking acidic gas known as hydrogen chloride (HCl)
Get everyone in the room to stand around the outside of the room with their arms crossed across their chests. Get them to stretch their arms out and then to join hands so that we have broken the double bond in the ethene molecules (each pupil) and then formed a polymer (polyethene) Alternatively Give everyone a paper clip and ask them to join up with everyone else from the front row back so that they join up in the middle.
Polyethene is the most widely used plastic. The monomer belongs to the homologous series called the alkenes. Many alkenes are used to make polymers e.g. propene which can be polymerised to make poly(propene) which is used for car bumpers, carpets, car bumpers and even biscuit wrappers. All the monomers used in this kind of polymerisation must contain a C=C bond. These alkenes come from Crude oil – long chain alkanes are catalytically cracked to yield short chain alkanes and alkenes that are used as the monomers. Naming – Chlorethene becomes poly(chloroethene)
Properties of Plastics
• Flexible – you can squeeze the shampoo out of the
• Watertight – the shampoo will not leak
• Shatterproof – the bottle won’t break if dropped.
• Light – easy and cheap to transport
• Easily moulded – can make plastic into complicated
• Heat insulators – plastic vending machine cups.
• Durable, non biodegradable
• Electrical insulators – plugs and sockets are made of
What happens when we heat up
• Two groups of plastics:
• Thermoplastic – materials soften on
heating so can be moulded into new
• Thermosetting – plastics that do not
soften when heated, so cannot be
Problems with Plastics
• Non-biodegradable – do not decay when
• Large amounts of plastic thrown away
which ends up in landfill sites
• Some local authorities burn plastics to
dispose of them – needs to be controlled
to prevent dangerous fumes from being
• Re-use plastics – e.g. plastic bags
• Recycle at recycling points and at home
• Use biodegradable plastics – decay when
they come into contact with the soil
• Use less plastic - manufacturers could
use less for packaging
• Most of the
are made when
elements in the
plastics join with
oxygen in the air
to form new
Natural vs. Synthetic
Natural Materials e.g. wool, wood, paper
Can be expensive
Made from renewable
resources e.g. trees
Don’t last very long
Synthetic Materials e.g. plastics
Mass produced cheaply
Made from oil – finite
Useful properties – light,
Toxic fumes when burned
• Plastics are very large molecules called
polymers – ‘poly’ – many; ‘mer’- a part
This molecule is called polythene
• The plastic polythene is made by joining
molecules of ethene.
• The small ethene molecules that join together to
form the polymer are known as monomers
• Its correct name is poly(ethene) – to name a
polymer/plastic ‘poly’ then the (monomer unit) in
• Poly(ethene) is the most widely used plastic
Many ethene molecules
This process is known as polymerisation
• Polymers are formed when small molecules
known as monomers join together
• All the monomers in this kind of polymerisation
must contain C = C
• Each small monomer becomes a part of the
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