West Lothian Council
Lorna C. Webster
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Plastics
Read
We already know that oil can be separated into many useful substances (eg
petrol, diesel, kerosine) using fractional distillation but oil is also used as
the raw material for making other substances. Oil is the raw material that
is used to make plastics.
Plastics are relatively new materials. They are man-made in the chemical
industry. This means that they are synthetic materials.
Since the invention of plastic around 1940 there
has been an explosion of the variety of uses for
different plastics. Glass, paper and metal have
been replace by plastics in many uses eg all milk
and juice bottles 50 years ago were made of
glass but now these are mainly made from
plastic.
The table below shows the names of some plastics and what they are used
for.
Name of plastic
Polythene
Polyvinyl chloride (PVC)
Polystyrene
Perspex
Formica
nylon
silicone
Kevlar
Bakelite
Lorna C. Webster
uses
plastic bags, bin liners,
washing-up bowls, pen casings
window frames, clothing,
guttering
coffee cups, packaging
material, ceiling tiles
spectacle lenses, safety
screens
plates, tumblers, kitchen work
tops
clothing, ropes, toothbrushes
waterproofing, plastic surgery
Bullet proof vests, bikers
clothing
electric plugs and switches
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Write a heading and try the work below.
1. What is the raw material that is used to make plastics?
2. Why are plastics called synthetic materials?
3. Think of a room in your house and make a list of all of the things that
are made of plastic.
4. Use the table to make a list of the names of all of the plastics.
5. Choose four plastics from your list and draw a picture for each to show
what they are used for.
Properties of plastics
Read
Plastics have many useful properties. They are electrical insulators, are
light, waterproof and airtight. Some plastics are flexible, some are
tough and some are elastic. Many plastics can be melted and moulded
into a huge variety of shapes.
Different plastics are chosen for different uses depending on their
properties.
Plastics are used to cover electrical wire because they are
electrical insulators and help prevent electrocution.
A waterproof plastic would be needed for a shampoo
container to stop the shampoo leaking out.
An airtight plastic would be needed for a food container to
help stop air and bacteria getting in.
Plastics are good for making containers like bottles because
they can be melted and moulded into shape.
In the past glass did the same job as plastics but
it is an advantage to use plastic now as plastic
bottles are lighter. This makes them cheaper to
transport than glass bottles.
Plastics are durable. This means that they will
last a long time. Nylon clothing lasts longer
than cotton clothing but sometimes natural
materials are better eg wool is warmer than
nylon or polyester.
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Write a heading and try the work below.
1. Make a list of some properties of plastics.
2. Why is plastic good for making a shampoo bottle?
3. Why can plastic containers have lots of different shapes?
4. Why is it cheaper to transport washing-up liquid in plastic bottles than
in glass bottles?
5. What does durable mean?
6. Write down one advantage that plastics have over natural materials for
making clothes.
7. Write down one disadvantage of using plastics instead of natural
materials for clothes.
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Problems with plastics
Read
Although plastics have many useful properties, their use can cause
problems. Plastics are durable (last a long time) and are often very light.
If you ever look at the street after lunchtime or after a concert or a football
match you will often notice a lot of the litter that is left lying around is
made of plastic. Plastic litter can cause problems for two main reasons.
1. Many plastics are light and
this means that litter from
plastic can be spread over a
very large area by the wind.
This means that it is more
difficult and expensive to clean it up.
2. Most plastics are non-biodegradable. This means that they will not be
rotted away by bacteria and will still be causing litter hundreds of years
later. A paper bag would be better as it is biodegradable and will rot away
because it will be eaten by bacteria.
Even once the bin men have collected the plastic, it is very difficult to get
rid of because if we try to burn plastics, toxic gases are made. One toxic
gas that is made is called carbon monoxide. This
gas starves the blood of oxygen and can kill.
Apart from incinerating plastics we also try to dispose
of them by burying them but even this does not solve
the problem for long.
Another problem with
plastics is what they are made
from. You already know that
crude oil is running out fast.
To make the oil last longer
we need to find ways to use
less plastics or to recycle the
ones we already have but
recycling can be difficult due
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to the large number of different kinds of plastic that we have.
There are many scientists employed in research
companies to find out about making plastics without
using oil.
Write a heading and try the work below in your jotter.
1. Imagine you are walking home after a concert or football match one
night. Make a list of all the litter you might see and what it is made of.
2. Why is the litter from plastics often spread over large areas?
3. What affect does this have on the cost of cleaning it up?
4. What does non-biodegradable mean?
5. Why is the fact that plastics are non-biodegradable a problem?
6. What is the problem with burning plastics?
7. Give an example of the name of a toxic gas that is made when a plastic
is burned and say why it can kill.
8. Describe what we can do to help make oil last longer.
9. Why is recycling plastics sometimes difficult?
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Types of plastics
Read
Although there are many different plastics, they can be split up into two
groups. One group of plastics is called thermoplastics and the other
group is called thermosetting.
To investigate the difference between these types of plastic collect
experiment card 2.56 and try the experiment.
Write a heading and try the work below.
1. What are the two groups of plastic called?
2. What did you notice happened to the thermoplastic in the experiment?
3. What happened to the thermosetting plastic when it was heated?
4. Copy and complete the sentences below by choosing the correct
answers.
Thermoplastics are plastics that will soften/harden when they
are heated. This means that they can/cannot be reshaped over
and over again.
Thermosetting plastics do/do not soften when they are heated.
This means that they can/cannot be reshaped because they
do/do not melt.
Use of thermoplastics and thermosetting plastics
Read
Thermoplastics are plastics that will soften when heated and so can be
melted and moulded into lots of different shapes.
Most plastics are thermoplastics eg polythene, polypropene, polystyrene,
perspex and nylon. Washing -up bowls, pens, bottles and other containers
are made of thermoplastics as they can be easily moulded into different
shapes.
If a thermosplastic is heated up too much it will
melt so thermoplastics are no good for making
kettles or pot handles.
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Thermosetting plastics are plastics that do not melt when heated.
Bakelite and formica are the names of two thermosetting plastics. They
are often used to make pot handles,
cooker controls, oven controls and
kettles because they will not melt when
these things get hot.. Thermosetting
plastics are used to make electrical
plugs and sockets because they are
electrical insulators but also if a short
circuit happens the plastic will not melt
and so this helps stop someone being electrocuted.
The two most important properties of thermosetting plastics is that they
don't melt and they are electrical insulators.
Write a heading and try the work below.
1. Make a list of some things that a thermoplastic would be used to make.
2. Why is it easy to make these shapes with a thermoplastic?
3. Make a list of the things that a thermosetting plastic would be used to
make.
4. Why would a thermoplastic be no good for making a kettle?
5. Why is it important to use a thermosetting plastic for making electrical
plugs and wires?
6. What are the two most important properties of thermosetting plastics?
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The chemistry of making plastics
Read
Plastics are very large chemical molecules called polymers. The
polymers are made by joining lots of smaller molecules together. The
small molecules that join up are called monomers. When a plastics is
made the monomers are forced to join up to make a polymer the reaction
is called polymerisation.
+
+
+
+
polymer (plastic)
monomers
polymerisation reaction
Write a heading and try the work below.
1. Are plastics large of small molecules?
2. What is the special name for a large molecule like a plastic?
3. How is a polymer made?
4. What are the small molecules that join up called?
5. When a plastic is made what is the name of the type of reaction.
6. Copy the diagram showing how monomers can join up to make a
polymer molecule.
7. a) Collect ten paper clips - these are your monomers.
b) Do a polymerisation reaction with the clips (join them together).
c) Make a drawing of the polymer you have made.
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Naming plastics
Read
It is very easy to work out the name of a plastic if we know the name of
the monomer that was used to make it.
eg 1. If we use a monomer called ethene the plastic we can make will be
called poly(ethene).
eg 2. If we use a monomer called styrene, the plastic we can make will be
called poly(styrene).
It is also easy to work out the name of a monomer if we know the name of
a plastic
eg. the plastic that is called poly(propene) is made from monomers called
propene.
Write a heading and try the work below.
1. What is the name of the plastic that would be made from a monomer
called
a) ethene?
b) styrene?
2. What is the name of the monomer that would be used to make the
plastic called poly(propene)?
3. Copy and complete the table below.
name of monomer
vinyl chloride
tetrafluoroethene
name of plastic
poly(vinyl chloride)
poly(chloroethene)
poly(propylene)
Check with your teacher if you have time to make your own polymer
(experiment card 2.54)
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