ADVANTAGES AND DISADVANTAGES OF PLASTICS
NAME OF USE ADVANTAGES DISADVAN-PLASTIC TAGES Polyester Clothing Light, cheap, Flammable,
flexible easily melted,
polluting due to
decomposition Polystyrene Packaging
Epoxy resin Glue
WHAT ARE POLYMERS AND PLASTICS?
; Polymers are long-chain molecules. They may be natural (e.g.
silk, wool, protein) or synthetic (e.g. polyester). ; Plastics are flexible synthetic long – chain molecules (polymers).
They are made from joining many smaller molecules
(monomers) together. The raw materials for making plastics
come from crude oil and the petrochemical industry. ; Examples of Plastics include bakelite, nylon, polyester and PVC
HOW ARE PLASTICS MADE?
; Polymerisation is the chemical reaction that joins repeating
units called monomers together to form polymers. There are
two types of polymerisation reactions.
; Two Polymerisation Reactions:
1. Addition Polymerisation occurs when the double bonds of
hydrocarbons called alkenes are broken, and then joined
into a long – chain molecule (e.g. Many ethene molecules
join to form polyethene in plastic bags).
2. Condensation Polymerisation occurs when two types of
monomers join to form a long – chain polymer and water
is given off (e.g. Many molecules of urea and
formaldehyde are joined to form glue).
1. What are 2 natural polymers?
2. What are 2 synthetic or man-made polymers?
3. Proteins are made of smaller units called amino acids. Which is
the monomer and which is the polymer?
4. Polythene (actually it is polyethene) is made of many ethene
molecules. Which is the monomer and which is the polymer?
5. Of what smaller monomers is PVC (polyvinyl chloride) made?
6. In addition polymerisation, alkenes such as ethene are joined.
First, the double bonds are broken and then all the ethene
molecules are joined into a very long chain. Using the
monomers of ethene as a guide, draw a portion of the long-
chain polymer called polythene.
H H H H H H
C C C C C C
H H H H H H
SOME PLASTICS MELT AND SOME DON’T –
WHAT ARE THE TWO TYPES OF PLASTICS ?
; Thermoplastics consist of long chains with no cross – links that
allow the molecules to slide over each other when heated. This
allows them to be moulded into new shapes. Common
examples are polyethene in plastic bags, nylon, polyvinyl
chloride (PVC), perspex and polystyrene.
; Thermosetting Plastics have cross-linking between many
molecules and they cannot slide over each other. Once they are
first set into a certain shape, they cannot be remoulded. If they
are heated, they will not melt but will eventually burn. Common
examples are bakelite in light switches and saucepan handles,
polyurethanes and epoxy resins.
WHAT ARE THE 3 WAYS OF SHAPING PLASTICS ?
Plastics can be moulded into objects in 3 main ways: 1. Injection moulding
3. Blow moulding
; Injection moulding consists of heating a thermoplastic and
injecting it into a mould where it cools and hardens into the new
; This process is fast and economical for producing large
numbers of objects.
; Injection moulding leaves a small line on the object where the
mould splits to allow the object to be taken out. ; Examples: cups, bottle caps, dessert bowls
; Softened thermoplastics are forced through an opening in a
piece of metal called a die. Once through the die, the plastic
cools and hardens.
; The shape of the die determines the cross-section of the object. ; Examples: pipes, tubes, straws and plastic rods
; A small amount of thermoplastic is softened by heating, and
then expanded by compressed air to fill the walls of a mould. ; Blow moulding is fast and economical for making hollow items. ; Examples: softdrink bottles
7. What type of plastic melts when heated and can be reshaped?
8. What type of plastic does not melt but will eventually burn if
9. Which plastic type – thermoplastic or thermosetting plastic – is
best for plumbing pipe, the plastic of an electric hairdryer, a
haircomb and a drinking straw?
10. Match the following:
A. extrusion X. plastic milk bottle
B. injection moulding Y. bathroom pipes
C. blow moulding Z. drinking cup
11. At ‘Fast Fred’s Fabulous Feast’ takeaway shop, you buy a
hamburger in an enclosed polystyrene container and a Coke in
polyethene plastic cup with a lid and a straw. Describe how
these packaging products are made.