Chapter 3
Synthetic Fibres and Plastics
Exercise Questions
1. Explain why some fibres are called synthetic.
Soln: Some fibres are called synthetic fibres
because they are man-made fibres prepared
using chemicals. These are made of small units
that join together to form long chains. Some
examples of synthetic fibres are nylon, rayon,
acrylic, polyester etc.
2. Mark the correct answer.
Rayon is different from synthetic fibres because
(a) it has a silk-like appearance.
(b) it is obtained from wood pulp.
(c) its fibres can also be woven like those of
natural fibres.
Soln: The answer is (b) it is obtained from wood
pulp.
3. Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called __________
or __________ fibres.
(b) Synthetic fibres are synthesised from the raw
material called __________.
(c) Like synthetic fibres, plastic is also a
__________
Soln: (a) Synthetic fibres are also
called artificial or man-made fibres.
(b) Synthetic fibres are synthesised from a raw
material called petrochemicals.
(c) Like synthetic fibres, plastic is also a polymer.
4. Give examples which indicate that nylon fibres
are very strong.
Soln: Following are the examples that indicate
nylon fibres are very strong:
• Parachutes and ropes of rock climbing are
made of nylon
• Nylon is used in making seat belts, fishing nets
and tyre cords.
• Nylon is used in making sports accessories
like rackets.
•
5. Explain why plastic containers are favoured for
storing food.
Soln: Plastic containers are favoured for storing
food because plastic is non-reactive and will not
react with the ingredients of the food items.
6. Explain the difference between thermoplastic
and thermosetting plastics.
Soln: The difference between thermosetting
plastics and thermoplastics are as follows:
Thermosetting Thermoplastics
plastics
It cannot be Thermoplastic
bent; it will can be bent
break if we easily
attempt to
bend
thermosetting
plastics
On heating On heating the
thermosetting thermoplastics,
plastics, they it becomes
cannot be softened and
softened. This can be
is the reason moulded and
it cannot be reshaped
reshaped easily.
once it is
moulded.
7. Explain why the following are made of
thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Soln:
a) Thermosetting plastics are used to make
saucepan handles because they are bad
conductors of heat, and also, on heating, these
plastics do not get softened.
b) Bakelite is a kind of thermosetting plastic which
is a bad conductor of heat and electricity. Because
of this property, it is used for making electric
plugs, switches, plug boards, etc.
8. Categorise the materials of the following
products into ‘can be recycled’ and ‘cannot be
recycled’.
Telephone instruments, plastic toys, cooker
handles, carry bags, ballpoint pens, plastic bowls,
plastic covering on electrical wires, plastic chairs,
electrical switches.
Soln:
Can be Cannot be
Recycled recycled
Plastic chairs Cooker
handles
Plastic bowls Electrical
switches
Plastic toys Telephone
instruments
The plastic
covering on
electrical
wires
Carry bags
Ballpoint
pens
9. Rana wants to buy shirts for summer. Should he
buy cotton shirts or shirts made from synthetic
material? Advise Rana, giving your reason.
Soln: Rana should buy a cotton shirt for the
summer and not a synthetic shirt. Cotton is a good
absorber of water. So it can soak the sweat
coming out of the body and expose it to the
environment. Thus, it helps in evaporating sweat
and helps in cooling the body.
10. Give examples to show that plastics are non-
corrosive in nature.
Soln: Plastics are non-corrosive in nature; they do
not react even if they come in contact with strong
chemicals. For example, the cleaning chemicals
that we use at home are stored in plastic bottles
instead of metal containers.
11. Should the handle and bristles of a toothbrush
be made of the same material? Explain your
answer
Soln: The handle and bristle of a toothbrush should
not be made of the same material, as the handle
of the toothbrush should be hard and strong while
the bristle should be soft and flexible.
12. ‘Avoid plastics as far as possible’. Comment on
this advice.
Soln: We should avoid plastics as far as possible
because plastics are non-biodegradable in
nature. Once introduced into the environment,
they cause pollution. If burnt, they release
poisonous gases, and the plastic bags thrown in
the garbage dump are swallowed by animals,
choking their respiratory system and causing
fatalities in them.
13. Match the terms of column A correctly with the
phrases given in column B
A B
(i) (a) Prepared by
Polyester using wood pulp
(ii) Teflon (b) Used for
making
parachutes and
stockings
(iii) (c) Used to make
Rayon non-stick
cookware
(iv) Nylon (d) Fabrics do not
wrinkle easily
Soln:
A B
(i) (d) Fabrics do not
Polyester wrinkle easily
(ii) Teflon (c) Used to make
non-stick
cookware
(iii) (a) Prepared by
Rayon using wood pulp
(iv) Nylon (b) Used for
making
parachutes and
stockings
14. ‘Manufacturing of synthetic fibres is actually
helping conservation of forests’. Comment.
Soln: The manufacturing of synthetic fibres is
helpful in the conservation of forests because if we
use natural fibres, the raw materials for them
have to be derived from plants, which requires
cutting off lots of trees. This proves to be helpful in
the conservation of forests.
15. Describe an activity to show that thermoplastic
is a poor conductor of electricity
Soln: In order to show that thermoplastic is a poor
conductor of electricity, we will design a circuit.
For that, we need a bulb, some wires, a battery, a
piece of metal and a plastic pipe (as shown in the
figure below). After setting the experiment, switch
on the current, and you will observe that the bulb
glows in the former case. In the latter case, the
bulb does not glow. Hence, a plastic pipe (which is
a thermoplastic) is shown to be a poor conductor
of electricity.
