Lesson: Synthetic Fibres and Plastics

Exercise:

Explain why some fibres are called synthetic.

Some fibres are called synthetic because they are man-made, prepared in factories by combining different types of chemicals.

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.

b

Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called ________or _________fibres.
(b) Synthetic fibres are synthesised from raw materials called ________.
(c) Like synthetic fibres, plastic is also a _________.

(a) Synthetic fibres are also called artificial or man-made fibres.
(b) Synthetic fibres are synthesised from raw materials called petrochemicals.
(c) Like synthetic fibres, plastic is also a polymer.

Give examples which indicate that nylon fibres are very strong.

Nylon fibres are very strong and are used for manufacturing ropes used in mountaineering. They are also used to prepare parachutes.

Explain why plastic containers are favoured for storing food.

Plastic containers are favoured for storing food because they:

·         Do not react with the food stored in them

·         Are light weight and strong

·         Are easy to handle

·         Are cheap

·         Are ductile

Explain the difference between thermoplastic and thermosetting plastics.

Thermosetting plastic	Thermoplastic
These are inflexible and cannot be bent easily. If forced to bend, they might break.	They can be bent easily.
When heated, they do not get softened. Thus, they cannot be reshaped.	They bend easily when heated. Hence, they can be reshaped.

Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards

(a) The handles of saucepans are made of thermosetting plastics because it is a

poor conductor of heat, owing to which it does not get heated up while cooking, making it easier to handle. Moreover, it does not get softened due to heat.
(b) As thermosetting plastics are a poor conductor of electricity, it does not allow electric current to pass through it. Thus, it is safe to have electric plugs/switches/plug boards made up of thermosetting plastics.

Categorize the materials of the following products into 'can be recycled' and 'cannot be recycled'.
Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Cannot be recycled	Can be recycled
Telephone instruments	Plastic toys
Cooker handles	Plastic chairs
Electrical switches	Carry bags
	Plastic covering on electrical wires
	Ball point pens
	Plastic bowls

Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Rana should buy shirts made from cotton for summers. Cotton fabrics are good in absorbing water. In summers, they absorb body sweat, which when evaporate, cool the body.

Give examples to show that plastics are non-corrosive in nature.

We have seen that foods and chemicals are being stored in containers that are made of plastics. Foods stored in such containers remain unaffected for longer period. This can happen only if plastics are non-corrosive in nature i.e., they do not react with air, water, minerals, and other chemicals.

Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

The handle of a toothbrush should be hard and strong. So it should be made up of materials that are hard.

The bristles of the tooth brush helps in cleaning our teeth and so comes in contact with the tender skin inside our mouth. So it should be soft and flexible too.

Thus, the handle and bristles of a tooth brush should be made of different materials.

'Avoid plastics as far as possible'. Comment on this advice.

Plastics should be avoided as far and as much as possible because:

·         They take several years to decompose.

·         They are a source of pollution of land and water.

·         When burnt, they release poisonous gases into the atmosphere.

·         It is very difficult to dispose them off.

·         Bags made up of plastics, when carelessly thrown in an open garbage box, can cause death of stray animals.

·         They may cause for clogging of drains when thrown carelessly.

Match the terms of column A correctly with the phrases given in column B.

A		B
(i)	Polyester	(a)	Prepared by using wood pulp
(ii)	Teflon	(b)	Used for making parachutes and stockings
(iii)	Rayon	(c)	Used to make non-stick cookware
(iv)	Nylon	(d)	Fabrics do not wrinkle easily

A		B
(i)	Polyester	(d)	Fabrics do not wrinkle easily
(ii)	Teflon	(c)	Used to make non-stick cookware
(iii)	Rayon	(a)	Prepared by using wood pulp
(iv)	Nylon	(b)	Used for making parachutes and stockings

'Manufacturing synthetic fibres is actually helping conservation of forests'. Comment.

The synthetic fibres are obtained by chemical processing of petrochemicals. Manufacturing of synthetic fibres do not require cutting down of trees or hunting animals. Thus, if synthetic fibres meet the need for fibre, then unnecessary cutting down of trees or hunting of animals can be avoided. This helps in conservation of forests.

Describe an activity to show that thermoplastic is a poor conductor of electricity.

Activity:

To show that thermoplastic is a poor conductor of electricity.

Materials required:

·         A bulb

·         Few wires

·         A battery

·         A piece of metal

·         A plastic pipe

Activity:

(a)          Circuit with the metal

·         Set up the circuit first with the metal as shown in the figure.

·         Switch on the current.

·         You will observe that the bulb glows.

(b)   Circuit with the plastic pipe

·         Set up the circuit first with the plastic as shown in the figure.

·         Switch on the current.

·         You will observe that the bulb does not glow

Conclusion: A plastic pipe (thermoplastic) is a poor conductor of electricity.