Science NCERT Grade 8, Chapter 3, Synthetic Fibres and Plastics deals majorly with the fundamentals of synthetic fibres in a comprehensive way. The chapter Synthetic Fibres and Plastics begins with an introduction on fibres and lists few commonly known natural and artificial fibres. Apart from this, it also covers different types of synthetic fibres like -

  • Rayon

  • Nylon

  • Polyester and acrylic

Each one of them is explained with the help of activities and figures.

In the next part of the chapter, Synthetic Fibres and Plastics, the characteristics of synthetic fibres are covered thoroughly along with examples.

Moreover, the chapter discusses various aspects of plastics in a detailed manner. Terms like thermoplastic and thermosetting are also defined in the chapter, Synthetic Fibres and Plastics. The uses of thermoplastics are mentioned in the chapter, Synthetic Fibres and Plastics. The characteristic properties of plastics are explained thoroughly under the following labels:

  • Plastic is non-reactive

  • Plastic is light, strong and durable

  • Plastics are poor conductors

Furthermore, the effect of plastic on the environment is explained along with its consequences in the chapter, Synthetic Fibres and Plastics. The information on the type of waste material and the time it takes to degenerate is presented in tabular form. Emphasis is laid on the 4 R principle of reduce, reuse, recycle and recover so as to beat plastic pollution.

The following sections are covered in the chapter, Synthetic Fibres and Plastics -

3.1 What are Synthetic Fibres?
3.2 Types of Synthetic Fibres
3.3 Characteristics of Synthetic Fibres
3.4 Plastics
3.5 Plastics as Materials of Choice
3.6 Plastics and the Environment

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Question 1:

Explain why some fibres are called synthetic.

Answer:

There are some fibres that are prepared by man by using chemicals. These are called synthetic fibres. These are made of small units that join together to form long chains. Examples of synthetic fibres are rayon, nylon, polyester, acrylic, etc.

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Question 2:

Mark (&mnTick;) 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.

Answer:

Rayon is different from synthetic fibres because

(a) it has a silk-like appearance.

(b) it is obtained from wood pulp. (correct)

(c) its fibres can also be woven like those of natural fibres.

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Question 3:

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 _______ __.

Answer:

(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__.

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Question 4:

Give examples which indicate that nylon fibres are very strong.

Answer:

Nylon fibres are very strong. It is used for making ropes used for climbing rocks and for making parachutes. Their usage shows that nylon fibres have high tensile strength.

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Question 5:

Explain why plastic containers are favoured for storing food.

Answer:

The characteristics that make plastics favourable for storing food items are:

(i) Light weight

(ii) Lower price

(iii) Good strength

(iv) Easy handling

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Question 6:

Explain the difference between thermoplastic and thermosetting plastics.

Answer:

There are two types of plastics: Thermosetting plastics and Thermoplastics.

Thermosetting plastic

Thermoplastic

Thermosetting plastic cannot be bent easily. It may break when forced to bend.

Thermoplastic can be bent easily.

Thermosetting plastic cannot be softened by heating. Thus, it cannot be reshaped once moulded.

Thermoplastic can be softened easily by heating. Thus, it can be reshaped.

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Question 7:

Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Answer:

(a) Saucepan handles are made of thermosetting plastics because these plastics do not get softened on heating. Also, thermosetting plastics such as bakelite are poor conductors of heat.

(b) Thermosetting plastics such as bakelite are poor conductors of heat and electricity. Therefore, they are used for making electric plugs, switches, plug boards, etc.

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Question 8:

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.

Answer:

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

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Question 9:

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

Answer:

Rana should buy shirts made from cotton. This is because cotton is a good absorber of water. It can soak the sweat coming out of our body and expose it to the environment. Thus, it helps in evaporating the liquid (sweat), thereby cooling our body.

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Question 10:

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

Answer:

Plastics are not corroded even if they come in contact with strong chemicals. This is because of their non-reactive nature with most materials. For example, the cleansing chemicals that we use at home are stored in plastic bottles, instead of metal containers.

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Question 11:

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

Answer:

No. The handle and bristles of a tooth brush should be made of different materials. The handle of a toothbrush should be hard and strong, while the bristles should be soft and flexible.

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Question 12:

‘Avoid plastics as far as possible’. Comment on this advice.

Answer:

Plastics are non-biodegradable. Once introduced into the environment, they take several years to decompose. Plastics add to the environmental pollution. They cannot be burnt as when burnt, they release poisonous gases. Plastic bags thrown in the garbage dump are swallowed by animals like cows. These plastic bags choke their respiratory system and can even prove fatal. Therefore, we should avoid plastics as far as possible.



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Question 13:

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

Answer:

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

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Question 14:

‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Answer:

Raw materials for natural fibres are mainly derived from plants and this means cutting a lot of trees. This leads to deforestation. But raw materials of synthetic materials are mainly petrochemicals. Hence, manufacturing synthetic fibres helps in the conservation of forests.

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Question 15:

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

Answer:

We will design a circuit to see that thermoplastics are poor conductors of electricity. We need a bulb, some wires, a battery, a piece of metal, and a plastic pipe. Set up the circuit first with the metal and then with the plastic pipe (as shown in the figure). After you switch on the current, 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.

 



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