Synthetic Fibres and Plastics Class 8 Notes NCERT and MCQs

23-08-2023 17:12 PM IST Yadvendra Singh

Clothes are made of fabrics that are made from fibres. These fibres can be obtained from natural sources or can be made artificially. The chapter describes synthetic fibres, their composition, advantages, disadvantages and types. It also discusses plastics, their types, uses, and disposal.

What are Synthetic fibres?

Whereas natural fibres like cotton, wool, silk, etc., are obtained from plants or animals, synthetic fibres are made by human beings.  They are also known as man-made fibres. They are obtained by chemical processing of petrochemicals.

Composition of Synthetic fibres: Synthetic fibres, like natural fibres, are made of very large units called polymers. Polymers are made up of many smaller repeating units. They occur in natural fibres also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.

Advantages and Disadvantages of synthetic fibres

Advantages: Synthetic fibres are more durable and affordable which makes them more popular than natural fibres. These do not shrink and require very less or no ironing. They do not absorb water and are dried quickly. Clothes made from synthetic fibres are less expensive in comparison to that made from natural fibres. They are readily available and easy to maintain.

Disadvantages: Their major disadvantage is that they melt on heating and stick to the body of person wearing them after catching fire. These do not absorb sweat making them uncomfortable to wear sometimes. These are non-biodegradable.

Types of synthetic fibres (man-made fibres)

  • Rayon (artificial silk): It was obtained towards the end of nineteenth century by chemical treatment of wood pulp. It is the first synthetic fibre. It has properties similar to silk, a natural fibre obtained from silkworms and discovered in China. It is cheaper than silk and can be woven like silk fibres.
    • Uses of Rayon: It is blended with cotton to make clothing materials and bedsheets. Rayon is blended with wool to make carpets.
  • Nylon:  Made in 1931 without using any natural raw material (from plant or animal), it was the first fully synthetic fibre. It was prepared from coal, water and air. A nylon thread is actually stronger than a steel wire. It is strong, elastic, light, lustrous and easy to wash.
    • Uses of Nylon: It is used in making socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains, etc. It is also used for making parachutes and ropes for rock climbing.
  • Polyester: Fabric made from this fibre does not get wrinkled easily and Terylene is a popular polyester. PET (polyethylene terephthalate) is a very familiar form of polyester.
    • Uses of Polyester: It is used for making bottles, utensils, films, wires etc. This fabric is suitable for making dress material.

NOTE:

Polyester (Poly+ester) is made up of the repeating units of a chemical called an ester.

Esters are the chemicals that give fruits their smell.

Fabrics like polycot, polywool, terrycot, etc. are made by mixing two types of fibres. Polycot is a mixture of polyester and cotton. Similarly, Polywool is a mixture of polyester and wool.

  • Acrylic: The wool obtained from natural sources is quite expensive, whereas clothes made from acrylic are relatively cheap. This fabric is used in making sweaters and winter blankets.

Plastics

Plastics are also polymers like the synthetic fibre. All plastics do not have the same type of arrangement of units. It may be linear or cross-linked. Plastics are easily mouldable i.e. can be shaped in any form. Plastics can be recycled, reused, coloured, melted, rolled into sheets or made into wires. Polythene (Poly+ethene) is an example of a plastic.

Characteristic Properties of plastics

In our day to day life, we use plastic containers for storing food items, water, milk, pickles, etc, as plastic is lightweight, inexpensive, has good strength and can be handled easily. The following are the characteristic properties of plastics:

  • Plastics are nonreactive.  Plastics do not react with water and air and hence, are not corroded easily like some metals. Therefore, chemicals are also stored in plastic containers.
  • Plastics are light, strong and durable. Plastics are generally cheaper than metals.
  • Plastics are poor conductors of heat and electricity. That is the reason why electric wires are covered with plastic. For the same reason, handles of frying pan and screw drivers are also made of plastic.

Plastics are widely used in the healthcare industry. For example- packaging of tablets, threads used for stitching wounds, syringes, doctors’ gloves and a number of medical instruments. Special plastic cookware is used in microwave ovens for cooking food.

Types of plastics

Types of plastics, their examples and uses are summarized below.

Comparison between Thermoplastics and Thermosetting plastics

Thermoplastics

Thermosetting plastics

Plastics which gets deformed easily on heating and can be bent easily are known as thermoplastics.

Thermosetting plastics are plastics which when moulded once, cannot be softened by heating.

Examples: Polythene and PVC

Examples: Bakelite and melamine

Uses: Manufacturing toys, combs and various types of containers

Uses of Bakelite: Making electrical switches, handles of various utensils, etc.

Uses of Melamine: making floor tiles, kitchenware and fabrics which resist fire

 

Some key facts about plastics:

  • Teflon is a special plastic on which oil and water do not stick. It is used for non-stick coating on cookwares.
  • Uniforms of firemen have coating of melamine plastic to make them flame resistant.
  • Bakelite is a poor conductor of heat and electricity.
  • Melamine resists fire and can tolerate heat better than other plastics.

Why disposal of plastics is a problem?

Disposal of plastics is a major problem. Plastics do not get completely burnt easily. On burning, plastics release poisonous gases. On dumping in the ground they may take years to degenerate. This is because of their non-biodegradable nature.

Non-biodegradable and biodegradable material: A material that is not easily decomposed by natural processes is termed non-biodegradable. Tin, Aluminium, other metal cans, Plastic bags are examples of non-biodegradable material.

A material that gets decomposed through natural processes, such as action by bacteria, is called biodegradable. Peels of vegetables and fruits, Paper, cotton cloth, wood, woolen clothes are examples of biodegradable material.

Plastics and environment

Today, life without plastics cannot be imagined. The waste created by plastics is not environment friendly. We need to use plastics in such a manner that we can enjoy their good qualities and at the same time minimize the environmental hazards for the living communities. It is better to recycle plastic waste. Most of the thermoplastics can be recycled. One should follow 4R principle to save the environment- Reduce, Reuse, Recycle and Recover.

MCQs related to NCERT Class 8 Science Chapter 3 Synthetic Fibres and Plastics

1. The properties of Rayon are similar to which of the following natural fibres?

a. Cotton

b. Wool

c. Silk

d. Jute

Ans. c

Explanation:

Rayon is also known as artificial silk. It was obtained towards the end of nineteenth century by chemical treatment of wood pulp. It has properties similar to silk.

2. Which of the following artificial fibres was the first fully synthetic fibre?

a. Rayon

b. Nylon

c. Polyester

d. Acrylic

Ans. b

Explanation:

Nylon was made in 1931 without using any natural raw material (from plant or animal). It was the first fully synthetic fibre. It was prepared from coal, water and air.

3. Which of the following plastics is/are an example of thermoplastics?

a. Polythene

b. PVC

c. Bakelite

d. Both a and b

Ans. d

Explanation:

Polythene and PVC are examples of thermoplastics. They get deformed easily on heating and can be bent easily.

4. Which of the following plastic is used for non-stick coating on cookwares?

a. PVC

b. Teflon

c. Bakelite

d. Melamine

Ans. b

Explanation:

Teflon is a special plastic on which oil and water do not stick. It is used for non-stick coating on cookwares.

5. 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.

d. None of the above

Ans. b

Explanation:

Rayon has properties similar to silk but what makes it different from synthetic fibres is that it is obtained from a natural source- wood pulp after treating it chemically.

NCERT Class 8 Science Chapters
Chapter 1 Crop Production and Management Notes
Chapter 2 Microorganisms: Friend and Foe Notes

 

 

Frequently Asked Questions (FAQs) about Synthetic Fibres and Plastics

What are synthetics fibres?

The man made fibres are called synthetic fibres.

What are the examples of Synthetic fibres?

Rayon, Nylon, Polyester, Acrylic are the examples of Synthetic fibres.

What are the disadvantages of Synthetic fibres?

The disadvantage of synthetic fibres is that they melt on heating and stick to the body of person wearing them after catching fire. These do not absorb sweat. These are non-biodegradable.

What are the examples of thermoplastics?

Polythene and PVC are examples of thermoplastics.
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