Class 8 Science chapter 3 Synthetic and Man Made fibres

Synthetic Fibres and Plastics

Types of Fibres

There are two types of fibre – One which are obtained from natural sources and other which are man-made.
Fibres which are obtained from natural sources are called natural fibres. For example – cotton, silk, wool, etc.
Fibres which are man-made are called man-made or synthetic fibres. For example – rayon, nylon, acrylic, etc.

Synthetic Fibres:

Synthetic fibres are small units of chemicals joined together in the form of chain. The chain so formed is called polymer. Polymer is a Greek work in which ‘poly’ means many and ‘mer’ means units. Thus, polymer means ‘made of many units joined together’.

Types of Synthetic Fibres:

Rayon:-

Rayon is sythesied from wood pulp. Rayon resembles silk, so it is also known as artificial silk. Rayon fibre can be dyed in different colours. Rayon is very cheap compared to silk.
Bed sheets, shirts, sarees, and many other clothes are made from rayon.

Nylon:-

Nylon was first commercially synthesized fibre. The production of nylon was started almost simultaneously in New York and London, thus it got its name (NY for New York and Lon for London) as nylon. Nylon is synthesized from coal, water and air. Fibre of nylon is very strong and it also resembles silk.
For the first time, nylon was used in making bristle of toothbrush commercially. After that, it was started used as fabrics.
Nylon is used in making of different types of clothes, ropes, socks, curtains, sleeping bags, parachutes, etc. The fibre of nylon is stronger than a steel wire of same thickness.

Polyester

Polyester is one of the most popular man-made fibres which are used in making clothes. It is made of repeating unit of a chemical called ester. Terylene is one of the most famous types of polyester.
Polyester is used in making different types of apparel; such as shirts, pants, jacket, bedsheets, curtains, sarees, mouse-pad, etc. Polyester is used in making ropes, fabrics for conveyor belt, cushioning and insulating material in pillow, etc.
Fabrics made from polyester fibre are almost wrinkle-free, easy to wash and have shiny appearance. It is the polyester which made the fabric cheaper in India as well as in the whole world.
Terrycot is a fabric made after mixing of terylene and cotton. Polycot, polywool, etc. are other fabrics which are made by the mixing of polyester with other natural fibres.
PET (Polyethylene terepthalate) is very famous term for polyester. Water bottles and many containers (used in kitchen), films, wires, and many other useful products are made using PET (polyester).

Acrylic:

Acrylic is man-made fibre. Since, acrylic resembles wool so it is also known as artificial wool or synthetic wool. Acrylic is cheaper than natural wool and can be dyed in various colour. Thus acrylic is very popular and taking the place of wool today.
Acrylic is used in making sweaters, blanket, and other many clothes.

Characteristic of Synthetic Fibre

• Synthetic fibres are cheaper than natural fibre.
• Synthetic fibres are stronger than natural fibre.
• Synthetic fibres are more durable than natural fibre.
• It is easy to maintain the synthetic fibres.
• It is easy to wash the synthetic fabrics.
• Synthetic fabrics are dried up in less time.
• Synthetic fibres are readily available.

Plastics

Plastic is also a polymer. Units of some plastics have linear arrangement while some plastics are formed by the cross linked arrangement of their units.
Plastic can be mould in all types of possible shapes. Plastic can be recycled, coloured, reused, mould or drawn into wires. Thus, plastic is used in making toys, suitcase, bags, cabinets, brush, chairs, tables, and many other countless items. Polythene is one of the most famous types of plastic, which is used in manufacturing of carry bags.
Types of Plastic: Plastic can be divided into two main types – Thermoplastics and Thermosetting.
Thermoplastic: Plastics which can be easily bent or deform on heating are known as thermoplastic. PVC and Polythene are the examples of thermoplastics. Thermoplastics are used in making toys, bottles, combs, containers, etc.
Thermosetting plastic: Plastics which do not get deformed or softened on heating when mold once, are called thermosetting plastics. Bakelite and melamine are the examples of thermosetting plastics. Thermosetting plastics are used in making hard board, electric switch, handles of electrical appliances, handles of kitchen utensils, floor tiles, etc.
Melamine is poor conductor of heat and resists fire, thus it is used in making floor tiles, kitchen materials, etc.
Bakelite is poor conductor of electricity and heat, thus it is used in making electrical switches, and other electrical appliances.

Plastic as a material of choice:

Characteristics of Plastic

Poor conductor – Plastic is a poor conductor of heat and electricity. This makes it suitable to make the covering of electric wires, handles of electrical appliances, handles of utensils, kitchenware, floor tiles, etc.
Plastic is non-reactive: Plastic does not react with air and water and with many of the chemicals. Since, plastic does not react with air and water hence it does not get rusted like iron. This character makes plastic suitable for making of container, water tank, water bottle, plastic pipes, taps, chair, table and other many types of furniture.
Plastic is strong and durable: Plastics are light weight, durable, cheap and very strong. These qualities of plastic made it the need of today. Whether it is polythene bags or pencil box, water bottle or umbrella, furniture or air craft, the use of plastic can be seen everywhere.

Biodegradable and Non-biodegradable:

Substances which get decomposed through the natural processes, such as action of bacteria, etc. are called biodegradable substances. For example; potato peels, peels of other vegetable, food stuffs, fruit, paper, cotton cloths, wood, etc.
Substances which either do not decompose or take many years to get decomposed through the natural process, are called non-biodegradable substance, e.g. tin, aluminium, plastics, etc.

Plastic and the Environment:

Plastic is a non-biodegradable substance. If it is left or thrown, it takes many years to get decomposed or either does not get decomposed. The non-biodegradable nature of plastic has made it a very major problem for environment.

Problems:

Plastic has become very popular and is being used for many purposes. As a result, we are generating a large amount of plastic waste. Since plastic is non-biodegradable, so plastic waste is getting accumulated around us. Disposal of plastic waste is a major concern as it cannot be even burnt. Burning the plastic can result in release of many harmful gases in the atmosphere. This can lead to air pollution.

Preventive measures:

For dealing with the menace of plastic waste, we need to follow the three Rs, i.e. Reduce, Reuse and Recycle.
Reduce: We should reduce the use of plastic. For examples; instead of using plastic bags, we should use cloth or jute bag for shopping.
Reuse: We should reuse some plastic containers, whenever possible. For example; empty bottles and jars can be used for keeping other items in the home and kitchen.
Recycle: Thermoplastic can be recycled. So, items made of thermoplastic should be sent to the recycling industry. Toys, buckets, mugs, etc. are made from thermoplastic

Synthetic Fibres and Platstics

NCERT Solution

Question: 1. Explain why some fibres are called synthetic.

Answer:- Some fibres are made in factories and hence they are called synthetic.

Question: 2. 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: (b) It is obtained from wood pulp

Question: 3. Fill in the blanks with appropriate words:
(a) Synthetic fibres are also called ______ or _______ fibres.

Answer: man-made or artificial

(b) Synthetic fibres are synthesised from raw material called ________.

Answer: petrochemicals

(c) Like synthetic fibres, plastic is also a __________ .

Answer:- polymer

Question: 4. Give examples which indicate that nylon fibres are very strong.

Answer: Nylon is used in making ropes which are used for heavy-duty purposes; like mountaineering and in parachute. These examples show that nylon fibres are very strong.

Question: 5. Explain why plastic containers are favoured for storing food.

Answer: Plastic is a non-reactive and non-corroding material. So, plastic containers do not change the flavour or quality of food. Due to this, plastic containers are favoured for storing food.

Question: 6. Explain the difference between the thermoplastic and thermosetting plastics.

Answer: The shape of thermoplastic can be easily changed by heating again, while the shape of thermosetting plastic cannot be altered once it has been mould into a particular shape. Thermoplastic is used in making toys, combs, containers, etc. Thermosetting plastic is used for making those items which need to withstand high temperature; such as handles of cooking utensils.

Question: 7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles

Answer: Saucepan handles have to withstand high temperature during cooking and thermosetting plastic is ideal for that.

(b) Electric plugs/switches/plug boards

Answer: Electric plugs/switches/plug-boards need to be durable and should withstand continuous use over many years. Moreover, in case of some heating due electric current; they should not melt. Hence, these devices are made from thermosetting plastic.

Question: 8. Categorise 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:

• Can be recycled: Plastic toys, carry bags, ball point pens, plastic bowls, , plastic covering on electrical wires, plastic chairs
• Cannot be recycled: Telephone instruments, cooker handles, electrical switches

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: Cotton has better absorbent property than synthetic fibre. During summer, cotton cloth can absorb sweat. The sweat would give cooling effect to the body, due to evaporation. Thus a cotton shirt would be much more comfortable than a shirt made from synthetic fibre. Hence, Rana should buy cotton shirts for summer.

Question: 10. Give examples to show that plastics are noncorrosive in nature.

Answer: Pickles usually come packed in plastic sachets or glass bottles. Pickles contain acids, yet no harm is done to the plastic sachet. Sanitary cleaners and some acids; which are used as bathroom cleaner are sold in plastic bottles. These examples show non-corrosive nature of plastic.

Question: 11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Answer: The handle and bristles of a tooth brush should be made of different materials. The material which is used for making toothbrush handle should be hard and flexible; because the handle has to withstand lot of stress and has to reach every corner of mouth. The material which is used for making bristles should be soft, flexible yet durable; because the bristles should not damage the tooth or gum but should last longer.

Question: 12. ‘Avoid plastics as far as possible’. Comment on this advice.

Answer: Plastic has gained popularity because of its versatile nature. But because of its unmatched popularity; in terms of variety of usage; it has turned into a curse as well. We are creating too much of plastic waste around us. Plastic is non-biodegradable and many forms of plastic cannot be recycled. This is creating a burden on the environment around us. Hence, the statement, “Avoid plastics as far as possible” is a correct statement.

Question: 13. Match the terms of column I correctly with the phrases given in column II.
Question: 14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Answer: Forests provide many important raw materials from which we make various useful items. Many things which were earlier made from forest produce are now being made from synthetic fibres. For example; plastic chairs have replaced wooden chairs in a big way. Similarly, wooden cartons and crates have been replaced by plastic cartons and crates. The way plastic has replaced wood from many items, it is definitely minimizing the need to cut forests. Thus, it can be said that manufacturing synthetic fibres is actually helping conservation of forests.

Question: 15. Describe an activity to show that thermoplastic is a poor conductor of electricity.

Answer: For this, take a discarded plastic toy, a torch which is in working order. Switch the torch on to check that it is in working condition. From the plastic toy, cut a small piece about the size of a coin. Now insert this coin between two cells of the torch. Then tighten the lid of the torch. Now, switch on the torch. You will notice that the bulb does not glow. This happens because the plastic coin; between two cells; does not allow current to pass between two cells. This shows that thermoplastic is a poor conductor of electricity.