Synthetic Fibres and Plastics

CBSE Class 8 - Science - Synthetic Fibres and Plastics

Synthetic Fibres and Plastics

NCERT Chapter Solutions and Q & A

Q1: Explain why some fibres are called synthetic?

Answer: Some fibres are called synthetic because they are not made from natural fibres. Instead, they are made by chemical processing of petrochemicals. The synthetic fibres are made up of very large units called polymers. Some of the synthetic fibres are: rayon, nylon and acrylon.

Q2: 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

Answer: (b) it is obtained from wood pulp

Q3: Fill in the blanks with appropriate words:

Answer:

(a) Synthetic fibres are also called man-made or artificial fibres.

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

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

Q4: Give examples which indicate that nylon fibres are very strong.

Answer: Nylon is a very strong fibre that is why nylon is used for making parachutes, rock climbing ropes, fishing nets seat belts etc. A nylon thread is actually stronger than a steel wire.

Q5: Explain why plastic containers are favoured for storing food.

Answer: Plastic containers are favoured for storing food for the following reasons:

1.            Plastic containers are light weight so they are easy to handle.

2.            The price of plastic containers is very less as compared to other containers.

3.            They have good strength.

4.            Plastic containers are durable.

Q6.Explain the difference between the thermoplastic and thermosetting plastics.

Answer:

	Thermoplastics	Thermosetting plastics
1	Plasticcs which can be deformed and bend easily on heating are known as thermoplastics.	Plastics which when moulded once cannot be bent and deformed on heating are known thermosetting plastics
2	They are used for making toys, containers, etc	They are used for making switches, handles of utelsils, floor tiles etc.
3	Example: PVC, Polythene	Bakelite and Melamine

Q7.Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Answer:  

(a) Saucepan handles: Saucepan handles are made from thermosetting plastics because these are bad conductors of heat and electricity. They do not bend or deform on heating.

(b) Electric plugs/switches/plug boards: Electric plugs/switches/plug boards etc. are made up of thermosetting plastics because thermosetting plastics are bad conductors of heat and electricity. It does not allow the current to pass through it.

Q8: 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	Cannot be recycled
1	Plastic toys carry bags ball point pens plastic chairs plastic covering on electrical wires, plastic bowls	cooker handles electrical switches telephone instruments

Q9: 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 is advised to buy a cotton shirt for summers because cotton absorbs the sweat and the pores in cotton allows easy evaporation and keeps our body cool, whereas synthetic shirts don’t absorb sweat and they are very uncomfortable to wear in summers.

Q10: Give examples to show that plastics are noncorrosive in nature.

Answer:

1.            We can store various kinds of chemicals and other materials in plastic containers because they are non-reactive and does not react with water and air.

2.            Teflon, a kind of plastic is used as a coating to manufacture non-stick cookwares.

3.            Melamine is used for making floor tiles and kitchenware.

4.            Bakelite is a poor conductor of heat and electricity so it is used for making electric switches and handles of the utensils.

Q11: Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Answer:

The bristles of a tooth brush should be made of soft material so that it does not harm the gums and the handle should be made of hard material so that it can give a firm grip. Therefore, the bristles are made up of nylon fibres which are strong, elastic, lustrous, light weight and easy to handle and the handle is made of hard plastic as it is strong, durable, poor conductor of heat and electricity.

Q12: "Avoid plastics as far as possible". Comment on this advice.

Answer:

Although plastics have become important in our daily life, we should avoid them as far as possible. 

1.            Plastics are non-biodegradable and take a lot of time to decompose. 

2.            Plastics are not eco-friendly. By burning plastics, poisonous fumes are released that cause air pollution. 

3.            Sometimes cows and other animals may eat plastics present in the garbage which may choke their respiratory system and even cause death. 

4.            The plastic left in the soil results in soil pollution. 

5.            Plastic bags drained into the water bodies cause threat to the aquatic life also. 

6.            Polybags choke the drains and sewage pipes thus causing lot of trouble. 

So we should use plastic judiciously and give preference to other alternatives like jute bags etc. 

Q13: Match the terms of column I correctly with the phrases given in column II.

	Column I	Column II
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 cookwares
iv	Nylon	(d) Fabrics do not wrinkle easily

Answer: i-d, ii-c, iii-a, iv-b

Q14: Explain, ‘Manufacturing synthetic fibres is actually helping conservation of forests’.

Answer: 'Manufacturing synthetic fibres is actually helping conservation of forests’ because synthetic fibres are man-made fibres. These fibres are made from petrochemicals. For manufacturing synthetic fibres cutting of trees or killing of animals is not required and hence we conserve our natural environment.

Q15: Describe an activity to show that thermoplastic is a poor conductor of electricity.

Answer: Take a small piece of thermoplastic material and connect it as shown in the figure When we close the switch, no current passes and the bulb does not glow.

Q16: Terylene is used in making ...

(a) Dressing material

(b) Food packaging

(c) Non-sticky utensils

(d) All of the above.

Answer: (a) Dressing material

Q17: What are polymers? 

Answer:  Many small chemical units (called macro molecules) combine to form a large unit. Polymer is made up of such repeating units.

Q18: What is the polymer unit of cotton?

Answer: Cellulose.

Q19: What type of polymer units arrangement are found in plastics?

Answer: In general two types:  

·                     Linear arrangement

·                     Cross-linker arrangement

Q20: Give examples of (a) natural fibres (b) semi-synthetic fibres and (c) synthetic fibres

Answer:

(a) Natural fibres: Cotton, silk, jute

(b) Semi-synthetic fibres: Rayon

(c) Synthetic fibres: PVC, Nylon, Terylene, Teflon

Q21: What is full form of PVC and PET

Answer:  PVC: Polyvinyl Chloride

                PET: Polyethylene tetrapthalate

Q22:  Name the R's in 4R principle.

Answer: Reduce, Reuse, Recycle and Recover.

MAIN POINTS

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 thermoplastics.