Synthetic fibres and Plastics Class 8 Notes, Question Answers

Synthetic Fibres and Plastics Class 8 Science Chapter 3 as per NCERT Book used in CBSE and other Schools. The lesson covers the complete explanation of class 8 Chapter 3 Synthetic Fibres and Plastics. Topics covered are Introduction to fibres, kinds of fibres. Different types of synthetic fibres like, Rayon fibres, Nylon fibres, Polyester fibres and Acrylic fibres have been explained. The lesson also covers Plastic- Its types and its advantages and disadvantages. The lesson covers all important questions based on Synthetic Fibres and Plastics. NCERT solutions to book questions have also been provided for ease to the students.

Natural fibres	polyester	Thermosetting plastics
Synthetic fibres	acrylic	disadvantages of plastics
Rayon	plastics	Biodegradable and non biodegardable substances
Nylon	Thermoplastics	steps to save environment

 

As we all know that there are different materials present in our surroundings and these materials are used for different purposes as per our need. For example: Plastic, polybags, clothes. There are different types of clothes, some of which have shiny appearance; some of them have different textures. All these clothes are made up of fibers and clothing material totally depends upon the nature of fiber. Polythenes are made up of plastic. Cold drink glass is also made up of plastic. In this chapter we will discuss about fibers and plastics in detail.

The topics we will cover in this chapter are as follows:

1. Introduction of fibres
2. Kind of synthetic fibres
3. Rayon fibres
4. Nylon fibres
5. Polyester fibres
6. Acrylic fibres
7. Plastic, Its types and its advantages and disadvantages.

See Video:

 

What is Fibre?

All clothing material called fabric is woven out of fibres.

Types of fibers:

There are two types of fibers which can be carized on the basis of their origin and that are written as follows:

1. Natural fibers
2. Synthetic fibers

Natural fibers

Natural fibers are obtained from plant and animal sources. They occur in ready to use form. There are certain fibers which are obtained from plants and are known as vegetable fibers.

This includes the following fibres-

1. Protein fibers like (wool and silk)
2. Cellulose fibers (like cotton and linen).

Cotton is used in the manufacturing of bedsheets and usually used in summers as it keeps us ventilated.

1. Mineral fiber (like asbestos). This is helpful in the manufacturing of mats or carpets that are used at home for decoration.

Synthetic fibers

These are also known as man-made fibers. Synthetic fibers are obtained by chemical processing of petrochemicals. The synthetic fibers can be woven into a fabric, just like natural fiber. Synthetic fibers have a wide range of use ranging from household articles like ropes, buckets, furniture, containers, etc. to highly specialized uses in aircrafts, ships, spacecrafts, health care, etc.

Synthetic fibers and plastics are made up of molecules called polymers. A polymer is a large molecule formed by combination of many small molecules, each of which is called a monomer.

The structure of polymer can be compared to that of a bead necklace- the bead being the monomers. The process of combining the monomers to form a polymer is called polymerization.

These are man-made fibers that come from chemical resources.

They are continuous filament fibers.

They consist of multiple units that join together to form big molecules called polymer.

They are manufactured using plant materials and minerals.

For example: Viscose comes from pine trees. Acrylic, nylon, polyester come from oil and coal. Viscose is processed to form rayon.

See Video:

Properties of synthetic fibers

The properties of synthetic fibres are as follows-

1. They quickly dry up.

It means that synthetic fiber dries easily after washing.

1. They are durable.

It means that they can be used for a longer period of time.

1. They are less expensive.
2. They are readily available.
3. They are easy to maintain and do not need extra care.

Kinds of Synthetic Fibers

There are different kinds of synthetic fibers which are as follows-

1. Rayon
2. Polyester
3. Nylon
4. Acrylic
5. Plastic

Rayon

It is obtained from wood pulp and this pulp is further processed to form rayon. It is also called artificial silk.

Properties of Rayon

It is semi synthetic fiber as wood pulp is used for its manufacturing.

It is manufactured regenerated cellulose fiber.

It is also called as viscose rayon and artificial silk. The liquid obtained from the pine tree is called as viscose and it has lustre due to which it is also called viscose rayon and artificial silk.

Properties of Rayon

1. It is versatile fiber and widely used.

Rayon is mixed with cotton to make bedsheets or mixed with wool to make carpets.

1. It has comfort providing properties.
2. They can be easily dyed as per our needs.
3. It is soft, smooth, cool, comfortable, and highly absorbent.
4. They do not insulate body heat. Therefore, it is used in hot and humid climates.

Uses of Rayon

Rayon is used in textile industry for making shirts, skirts etc.

This fabric has gained unfair reputation as it is constantly used in making cheap garments that have very low price. These cheap garments are made up of rayon.

Nylon

1. It is made from coal, water and air.
2. It is the first fully synthetic fiber which was made in 1931.
3. It is widely found.
4. It has ability to be lustrous, semi lustrous or non lustrous.
5. It is durable as it has high tenacity or strength.
6. It has excellent abrasion resistance. It means not extra care is required. It is rough and tough type of fiber.
7. It is heat resistant.
8. It is highly resistant to insects, fungi, animals, chemicals, etc.

Uses OF Nylon

1. As we know that nylon has high strength. Due to this property, it is used for making fishing nets, parachute, bag, ropes etc.
2. It is used for making fabrics.
3. It is used in the manufacturing of various machine parts.
4. It is often blended with wool to increase the strength.

Polyester

Polyester is manufactured from petroleum. It is a category of polymer which contain an ester group in their main chain. PET (Polyethylene terephthalate), the commonly used polyester, is made from two monomers by condensation polymerization.

This PET is used in the manufacturing of pet bottles like cold drink, water bottles.

 

Properties of Polyester

1. It is very strong
2. It is very durable, resistant to chemicals. Polyester does not shrink.
3. It is hydrophobic in nature and dries up quickly as it does not absorb water.
4. It retains its shape.
5. It is easily washed and dried.

Uses

1. It is used to make polyester suits.
2. It is used in the manufacturing of ropes in industries. Then these ropes are useful in rock climbing etc.
3. Pet bottles are also commonly used.
4. Example of polyester: polyester Mat and polyester rope.

Acrylic

Acrylic is an artificial wool. These are synthetic fibers made from a polymer called polyacrylonitrile.

Properties of Acrylic

1. It is warm and lightweight.
2. It is soft and flexible.
3. It is resistant to moths and chemicals.
4. It gives wool like feel.
5. It does not shrink and is wrinkle- resistant.
6. It is cheaper than wool.
7. It can also be dyed very well in a variety of color.

Uses of acrylic

1. Acrylic fiber is often used for making sweaters, blankets, cashmere, jackets, shawls, and tracksuits.
2. It is also used as linings for boots and gloves as well as in furnishing fabrics and carpets.
3. It is used in craft yarns, boat sails and vehicle covers.

Question: What is the chemical nature of polyester? What are polycot and polywool?

Answer: Polyester is actually made by repeating the units of a chemical called ester. Esters are the chemicals which give characteristics smell like fruits. Fabrics are sold by names like polycot, polywool, terrycot etc. As the name suggests, these are made by mixing two types of fibers. Polycot is a mixture of polyester and cotton. Polywool is a Mixture of polyester and wool.

Plastic

The word ‘plastic’ comes from greek word “plastikos” that means “to form”. Plastic is made from petroleum and natural gas.

Plastics can be easily molded into any shape and sizes. Plastic is also defined as a material that can be heated and molded in any shape after cooling. For example: Polythene. Plastics can be recycled, reused, colored melted, rolled into sheets or made into wires. Some of the plastic has linear arrangement, while some has cross linked.

Properties of Plastic

1. It is lightweight.
2. It does not rust.
3. It is easy to handle.
4. It is reusable.
5. It is non reactive.
6. They are poor conductors of heat and electricity.

Example of Plastics

1. Toys
2. Plastic Chairs

Types of plastics

There are two types of plastics which are written below:

1. Thermoplastics
2. Thermosetting plastics

Thermoplastics

Thermoplastic is a plastic which gets deformed easily on heating and can be bent easily. On heating thermoplastics, there is no chemical change. For example: Polythene, polytetrafluroethylene (PTFE), polystyrene, and PVC (polyvinylchloride). These are used for manufacturing toys, combs, car grills and various types of containers.

Thermosetting plastics

There are some plastics which when molded once cannot be softened by heating again and again. These are called thermosetting plastics. For example: Bakelite and melamine. Bakelite is used for making electrical switches, handles of various utensils etc. Melamine is used for making floor tiles, kitchenware etc.

Uses

1. It is used in making bottles.
2. It is used in making plastic toys.
3. It is used for packaging many goods like container etc.

 

Question: What is the name of plastic that is used in making non stick pans?

Answer: Teflon is used in making non stick pans because oil and water does not stick on it.

Question: Why polyester is quite suitable for making dress materials? Name any two types of polyesters and their uses. 

Answer: Fabric made from polyester does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material. Terylene is a type of popular polyester. It can be drawn into very fine fibers that can be woven like any other yarn.
PET is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

Question: Why is it advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen? 

Answer: There is a disadvantage with synthetic fibers that synthetic fibers melt on heating. If the cloth catches fire it can be very disastrous. The fabric melts and sticks to the body of the person wearing it. It is therefore advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen.
 

Question: By which material is artificial wool formed? Why has artificial wool become more popular than natural wool? 

Answer: Artificial wool is prepared from another type of synthetic fiber called acrylic. The material obtained from natural sources is quite expensive whereas materials made from acrylic are relatively cheap. They are available in a variety of colors. Synthetic fibers are more durable and affordable which makes them more popular than natural fibers. 

Disadvantages of plastic

The disadvantages of plastics are as follows –

1. They have caused many health and environmental hazards.
2. Some monomers of plastics have proven to cause cancer also.
3. Plastics are non- biodegradable and do not decompose for several years.
4. When plastics are burnt, toxic fumes are released into the atmosphere causing pollution.

Biodegradable substances

These are those substances that can be decomposed by microorganisms through natural processes.

Non biodegradable substances

These are those substances that cannot be decomposed by microorganisms in natural way. For example: Plastics.

Types of waste	Approximate time taken to degenerate	Nature of material
Peels of vegetable and fruits, leftover food stuff etc.	It takes 1 to 2 weeks to degenerate.	Biodegradable
Paper	It takes 10-30 days to degenerate.	Biodegradable
Cotton clothes	It takes 2-5 months to degenerate.	Biodegradable
Wood	It takes 10-15 years to degenerate.	Biodegradable
Woolen clothes	It takes About a year to degenerate.	Biodegradable
Tin, Aluminum and other metal cans	It takes 100-500 years to degenerate.	Non- Biodegradable
Plastic bags	It takes several years to degenerate.	Non- Biodegradable

Plastic

Plastic is not environment friendly. Therefore certain steps have to be taken it order to protect our environment. Like polythene, is a non-biodegradable substance which means that microorganisms cannot decompose them.

Steps that are required to protect the environment

1. We should never throw plastic bags or other plastic articles into water bodies, drains or on roads.
2. We should carry cotton or jute bags for shopping.
3. We should buy products with less plastic packaging.
4. We should encourage the people to recycle and reuse plastic.

Time to check knowledge by answering the following questions-

1. Polyester is a long chain polymer of a chemical substance called ____
Answer: Ester

2. What is the name of regenerated synthetic fiber?
Answer: Rayon

3. What is the name of first fully synthetic fiber?

Answer: Rayon

4. Give an example of natural polymer?
Answer: Cellulose

5. What is the full form of PVC?
Answer: Poly vinyl Chloride

6. Acrylic fibers are advantageous over?
Answer: Wool

7. Nylon is made from ____?
Answer: Petro chemicals

8. The polymers in which smaller units are linked to each other in straight arrangement are called as _______?
Answer: Thermoplastics

9. Name the plastic which cannot be softened once molded into a shape?
Answer: Thermosetting plastic

10. Name the plastic used for making insulation cover of electrical wires?
Answer: PVC

11. Rayon clothes are comfortable to wear in ____? 
Answer: Summer season

12. The first fully synthetic fiber was _______?
Answer: Nylon

13. The non stick coating on pans and other cooking utensils is made from ______?
Answer: Teflon

Question: Fill in the blanks with correct word-

a. ______ fibers are less expensive than natural fibers. 

b. Synthetic fibers are not good absorbers of _______ . 

c. In______ weather clothes made of synthetic fiber stick to the body. 

d. Synthetic fibers catch fire easily so they are _______ . 

e. Clothes made of synthetic fibers should not be worn in ______

Answers:

a. Synthetic

b. Sweat

c. Hot/humid

d. Inflammable

e. Kitchen/laboratory. 

Question: Fill in the blanks :- 

a. ______ burns vigorously and leaves little ash. 

b. ______ burns slowly with the smell of burning hair. 

c. ______ shrinks on burning producing black smoke.

d. ______ burns readily with the smell of burning paper. 

e. ______ shrinks if burnt and forms a black bead a long with sooty flame. 

 

Answers:

a. cotton

b. Wool

c. Polyester

d. Rayon

e. Acrylic.

Question: Fill in the blanks :- 

a. Rayon is prepared from ______ . 

b. Polythene is prepared from______ . 

c. Nylon is prepared from simple chemicals obtained from ______ . 

d. Polyester is made from ______ products. 

e. ______ is called a regenerated fiber. 

Answers:

a. Cellulose

b. Ethylene

c. Coal

d. Petroleum

e. Rayon.

As a citizen remember 4R’s principle:

Reduce: This means that anything that harms the environment should not be utilized or we should limit the use of that particular substance.

Reuse: This means that we should reuse the substances that does not harm our environment and it should be biodegradable.

Recycle: We should recycle the substances.

Recover: We should recover the substances that are useful for us.

Question: Why has government banned the use of polythene bags ? 
Answer: Polythenes or plastic bags are non biodegradable. It means that they cannot be decomposed or recycled by the microorganisms. Besides this an improper disposal of polythenes leads to following environmental problems: 
1. soil and water pollution. 
2. Blockage and choking of drains and sewer lines . 
3. Death of animals that chew these polythene bags along with any food.

Time to check knowledge by answering the following questions-

Choose the correct option in the following questions: 

01. What is the other name for artificial silk?
          (a) Nylon                                 (b) Rayon
          (c) Acrylic                               (d) Polyester

02. Which fiber is used as artificial wool?
          (a) Acrylic                               (b) Rayon 
          (c) Nylon                                 (d) Cotton

03. Polymers are made up of small units called _____
          (a) layers                                 (b) molecules
          (c) cells                                   (d) monomers

04. The strongest synthetic fiber is ______
         (a) nylon                                  (b) rayon
         (c) polyester                            (d) acrylic

05. Wood pulp is used to make ______
         (a) plastic                                (b) wool
         (c) jute                                    (d) rayo

06. Which of the following is a natural fiber?
         (a) Wool                                 (b) Nylon
         (c) PVC                                  (d) Polythene

07. Melamine is ______
         (a) thermoplastic polymer     (b) thermosetting polymer
         (c) fibre                                  (d) elastomer

08. Fiber produced in factories is called ______
         (a) man-made fibre               (b) natural fibre
         (c) synthetic fibre                  (d) both (a) and (c)

09. PET is a ______
         (a) polyester                           (b) polyamide
         (c) nylon                                (d) thermosetting polymer

10. Which of the following cannot be recycled?
         (a) Toys                                 (b) Cooker handles
         (c) Carry bags                       (d) Plastic chair

11. Synthetic fibers synthesized from raw materials are called _____
         (a) jute                                  (b) rayon
         (c) petrochemicals                (d) Bakelite

12. Bakelite is an example of _____
         (a) fibre                               (b) elastomer
         (c) nylon                              (d) thermosetting polymer

13. Which term is used for polymers made up of a large number of glucose units?
         (a) Protein                           (b) Fructose
         (c) Cellulose                        (d) Polyester

14. Which of the following is non-biodegradable?
         (a) Paper                              (b) Cotton cloth
         (c) Wood                             (d) Plastic

15. Which of the following is natural fibre obtained from plants?
        (a) Cotton                           (b) Wool
        (c) Rayon                            (d) Ketone

Answers

1.  b
2. a
3. d
4. a
5. d
6. a
7. b
8. d
9. a
10. b
11. c
12. d
13. c
14. d
15. a

Let us perform an activity to compare strength of the fibers

1. First, we need to take an iron stand with a clamp.
2. Take a cotton thread of about 60 cm length.
3. Tie it to the clam so that it hangs freely.
4. At the free end suspend a pan so that weights can be placed in it.
5. Add weights one by one till it breaks. Note down the total weight required to break the thread.
6. This weight indicates the strength of the fiber. Repeat the same activity with threads of wool, polyester, silk and nylon.

Compare water absorbing tendency of different fibres

By this method, we will observe the water absorbing tendency of fiber.

1. So, the first step is we need to take two cloth pieces of same size about half a meter square each. One of these fiber should be made from natural fiber (cotton bedsheets). The other fiber should be made up of synthetic fiber (polyester). If in case you are unable to identify the fiber, you can take help of your parents in selecting these pieces.
2. Then, we need to soak the pieces in different mugs and each mug contains the same amount of water.
3. Take the pieces out of the containers after five minutes and spread them in the sun for a few minutes.
4. This shows that synthetic fiber dry quickly as compare to natural fiber.

In this way, we can find out the water absorbing tendency of different fibers.

Question & Answer

Question: What is the difference between Thermosetting and Thermoplastics?

Answer:

Thermoplastics: These are plastics that easily get deformed on heating and can be bent easily. They are used for making toys, car grills etc. For example: Polyethene and PVC.

Thermosetting plastics: These are those which once molded can’t be softened on heating. They are used in making handles of utensils, floor tiles etc. For example: Bakelite etc.

Question: How can you show that thermoplastics are poor conductors of electricity?

Answer: As you have seen that all electric wires are insulated with plastic. We have seen that those plastic covers do not cause any kind of electric shock when you touch it. Thus, we can say that thermoplastics are poor conductors of electricity.

Question: Write advantages of using plastic containers for storing food?

Answer: The advantages of using plastic containers for storing food are written as below:

1. They do not react with food and prevents the food from spoiling.
2. They are strong and light.
3. They are easy to handle and use

Question: Why do mountaineers use nylon ropes for climbing the mountains?

Answer: mountaineers use nylon ropes for climbing the mountains because nylon is a high strength fiber so it does not break easily. It has capacity to bear weight and helps the mountaineers to climb.

Question: Write properties of nylon.

Answer: Properties of nylon are:

1. It is strong.
2. It is elastic and light
3. It is lustrous and easy to wash

Question: How is rayon different from synthetic fibers?

1. It has a silk like appearance
2. It is obtained from wood pulp
3. Its fibers can also be woven like those of natural fibers

Answer: 2. It is obtained from wood pulp.
 
Question: Fill in the blanks with appropriate words: 

1. Synthetic fibers are also called ……… or …….. fibers.
2. Synthetic fibers are synthesized from raw material called ………..
3. Like synthetic fibers, plastic is also a ………..

Answer:

1. artificial, man-made
2. petrochemicals
3. artificial sources.

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

Answer: Parachutes and ropes for rock climbing which indicates that nylon fibres are strong.
 
Question: Explain why plastic containers are favored for storing food. 

Answer: Three main advantages of using plastic containers for storing food are:

1. They do not react with food items.
2. They do not get rusted.
3. They are light, strong and durable.

Question: Explain why the following are made of thermosetting plastics. 
        (a) Saucepan handles
        (b) Electric plugs/switches/plug boards.
Answer: Above articles are made up of bakelite (a thermosetting plastic) because they are–
(i) poor conductors of electricity
(ii) heat resistant