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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.
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:
See Video:
All clothing material called fabric is woven out of fibres.
There are two types of fibers which can be carized on the basis of their origin and that are written as follows:
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.
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This includes the following fibres-
Cotton is used in the manufacturing of bedsheets and usually used in summers as it keeps us ventilated.
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:
The properties of synthetic fibres are as follows-
It means that synthetic fiber dries easily after washing.
It means that they can be used for a longer period of time.
There are different kinds of synthetic fibers which are as follows-
It is obtained from wood pulp and this pulp is further processed to form rayon. It is also called artificial silk.
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.
Rayon is mixed with cotton to make bedsheets or mixed with wool to make carpets.
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.
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.
Acrylic is an artificial wool. These are synthetic fibers made from a polymer called polyacrylonitrile.
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.
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.
There are two types of plastics which are written below:
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.
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.
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.
The disadvantages of plastics are as follows –
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 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.
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.
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
By this method, we will observe the water absorbing tendency of 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:
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:
Question: How is rayon different from synthetic fibers?
Answer: 2. It is obtained from wood pulp.
Question: Fill in the blanks with appropriate words:
Answer:
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:
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
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