class-8 science Chapter-1 synthetic fibers and plastics

For students and by students

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STUDY

MATERIAL









CLASS - VIII

SCIENCE

(CHEMISTRY)
SYNTHETIC FIBRES AND PLASTIC

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SYNTHETIC FIBRES AND PLASTICS






All fabrics are materials made from many fibres, which are obtained from natural or
artificial sources. Cotton is a natural fibre obtained from the cotton plant. All
synthetic fibres are man-made fibres that are prepared by a number of processes
using raw material of petroleum origin, called petrochemicals.

Synthetic fibres consists of many small units or monomers combine to form a larger
unit called a polymer. (Pause) Polymer is a Greek word, formed by the combination of
‘poly’ which means many and ‘mer,’ which means part or unit. Thus, a polymer is
made up of many repeating units called monomers.
Example:
Nylon, rayon, acrylic, polyester...etc

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Cotton is a form of polymer called cellulose, which is made of a large number of
glucose units.

Advantages of synthetic fibres:
• Synthetic fibres can be washed and dry quickly.
• They do not wrinkle easily and are very durable.
• They are less expensive when compared to natural fibres.
• They are easy to maintain
• They are readily available than natural fibres.

Disadvanatges of synthetic fibres:
A big disadvantage of synthetic fibres is that they melt on heating.



Synthetic material catches fire, the fabric melts and sticks to the body of the person
wearing it. This is extremely dangerous, so it is important not to wear synthetic
clothes in the kitchen or laboratory.

Rayon:
Fibre obtained by chemically treating wood pulp is called rayon or artificial silk. Rayon
cannot be called a natural fibre as it is man-made.

Characteristics of rayon:
• Rayon is cheaper than silk and can be woven like silk fibres.
• It is highly absorbent, soft and comfortable.
• It is easy to dye in a wide range of colours and drapes well.

Uses of rayon:
• Rayon widely used in all types of clothing and home furnishings.
• Rayon mixed with cotton to make bed sheets and curtains or with wool to
make carpets.

Nylon:
Nylon is a synthetic fibre made from coal, water and air. It is elastic, very lustrous and
easy to wash. It dries quickly and retains its shape.

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Uses of nylon:
• Nylon is used to make seat belts in cars, curtains, sleeping bags, tents, tooth
brushe bristles, socks and ropes,
• It is also used to make parachutes and ropes for rock-climbing.
• It is used to make fishing nets.

Polyester:
Polyester is a synthetic fibre, derived from coal, air, water and petroleum.
Polyester is made of repeating chemical units called esters.
Poly + Ester → Polyester
- ester - ester - ester - ester - ester -
Fabrics which are madeup of polyester can be washed and dried quickly,
Polycot is a mixture of polyester and cotton and polywool is a mixture of polyester and
wool. Fabric made from polyester retains its shape and remains crisp. Polyester is
easy to wash and dry.
Terylene is a popular form of polyester, which can be drawn into very fine fibres.
These fibres can be woven like any other yarn. PET or poly-ethylene terephthalate is
another familiar form of polyester, which is used to make bottles, utensils, films and
wires. Polyester is also used for making hoses, ropes, nets, thread, raincoats, fleece
jackets, clothing and medical textiles.

Acrylic:
Acrylic is a synthetic polymer of methyl methacrylate. Fabric made from acrylic is
warm to wear, retains its shape and is durable.
Acrylic is easy to wash and dries quickly.
Acrylic is used in apparel like sweaters and socks and in home furnishings such as
furniture, carpets, blankets and upholstery fabrics. Industrial uses of acrylic include
craft yarns, awnings, boat and vehicle covers and luggage.

PLASTICS :



Plastics are polymers of long carbon chains. They consist of very long molecules each
composed of carbon atoms linked in chains. Fossil fuels contain hydrocarbons
(compounds containing hydrogen and carbon), which provide the building blocks for
long polymer molecules. These small building blocks, called monomers, link together
to form long carbon chains called polymers. These monomers can be linked in linear
manner to form linear polymers and linked cross linked manner to form cross linked
polymers.

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Depending on this physical property, plastics are categorized into two
types: Thermoplastics and Thermosetting plastics.

Thermoplastics:
Plastics that get deformed easily on heating and can be bent easily are known as
thermoplastics. Most of the linear polymers or combination of linear and cross-linked
polymers are thermoplastics. Example: PVC, polythene, nylon, acrylic, celluloid and
cellulose acetate

Thermosetting plastics:
Plastics which when moulded, cannot be softened by heating are called thermosetting
plastics. Heavily cross linked polymers are the thermosetting plastics.
Example: Bakelite, melamine, vulcanised rubber, duroplast and epoxy resin

Characteristics of plastics:
• Plastics do not corrode easily
• Plastics can carry easily as they are low weight materials.
• Plastics are strong and durable.
• Plastics can be easily moulded into different shapes and sizes.
• Plastics are poor conductors of heat and electricity. Thus used to make
handles of cooking vessels.
Uses of plastics:
Plastic Uses
PVC (poly vinyl
chloride)
Used in food packaging, making of sanitary
pipes
LDPE (Low
density
polyethylene)
Used making of in food bottles and packaging
of foods, polybags
HDPE (High
density
polyethylene)
Used in making food and drink containers
and in making of containers which are used
in laboratory to store chemicals
PET
(polyethylene
terephthalate) Used in beverage bottles and food containers

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Plastic has a wide variety of uses in our day to day life.
HOUSEHOLD APPLIANCES: Special plastic is used in the making of cookware used
in microwave ovens for cooking food. In microwave ovens, the heat cooks the food but
does not affect the plastic vessel.Teflon coating is another plastic which is used in
non-stick cook ware. Teflon is a special plastic on which oil and water do not stick.

HEALTH CARE: The packaging material of tablets, syringes, threads used for
stitching wounds and doctor gloves etc are made of plastics.

TRANSPORTATION: The interior parts of a car like the dash board, and some other
parts of helicopters and aeroplanes are made of plastic.

Biodegradable materials:
Material that gets decomposed through natural processes, such as by the action of
bacteria, is termed as biodegradable.
Example: Peels of vegetables, fruits, other food stuff, paper and pieces of clothes.

Non-biodegradable materials:
Material that is not easily decomposed by natural processes is termed as non-
biodegradable. Example: Plastic, polythene covers, thermocol, etc.
Harmful effects of plastics:
Polythene bags are non-biodegradable and cause environmental pollution. They
undergo a process known as photo degradation, in which they break down into
smaller and smaller toxic particles. These particles contaminate soil and water and
end up entering the food chain when eaten accidentally by animals like cows. In
addition polythene bags can choke cattle to death. Hundreds and thousands of
whales, dolphins, sea turtles and other marine mammals die every year after
consuming discarded polythene bags. Polythene bags are also responsible for the
clogging of drainage systems in cities and towns. Plastics take several years to
decompose.

Ways to reduce the use of plastic materials:
• Reduce- Avoid the use of disposable plastic bags, instead make use of cotton or
jute bags for shopping.
• Reuse: Plastic items should be reused wherever possible.
• Recycle: It is better to recycle plastic waste. Most thermoplastics can be
recycled.

Text Book Questions and Answers

1.Give examples which indicate that nylon fibres are very strong.

Nylon fibres are very strong. It is used for making ropes used for climbing rocks
and for making parachutes. Their usage shows that nylon fibres have high
tensile strength.
2. Explain why some fibers are called synthetic.
Synthetic fibers are prepared by using petro chemicals. These are made
of small units that join together to form long chains.
Examples: Rayon, nylon, polyester, acrylic etc.

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3. Explain why plastic containers are favoured for storing food. (

The characteristics that make plastics favourable for storing food items are:
(i) Light weight

(ii) Lower price
(iii) Good strength

(iv) Easy handling

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

(a) Sauce pan handles
(b) Electric plugs/switches/plug board

(a) Sauce pan handles are made of thermosetting plastics because these plastics
do not get softened on heating.

(b) Thermosetting plastics such as Bakelite are poor conductors of heat
and electricity. Therefore, they are used for making electric plugs,
switches, plug boards etc.

5. Should the handle and bristles of a tooth brush be made of the
Same material? Explain your answer.
No. The handle and bristles of a tooth brush should be made of
different materials. The handle of a toothbrush should be hard and
strong, while the bristles should be soft and flexible

6. Give examples to show that plastics are non-corrosive in nature.
Plastics are not corroded even if they come in contact with strong chemicals.
This is because of their non-reactive nature with most materials. For example,
the cleansing chemicals that we use at home are stored in plastic bottles,
instead of metal containers.

7 .Rana wants to buy shirts for summer. Should he buy cotton shirts or
shirts made from synthetic material? Advise Rana, giving your reason.
Rana should buy shirts made from cotton. This is because cotton is a good
absorber of water. It can soak the sweat coming out of our body and expose it
to the environment. Thus, it helps in evaporating the liquid (sweat), thereby
cooling our body.

8. Explain the difference between thermoplastic and thermosetting
plastics.

Thermosetting plastics Therm oplastics



Thermosetting plastic cannot be
Thermoplastic can be bent

bent easily. It may break when

easily.

forced to bend.





Thermo setting plastic cannot
Thermoplastic can be

be softened by heating. Thus, it

softened easily by heating.

cannot be reshaped once

Thus, it can be reshaped.

moulded.

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9. ‘Manufacturing synthetic fibres is actually helping conservation
of forests’. Comment. (

Raw materials for natural fibres are mainly derived from plants and this means
cutting a lot of trees. This leads to deforestation. But raw materials of synthetic
materials are mainly petrochemicals. Hence, manufacturing synthetic fibres
helps in the conservation of forests.

10. Categorize 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.

Cannot be
Can be recycled


recycled





Telephone instrum ents Plastic toys



Cooker handles Plastic chairs



Electrical switches Carry bags



Plastic covering on electrical

wires



Ball point pens



Plastic bowls




11.Describe an activity to show that thermoplastic is a poor conductor
of electricity.
We will design a circuit to see that thermoplastics are poor conductors of
electricity. We need a bulb, some wires, a battery, a piece of metal, and a
plastic pipe. Set up the circuit first with the metal and then with the plastic
pipe (as shown in the figure). After you switch on the current, you will
observe that the bulb glows in the former case. In the latter case, the bulb
does not glow. Hence, a plastic pipe (which is a thermoplastic) is shown to
be a poor conductor of electricity.












12.‘Avoid plastics as far as possible’. Comment on this advice.
Plastics are non-biodegradable. Once introduced into the environment, they
take several years to decompose. Plastics add to the environmental pollution. If
they are burnt, release poisonous gases. Plastic bags thrown in the garbage
dump are swallowed by animals like cows and choke their respiratory system and
can even prove fatal. Therefore, we should avoid plastics as far as possible.
Question Bank

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Very Short Answer Questions (1Mark)
1. Define man-made fibers?
The fibers which are obtained from petro chemicals are called as man-made
or synthetic fibres.

2. Define Nylon?
Nylon is one of the most elastic synthetic fabrics which do not lose strength
even after repeated use.

3. Define Polyester?
Polyester is a synthetic fiber which is wrinkle resistant, strong, light
weight and elastic.

4. Define semi synthetic fibers?
The fibres which are prepared from petro chemicals and natural material are
called semi synthetic fibres.

5. Why are ropes made of nylon used in elevators and cranes?
Nylon is strong, elastic, light-weight and easy to wash. So it
is used in elevators and cranes.

6. Name of the synthetic fibre which resembles silk and wool.
Terry wool and terry silk.

7. Why electric wire has a plastic coating. Give reason.
Plastics act as a insulator, so the electric wire has plastic coating.

8. Why the handle of Cooking pans made of plastics.
Plastics allow very little or no heat through them. So the cooking pans
have handles made of plastics.

9. Clothes made of synthetic fibres are not very comfortable to wear.
Give reason.
Synthetic fibers are hydrophobic in nature. So they cannot absorb water.

10. Differentiate between Rayon and Nylon.

Rayon is semi synthetic fibre where as nylon is totally a synthetic fibre.


Short Answer Questions- Type -1 (2Mark)

1. What is polymer? What is polymerization?
Many monomer units combine to form a large single unit called polymer.
The process of combining these monomer units into large polymer is called

polymerization.

2. Do polymers occur is nature? If yes, give example?
Polymers occur in nature. Ex:Heamoglobin present in blood, is a protein
formed by joining many amino acids.

3. What are biodegradable materials? Give examples
A material which gets decomposed by a natural process, such as action
by bacteria is called as bio-degradable material. Ex: Paper, vegetable,
Fruits etc...

4. What are non- biodegradable materials give? Give examples.

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A material which is not easily get decomposed by a natural process is called
as non-biodegradable material. eg : Plastics.

Short Answer Questions- Type -2 (3Mark)

1. What are thermoplastics? Give examples and use.
The plastic which can be re-moulded on heating is known as thermoplastics
Ex: PVC (poly vinyl chloride) retains their plasticity even after repeated heating
and cooling. So they are used to make bags, toys etc.

2. What are thermosetting plastics? Give examples and use.
The plastic which can't be re-moulded on heating is known as Thermo
setting plastics E.g.: Bakelite, Melamine, Bakelite is an insulator and is
used to make electrical switches and hardens of various intensely.
Melamine has fire resisting and heat resisting properties and is used to
make floor tiles, kitchen wares etc.

3. What are spandexes? Why is spandex suitable for making clothes
which require a body hugging fit like swimming costumes?
Spandex is a long chain synthetic polymeric fiber. It is soft, rubber like and
allows the fibre to stretch a lot and then recover its original shape. The high
elasticity of the fabric make from these fibers is suitable for making clothes
which require a body hugging fit like swimming costumes, undergarments etc.

4. .Give few advantages of synthetic fibre.

1. The fibre has high tensile strength to with stand heavy loads
without breaking.
2. Have elasticity which regains the original shape after stretching.
3. Easy to maintain.
4. Production of the fibre is independent of agricultural crops.
5. It is not affected by chemicals, moisture, bacteria etc.
6. Very low cost compared to natural fibers.

5. List few disadvantages of synthetic fibres.
a. Synthetic fibres are hydrophobic. They do not allow our skin to breathe.
Not only they are incompatible but also affects health as our body uses the
skin to eliminate toxins through sweat.
b. It melts when exposed to fire.
c. Over ironing causes the material to shrink and hence loses its shape.

Long Answer Questions (5 Marks)

1. What is polyester? Give example. How terry cot, terry wool and terry silk
are prepared and what are their uses.

Polyester is a synthetic fibre,
Eg Terylene, terry cot, terry silk, terry wool
Clothes made from polyester fabrics have excellent wash
wear characteristics and therefore require minimum care.
Terylene is mixed with cotton to produce:

1. Terry cot: It is used to make dress materials such as shirts, skirts etc.
2. Terry wool: Is used to make suits etc.
3. Terry silks: Is used to make sarees, Dress materials etc.

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2. What are plastics? Give important characteristics of plastics.

Plastics are polymers that can be moulded into different shapes and size.

1. Plastics are non- reactive as they do not react with water and air and also
do not corrode easily but are sensitive and melt upon heating.
2. Can be moulded into various shapes and sizes.
3. Do not show thermal conductivity as it is a bad conductor of heat.
4. Do not show electrical conductivity so electric wires are coated with plastics.

Value Based Questions
1. Why are synthetic clothes uncomfortable to wear in summer ?
Synthetic fibers are hydrophobic. In summer, our body produces more sweat.
If we wear synthetic clothes it will not absorb sweat. Hence it is
uncomfortable to wear in summer.

2. Why should you not wear synthetic clothes while working near fire?
Synthetic fibers melt before burning. As a result the clothes made of
such fibers melt and stick to the skin in case of fire and cause heavy
burns.

Activity Based Questions

1. Observe the following figure and answer the following questions:

(a) Identify the articles used by the persons in the figure.

(b) Name the substance used in making these articles.

(c) Why does this substance is used in making these articles?

























Ans. (a) The articles are parachute and ropes for rock climbing.

(b) The substances used in making these articles is nylon.

(c) Nylon is actually stronger than steel, so it is used in making these
articles

Q. 2. Draw a diagram to show the:

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(a) Linear arrangement of units in plastic.

(b) Cross linked arrangement of units in plastic.


Ans :



(a)






















(b)


(a) Linear and (b) Cross-linked arrangements

Q. 3. Observe the following articles and name the substances used in making
these articles:


























Ans. The articles are as follows

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` (a) Chair (b) Bucket
(c) Glass (d) Toy Scooter

These articles are made up of the polymer called plastic.

Multiple Choice Questions (1 Mark)
1. Choose the correct statement.
a) Monomers combine to form polymers
b) Polymers combine to form monomers.
c) Monomers and polymers do not exist
d) Both a & b

2. Which of the following is also called artificial silk?
a) Nylon b) polyester c) Rayon d) Acrylic

3. Rayon:
a) Is obtained by chemical treatment of wood pulp
b) Can be woven like silk fibre
c) Can be dyed in a wide variety of colours
d) All of them

4. Nylon is used to make.
a) Clothes b) Socks and ropes c)Tents and parachute d) All of them

5. Nylon is a
a) Semi-synthetic fiber
b) One of the most elastic synthetic fabrics
c) Substitute for natural wool
d) All of them


6. Terry cot is a blend of….
a) Terylene and cotton b) Terylene and wool
c) Terylene and silk d) All of these

7. A polyester which is used to make utensils, wires and film roles is
a) Terylene b) Dacron
c) PET (polyethylene tetra phthalate) d) All of them

8. Substitute for natural wool is
a) Rayon b) Nylon c) Polyester d) Acrylic
9. Terry wool is a blend of….
a) Terylene and cotton b) Terylene and wool
c) Terylene and silk d) Terylene only

10. Which of the following acts as an insulator and used to make electrical
switches?
a) Bakelite b) Melamine c) Polyethene d) PVC

11. Which of the following is used to make floor tiles, kitchen ware and
fire resistant fabrics
a) Bakelite b) Melamine c)Polyethene d)PVC

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12. Plastics are
a) Strong, light-weight and durable b) Non- reactive
c) Do not show thermal conductivity d) All of these


Key:

1(a) 2(c) 3(d) 4(d) 5(b) 6(a)

7(c) 8(d) 9(b) 10(a) 11(b) 12(d)

Fill in the Blanks (1 Mark)

1. The process of combining the monomer units into large polymer
is called.................

2. ........................ present in blood, is a protein formed by joining many
amino acids.
3. ............... was first obtained by chemical treatment of wood pulp.
4. ............... was the first totally man-made synthetic fibre without using any plant
or animal source.
5. .........................is a blend of Terylene and wool.
6. ...................is made of many ester units which may be synthesized from
petroleum products.
7. . . . . . . . .. .. .. . .. .. .. .. .
is the sole constituent of cotton fibres and is made of a large
number of glucose molecules.
8. Nylon is used to make parachutes because it has high
........... ... .. .. ..

9. Synthetic fibres do no absorb water and are....................... in nature
10. Animals swallow............................. while grazing and get choked.

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11. Plastics do not show.......................................

12. Polythene is a polymer of.................

13. Synthetic fibres are also called …………. or ………….. fibres
14. Synthetic fibres are synthesized from raw materials called ……..

15. Like synthetic fibres, plastic is also a ……………

Answers:





4. Nylon ( ) d. Fabric which do not wrinkle easily

Key : 1 - d 2- c 3 - a 4-b



















1. Polymerization 2. Hemoglobin 3. Rayon 4. Nylon
5. Terry wool 6. Polyester 7.Cellulose 8. Durability
9.Hydrophobic 10.Polythene bags 11.Electrical conductivity 12.
Ethane 13.Artifical ,man-made 14. Petrochemicals 15. polymer

IV. Match the Following
Column-A Column-B
1. Polyester ( ) a. Prepared by using wood pulp
2. Teflon ( ) b. Used for making parachutes and ropes
3. Rayon ( ) c. Used to make nonstick cookware