Science Chapter 3 : Synthetic Fibres And Plastics
Q1) What is Natural fibres ?
Ans : They are fibres which are obtained from natural sources like plants and animals. Eg: silk,
wool, cotton ,etc.
Q2) What is synthetic fibres ?
Ans : They are obtained from natural material but by chemical processes. It is a chain of small
units combine together to form a large unit known as polymers. Eg: rayon, polyester, nylon,
etc.
Q3 ) Petro chemicals Ans : All the synthetic fibres are prepared by a number of processes using raw material of
petroleum origin known as petrochemicals.
Q4) Polymer Ans : The molecules which are made by a combination of repeating units called monomer. It is
a two greek word 'poly' meaning many and 'mer' meaning part. So polymer is made of many
repeating units.
Q5 ) Biodegradable Ans : Substance that are decomposed by bacteria activity and various other natural processes
over a period of time. Eg: fruits and vegetable peels, paper ,etc.
Q6 ) Non Biodegradable Ans : Substances which cannot get decomposed by bacterial activity and other various natural
processes. Eg: plastics, glass, etc.
Q7) Characteristics of Synthetic fibres or Advantages
Ans :
1.
2.
3.
4.
5.
6.
7.
8.
9.
Light in weight
They are durable
They have high tensile strength
They are cheaper as compared to natural fibres
Does not attract insects and moths.
They are easy to maintain and wash
They dry up quickly.
They are less expensive.
They are readily available
Q8 ) Disadvantages of synthetic fibres
Ans :
1. Non eco friendly material
2. They are non-biodegradable, they can't be decomposed
3. Made up of chemicals so when we burn them they release toxic and harmful gasses that
harm the environment
4. These fibres are irritant to skin as they make us uncomfortable and also they don't allow
air to pass and cause allergies when we wear them.
5. These fibres don't absorb heat and water.
6. Catch fire easily
Q9 ) Types of Synthetic Fibres
Ans : 1) Rayon : It is obtained by chemical treatment of wood pulp. It is also known as artificial
silk.
Properties1. It has silky texture.
2. It is cheaper than pure silk and can be woven like silk fibres.
3. It can be dyed in variety of colors.
Uses1. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets
2. It is also used as bandages for surgical treatments and dressing.
2) Nylon : It is man made fibre. It is prepared from coal, water and air. It was the first fully
synthetic fibre
Properties1.
2.
3.
4.
5.
6.
Its stronger than steel wire, elastic and flexible.
It has a high tensile strength.
It is durable.
It has low absorption capacity.
It is highly inflammable.
Nylon is strong, elastic and light. It is lustrous and easy to wash. So it is very popular for
making clothes
Uses1. Used in making parachutes bristle of toothbrush, ropes, curtains, socks, sleeping bag,
curtain and tents.
2. It is used for making parachutes and ropes for rock climbing.
3. Terylene is a popular polyester. another Eg polyethylene terephthalate
3) Polyester :
Polyester is actually made up of the repeating units of a chemical called an ester. Esters are
the chemicals which give fruits their smell. Eg Terylene
Properties1. It does not wrinkle easily.
2. It remains crisp and easy to wash.
3. It is light and durable. It takes very less time to dry.
Uses1. It is suitable for making dresses and other clothes
2. It is mixed with various fibres to make blended fabrics like for eg : polycot, polywool,
terrycot etc
4) Acrylic :
Properties1. It is produced by organic compounds. It has a wool like texture and that is why it's
known as artificial wool.
2. They are available in variety of colours.
3. It is cheaper than natural wool.
Uses1. It is used in making sweaters and shawls.
2. It is used to make water proof acrylic paints.
5) Plastics : Plastic is also polymer like synthetic fibre. All plastics do not have same type of
arrangement of units..On the basis of their linkage they are divided into 2 types-Thermo
plastics n Thermosetting
Q10) Give examples which indicate that nylon fibres are very strong.
Ans : Nylon fibres are strong so they are used for making parachutes and ropes for rock
climbing.
Q11) Difference between thermo plastics and thermosetting plastics
Ans :
Thermo plastics
They can be easily moulded and change their
shape again and again.
They are linear linked.
Thermosetting
They cannot be moulded and change their
shape.
They are cross linked.
They are flexible.
They are not flexible.
Eg : PVC and polythene.
Eg : Melamine and Bakelite.
Q12) What are the advantages of plastics ?
Ans : Advantages of plastics containersa)
b)
c)
d)
e)
Plastics is light, strong, durable and can be moulded into different shapes and sizes.
Plastics do not react with food items. Hence used to store food
Plastics are economical and cheaper than metals.
It does not react with air or water. They are not corroded easily.
Plastics are poor conductors of heat and electricity.
Q13) Write disadvantages of plastics or Avoid plastics as far as possible, Comment.
Ans : There are many disadvantages of using plastics . Namely :
1.
2.
3.
4.
5.
6.
Plastics are non-biodegradable materials. So use of plastics is harmful for environment.
The plastics cannot be finally disposed off.
Plastics takes several years to decompose, so they are not eco-friendly.
Plastic causes environmental pollution.
Burning of plastics gives out toxic fuels. These can be hazardous to health.
Plastic bags thrown in the garbage dump are swallowed by animals like cows. These
plastic bags choke their respiratory system and can even prove fatal. Therefore, we
should avoid plastics as far as possible.
Q14) Give example to show that plastics are non corrosive in nature.
Ans :
1. They do not react with any substances.
2. Plastics do not react with air and water which are essential for corrosion.
3. They do not show any chemical reaction.
Q15) Should the handle and bristle of a tooth brush be made of the same material ?
Ans : No handle and bristle of tooth brush should not be made of same material. The
handle should be hard so that it gives the firm grip. While bristle should be made of the
soft materials so that it does not harm the gum of the teeth.
Q16) Manufacturing synthetic fibres is actually helping conservation of forest. Comment
Ans : The natural fibres required the raw materials from plants and animals. So lead cutting
of trees and killing of animals. Synthetic fibres are man made fibres which are made up of
chemicals and these chemicals are not available in forest. So manufacturing synthetic fibres
is actually help in conservation of forests.
Q17) Why should we not wear synthetic clothes while working in the kitchen ?
Ans : Synthetic fibres melt very soon on heating. If the clothes catch fire, it can be
disastrous. The fabrics melt and stick to the body of a person wearing it.
Q18) Why plastics are used in the industries and house hold articles ?
Ans : Plastic is very light, strong, durable and can be moulded into different shapes and
sizes. It is used in various purposes. Plastics are generally cheaper than metals. They are
widely used in industries and household articles.
Q19) Melamine crockery is very popular. Why? Or One use of melamine
Ans : Melamine is a type of thermosetting plastics. It can resist fire and can tolerate heat
better than any other plastic. It has a shining surface, economical and make an unbreakable
kitchen ware.
Q20) Buckets are made of plastics these days. Why?
Ans : This is because they are of light weight, have good strength and are durable. They are
also very cheap and are non-reactive to water.
Q21) Bakelite plastic is used to make electrical switches. Why?
Ans : Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It
is a hard, stiff, durable having a very high melting point.
Q22) Chemicals are stored in plastic bottles. Why?
Ans : Plastics unlike iron do not react when left exposed to water, moisture and air.
Hence, they are used to store chemicals.
Q23) Plastics used are in cars, aircrafts and spacecrafts. Why?
Ans : Plastics are used to make cars, aircrafts and spacecrafts as they are light in weight
than metals. It helps the vehicle to float in air or be moved easily on land. It is also durable
has good strength and easy in handling.
Q24) Melamine coating is done on units of firemen. Why?
Ans : Firemen have to go close to fire places so that they can spray water to stop it but
during this they also might catch fire on their costumes. Hence, melamine is coated on their
suitsas they are fire resistant and heat tolerant
Q25 ) Write use of plastic in health care industries ?
Ans : Some used of plastic in health care industries are 1. Blood is stored safely in plastic bags
2. Many medicines are packed in plastic
3. Gloves of surgeons are made up of plastic.
Q26 ) Name the first fully synthetic fibre ?
Ans : Nylon
Q27 ) What is the name of cotton polymer ?
Ans Cellulose
Q28 ) Polycot is made by mixing which two fibres ?
Ans : Polycot is a mixture of polyester and cotton
Q29 ) Explain why some fibres are called synthetic.
Ans : While natural fibres are obtained from plants and animals, synthetic fibres on the
other hand, are obtained by human beings from the chemical processing of
petrochemicals. These are made of small units that join together to form long chains. Some
of the examples of synthetic fibres are nylon, rayon, acrylic, polyester etc
Q30 ) Electric switches, plugs and sockets are made of thermosetting plastics.
Ans : Bakelite is used for making electrical switches, plugs and sockets. It is is a poor
conductor of heat and electricity. It resists fire and can tolerate heat better than other
plastics. Hence it prevent possible fire in electrical installations due to overheating n also
saves us from receiving electric shock while using them.
Q31 ) What is the arrangement of monomers in thermoplastics and thermosetting
plastics ? what changes does it bring about in the properties ?
Ans : Thermoplastic have linear polymer chain. Such plastics gets deformed easily on
heating and can be bent. whereas Thermosetting plastics use cross linked polymer. These
substances that do not soften under heat and pressure and cannot be remolded or
recycled.
Q32 ) Why the following are made of thermosetting plastics? Explain. i) Saucepan handles
Ans : Thermosetting plastics are used to make saucepan handles because on heating, these
plastics do not get softened and also it is a bad conductor of heat and electricity.
Q33 ) By giving a reason, suggest Mahesh as to why he should buy a cotton shirt for
summer and not a synthetic shirt.
Ans : Mahesh should buy a cotton shirt for the summer and not a synthetic shirt because
cotton is a good absorber of water. So it can soak the sweat coming out of the body and
expose it to the environment. Thus, it helps in evaporating the sweat and helps in cooling
our body.
Q34 ) Name the fibre which is obtained by chemical treatment of wood pulp?
Ans : Rayon
Q35) What is PVC ?
Ans The full form of PVC is Poly vinyl chloride.It is a type of thermoplastic. It is used in food
packaging, making of sanitary pipes.
Q36 ) Polycot is made by mixing which two fabrics ?
Ans: Polycot is a mixture of polyester and cotton.
Q37 ) Name a polymer occurs naturally?
Ans : Polymers that occur naturally is cellulose. Cellulose is made up of a large number of
glucose units.
Q38) Although rayon is obtained from a natural source, wood pulp, yet it is a man-made
fibre. Why?
Answer : This is because rayon is obtained by chemical treatment of wood pulp.
Q39 ) Why does Nylon become very popular for making clothes for mankind?
Answer: Nylon is the first fully synthetic fibre prepared from coal, water and air in 1931.
Nylon fibres are strong, elastic and light. It is lustrous and easy to wash. So, it became very
popular for making clothes.
Q40) Why does polyester fibre quite suitable for making dress material?
Answer: Fabric made from Polyester fibre does not get wrinkled easily. It remains crisp and
is easy to wash. So, it is quite suitable for making dress material. Terylene is popular
polyester.
Q41 ) Name a form of polyster which is used for making bottles, utensils, films, wires and
many other useful products?
Ans: PET: PET (polyethylene terephthalate) is a form of polyster.
Q42 ) Uses of PET
Ans : It is used for making bottles, utensils, films, wires and many other useful products.
Q43 ) Pertro chemicals :
Ans : All synthetic fibres are prepared by a number of processes using raw materials of
petroleum origin called petrochemicals.
Q44 ) Fibre :
Ans : The thread like structures which are woven together to give us fabric.
Q45 ) Write any two uses of plastics in healthcare industry.
Ans




Packaging of tablets
For making threads used for stitching wounds
For making syringes
Making gloves used by doctors
Q47 ) Can plastics be used for making cookware in microwave oven ?
Ans :
Q46 ) What is the difference between nylon and rayon?
Ans :
Rayon
Nylon
Rayon is neither a fully synthetic nor a fully
natural fibre.It is a semi-synthetic fibre
It was the first truly synthetic fibre.
Rayon is made from wood pulp.
Nylon is made from coal, water and air.
Rayon is used for making curtains, bedsheets,
etc.
Nylon is used for making socks, rope,
toothbrush, parachute, etc.
Q47 ) Difference between linear and cross linkage.
Linear
Cross Linkage
Linear Polymers a polymer consisting of a
single continuous chain of repeat units
Thermoplastic have linear polymer chain
They r more flexible
Eg polythene
Crosslinking is the process of chemically
joining two or more molecules by a
covalent bond.
Thermosetting plastics use cross linked
polymer
They are more rigid.
Eg bakelite
Q48 ) Types of Plastics :
Ans :
Name
Bakelite
(thermosetting)
Properties
Melamine
(thermosetting)
Bad conductor of electricity
Non-reactive
Hard and stiff
High melting point
Bad conductor
Fire resistant
Teflon
(thermosetting)
Water and oil resistant.
Fire resistant
Uses
Switches, electrical
appliances, pen, etc.
Used in making cooking
ware, pots, fans, suits of
fireman
Coating on non-stick
cookware, protective
coating on paints
Polythene
(thermoplastic)
Can be moulded into
different shapes
Flexible
Polythene bags, toys,
water pipes, etc.
PVC
(thermoplastics)
Can be moulded into
various shapes.
It is flexible.
Toys, PVC pipes,
decorative items, etc.
Q49) FILL IN THE BLANKS :
Ans :
1. Synthetic fibres are also called man made or artificial fibres.
2. Synthetic fibres are synthesized from raw material called petrochemicals.
3. Like synthetic fibres, plastic is also a polymer.
4. Fibres we get from plant and animals are called natural fibres.
5. Artificial fibres are commonly called man made fibres .
6. The simple molecule in a polymer is called monomer .
7. The material which can easily be moulded is called thermoplastic .
8. The polymer of natural fibre cotton is called cellulose .
9. The process by which artificial fibres are made from simple fibre is called
polymerisation .
10.The raw material used for the production of rayon is wood pulp.
11. Polymnite is made by the polymerisation of amide molecules.
12. Terylene is obtained by the polymerisation of molecules of Ethylene glycol and
Terephthalic acid
13.Acrylic fibre is obtained by the polymerisation of molecules of carbon, hydrogen
and oxygen .
14. PVC stands for PolyVinyl Chloride .
15.PET stands for Polyethylene Terephthalate.
16. PVC is prepared by the polymeriation of vinyl chloride molecules .
17. Two example of thermoplastic plastic and PVC .
18.The materials which get decomposed easily throgh natural process are known
as Biodegradable.
19.The natural fibres are made from simple molecule that is known as ... Monomer
20. The process by which artificial fibres are made from simple molecules is called
Polymerization
21. Terylene is a popular form of Polyester
22.Material used to make coating on non stick cookware is Teflon
23.The fibres which resemble wool are known as ... Acrylon
24.Which fibre is also known as regenerated fibre Rayon
25.The plastics in which monomers are arranged in a straight chain are known as
Thermoplastics