Class 7 Science Chapter 3

1. Fibre to
Fabric
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LEARNING OBJECTIVES
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After completion of the chapter, students will be able to
1. define fibre and fabric.
2. differentiate between natural and synthetic fibres.
3. explain the rearing and breeding ofsheep
4. describe the processing ofwoo.
5. describe the life history of silk worm and what is sericulture.
6. learn about the different varieties ofsilk.
7. enlist the diseases that affect the workers in sericulture industry.
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We wear clothes to protect our body from heat, cold, dust, insects, etc. It is
the basic need of our life. Clothes are made from fibre which is a long, strong
and flexible thread like arrangement. Fibres which are obtained from plants
or animals are termed as natural fibres and the one which are man-made are
known as synthetic fibres. We wear clothes made of nylon, wool, silk, rayon
etc.
FIBRES
Natural Fibres Man-made Fibres
Wool Silk Nylon Polyester
Wool
Wool is a natural fibre obtained from the fur of the animals like sheep, goat,
yak, rabbit, alpaca, camel and llama. These wool yielding animals have a thick
coat of hair on their body to keep them warm during the cold winter season.
The wool which is commonly available in the market is sheep wool. Yak wool
is common in hilly regions of Tibet and Ladakh. Mohair is obtained from
angora goats found in hilly regions such as Jammu &Kashmir. The under fur
of Kashmiri goat is soft. It is woven into fine shawls called Pashmina shawls.
Do You Know?
Wool is grown not made. Every
year sheep grow a new fleece
Wool products use less energy
than man-made flbres during
manufacture
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DoYouKnow?
The thickness of the wool fibre
corresponds to the amount of
crimp. Fine wool lilke Merino have
up to a hundred crimps per inch.
Wool is a modified hair fibre, first made from inner coat of wild sheep from
Central Asia. The wool fibre has been in use since the times people used ston
knives for removing the hair coat of sheep. In the beginning, the outer coat of
sheep that was coarser was also spun, but selective breeding has produced
sheep with inner (finer) fibres.
Alpaca
Llama
Yak
Sheep
Animals that give wool
ACTVTY3.1
Procure outline maps ofIndia and the world.
Find out and mark the places on the map where you find animals that provide
wool.
Use different colours to denote the location for different wool yielding
animals.
Properties of Wool
The following properties of wool make it a useful natural fibre
Sunsafe: Wool has naturally high UV protection.
Flame retardant: Wool fibre has a higher ignition threshold than many
other fibres and is flame retardant up to 600°C. It also produces less toxic
fumes in fire.
Do You Know?
Shahtoosh is the king of wools. It
is the undercoat of the Tibetan
antelope. It is considered to be
world's finest and warmest wool.
Biodegradable: When disposed off, natural wool fibre takes only a few
years to decompose.
Breathable: Wool's natural structure allows it to absorb and release water
vapour into the atmosphere, keeping you warm in winter and cool in
summer
Non-allergenic: Wol is not known to cause allergyand does not promote
the growth of bacteria. With microscopic scales, wool fibres can trap dust
in the top layers until vacuumed away.
Durable and elastic: Wool fibre can be bent 20,000 times without breaking
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3. Fibre to Fabric
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and still have the power to recover and return to its natural shape.
Easy care: Modern wool can be machine-washed; retaining a small amount
of natural oil, wool fibre resists dirt and grease.
Easy to spun: Since wool fibres are scaly and naturally interlocked, they can
be easily spun.
Uses of Wool
Wool is used to make sweaters, shawls that keep us warm in winters.
It is used to make blankets, upholstery, carpets, etc.
It is used insoundproofing
Rearingand Breeding of Sheep
Sheep rearing indicates looking after sheep by providing food, shelter and
health care. Sheep feed on plants, seeds and grains so they are known as
herbivores and the people who take care of them are known as shepherds.
Rearing of sheep in mountains and deserts is very frequent. This is because
abundant fodder is available in the large deserts and forests. Therefore,flock
of sheep may be moved from place to place to take advantage of cheap feeds
and natural fodder forage. You can meet grazing flock of sheep underthe
control of shepherds in great desert of Rajasthan and in the forests
of Madhya Pradesh, Maharashtra and Karnataka. Sheeps have a
lifespan of about 10-12 years. They eat grass and leaves. In winter,
sheeps are kept indoors and fed on leaves, grain and dry fodder.
Many types of sheep are bred for their fine wool and can easily adapt
themselves to semi-arid conditions with the ability to produce large
Uses of wool
amounts of wool fibres.
Breeding is mainly done to acquire animals with desired quality. The
two sheep of desired quality are selected as parent and they are
crossed to attain new breed of sheep having the best chosen quality of both
parents (such as soft under-hair). This type of breeding is known as selective
breeding. This way the high-yield breeds of sheep are produced. These types Do You Know?
of sheep have thick coat of hair and good quality wool.
Rearing of sheep
Processing Fibre Into Wool
There is a long process which is followed to obtain wool from the fleece of
sheep. A sheep or yak body has a thick coat of hair known as fleece. Let's
study about these steps in detail.
More than 40 breeds of sheep
ive in India, though not all of
them are readily available. Sheep
are critical to India's economy,
used to produce carpet, dothing
and mutton. A 2003 census
revealed that the country
has a sheep population of
615 million
Shearing
The first step involves shearing. The process of removing the
fleece using special clippers is called shearing. Shearing is done
manually with a razor or with the help of a shearing machine.
Generally, hair are removed during the hot weather which enables
sheep to survive without the protective coat of hair. Shearing does
not hurt the sheep because the uppermost layer of the skin which
is removed along with fleece is, dead. Also, the hair of sheep grow
again just as our hair does.
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Scouring
Scouring is the process of washing the sheared fleece
ingis done
of
wit
which has dust, dirt, oil, grease, etc. These days scouring isdon
the help of machines.
Sorting
ferent texture
Sorting is the process of segregating or separating differenttext
of fleece.
The wool is sorted into different categories which depend upon its qualit
The fleece having long fibre is sent to the factory for aditinn
processing. Small fluffy fibres named as burrs are picked outto
the hair (similar to the ones that often appear on our sweaters). The
fibres are again scoured, dried and are ready to be drawn intofibres
8ebutng by maohines
Dyeing
The natural fleece of sheep
have white, black or brown
colour. But it can be dyed in different
colours by the process known as
Sorting
dyeing.
Dyeing
Combing
Here, the fibres are straightened, combed and rolled into yarn.
Hair are sent into a 'carding' machine. It combs the loose wool
fibres into a sheet. This sheet is twisted into a rope or sliver. This
sliver is twisted and stretched into a yarn.
The yarn is wound to form balls of wool. These balls are used
to make sweater and other warm clothes. The finest quality of
wool is derived from the fleece of Merino sheep'. The quality of
wool is determined by the fibre diameter, crimp, yield, colour and
strength.
Combing
Spinning
The wool fibres are straightened and then spun or twisted together into yarn.
The yarn is either knitted or woven into pullovers and different woollen attires.
The good quality wool is judged on the basis of its thickness, length, strength,
shine of the fibre. The longer fibres are used to make knitted sweaters and the
shorter ones are used for making woollen carpets or cloth.
PROCESSING OF WOOL
Spinning Shearing Scouring Sorting Dyeing Combing Spinning
Removing
hair from
Washing
fleece to
Adding
colour
Separating9
long, fine
quality fleece
from broken
Removing
burrs from
Spun or
twisted to
the body
of animal
remove dirt,
dust, sweat,
to wool fleece make yarn
grease pieces
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5. Fibre to Fabric
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Types of Wool
The market value of wool primarily depends on fineness and length of its
fibres. The following systems are followed in wool processing
Woollen system: Woollen fibres are of mixed lengths are carded and spun to
form woollen yarn.
Worsted system: Woollen fibres are combed, thus separating the long and
short fibres. The long fibres are then formed into smooth compact strands,
which are spun to form woollen yarn.
Occupational Hazards in Wool Industry
Many people earn their livelihood by working in the wool industry. People who
work as sorters get infected by a bacterium, anthrax, which causes a fatal
blood disease called Sorter's disease. This is very common in wool industry.
Noise, inadequate lighting, high temperatures and humidity levels required for
wool processing may have an adverse effect on the health of workers.
ACTVIY32
Debate amongst your classmates whether it is fair on the part of humans to rear
sheep and then chop off their hair for getting wool.
Sampleuestions
Q.1. Give reasons forthe following:
(a) Light coloured cotton clothes are preferred to be worn in summers.
(b) Shearing does not hurt a sheep.
(c)We wear different types of clothes in different weathers.
Ans. (a) Light colours are poor absorbers of heat. So, in summers they keep us
cool.
(b) During shearing the uppermost layer of sheeps skin which is dead is
removed. Therefore, it does not hurt the sheep.
(c)We wear clothes according to the climate. In summers we wear clothes
that keep us cool and in winters we wear clothes which keep us warm.
Q.2. What unusual qualities ofwool make it a very useful fibre?
Ans. (a) It captures air between its layers.
b) Because of its crimp it is bulkier and acts as insulator.
(c) It readily absorbs moisture.
MCHECK YOUR PROGRESS
1. Write the correct sequence in the processing of wool.
2. Why is rearing of sheep in mountains and deserts very frequent?
SILK
Silk is a natural protein fibre. It is strong, soft, shiny and a very fine fibre procured
from silkworm. It is one of the strongest natural fibres and it is said that a silk
yarn is as strong as a thread of steel. The silk fibre is made into yarn which
IS used in making saris, scarves etc. The rearing of silkworms for obtaining Silk fabric
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6. produce
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origin
a plenty of silk on a commercial scale. Ihe silkworm moth was
native of China. Later it was introduced to Europe, the Mediterranll
silk is known as sericulture. It IS a very Old Occupationi li iiula. Ihdia.
interestin
other Asiatic countries. Let's study about the life-history of this int
creature in detail.
Do You Know? Life History of Silk Moth
Pupa- Adult Silkworm
India is the world's second
Larva
Egg
largest producer of slk following
China ) The female silk moth lays eggs on
mulberry leaves from which
larvae called caterpillars
or silkworms hatch out.
The silkworm feeds on
Mating of male and
female silk moth
mulberry leaves and Cocoon with
developing
grows in size.
moth
(i) It then enters the next
stage of its life cycle
called Pupa. It first
Eggs on
mulberry
leaves
weaves a net to hold Cocoon
itself. Then it swings its
head from side to side in
the form of figure 'eight'.
During these movements, it
secretes a fibre made of protein,
which hardens on exposure to air.
This is a silk fibre. It covers itself completely by silk fibre to form a cocoon
At this stage, the larva is called a pupa. The further development of the
pupa takes place inside the cocoon. Cocoons are shades of white, cream
and yellow.
Silkworm
Life cycle of silk moth
ii) On reaching adulthood, the moth breaks out of the cocoon. Again the male
moth mates with the female which lays eggs and the cycle is repeated all
Over again.
From Coc0on to Silk
Rearing Silkworms
Under this process, the silkworms are taken good care of by giving them
adequate food and shelter. The female silkworms are kept separately in
disinfected linen bags. Here, the female lays eggs. Each female silk moth lays
200 to 500 eggs at one time. The eggs are shifted into a perforated carton
or on bamboo trays under best suited temperature and humidity. They are
incubated inside the incubator for larva to hatch from eggs. The mulbery
leaves are kept over the incubator in a perforated sheet of paper for the larva
to feed, which hatch out of eggs. The larva eats day and night and yrows in
size. After 30 days the silkworm does not eat and clings onto the small rack
or twigs to spin cocoon. The silkworm completes its cocoon within 4-5 days.
The cocoon is about 4-5 cm long which contains 600-1200 meters ofthin silk
fibre.
Silk moth eggs
bamboo tray
Processing Silk
Silkworms on mulberry
Production of silk involves gathering of cocoons and killing of moths inside
leaves in rack
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7. Fbre to Fabric
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them. When all the cOcoons have been gathered, these are first boiled,
exDOsed to steam or treated in ovens. The silk fibres separate out,
when the boiling water dissolves the gummy substance that holds the
OCOon filament. This filament from four to eight cocoons are joined,
COC
wisted and are then combined with other filaments to make a thread
twis
that is wound on a reel. This process of taking out thread is known as
reeling or filature. The resulting, raw silk thread is sufficiently strong
for weaving or knitting. Ihe thread is continuous and made up of
extremely long fibres.
Along with cocoons damaged by emerging worms (used for breeding), 1
the filaments from large outer portion of the cocoon are removed (by
brushing) before reeling, and the inner portion of the cocoon (that
remains after reeling) are mixed to produce a low grade silk staple that
is spun into yarn through a procedure called throwing. This silk then
is reeled into skeins and packed into small bundles called books and
then shipped to silk mills around the world. Four different types of silk
threads may thus be produced viz., organzine, crepe, tram and thrown
singles.
Steaming cocoons
Reeling
Properties of Silk
It has a smooth and soft texture.
DoYouKnow?
t takes about 110 silkworm
cocoons to make one good
silk t
It is the strongest natural fibre.
It is cool to wear in summers and warm to wear in winters.
It absorbs moisture.
ACTVTY33
Take a piece of natural slk fabric and another piece of artificial silkfabric.
Burn them separately.
Observethe difference in the smell produced during burning.
You will observe that the natural silk wil give a smell of burninghairwhereas
artificial silk will give a smell of burning paper.
Just like silk, wool is also made of proteins. So, it also burnsgiving the smell
of burning hair.
Uses of Silk
It is used to make clothes, scarves, sarees and dresses.
It is used in bullet-proof vests and in parachutes.
It is used as non-absorbable sutures in surgery.
Occupational Hazards in Silk Industry
Working in cramped, poorly ventilated rooms during production of silk
leads to breathing problems.
Handling of dead worms with bare hands results in infection and illness
among workers.
Workers have to focus on fine thread being reeled and have to stand
for 12-16 hours a day which result in backache, vision problems and leg
deformities like bow leggedness. Uses of silk
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