CLASS - VII SCIENCE

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FIBRE to FABRIC

FIBRE TO FABRIC

1. Introduction

A very thin, thread-like strand from which cloth is made is called fibre. Fabric is produced by weaving or knitting long, twisted threads called yarn made from fibres. 1.1 Variety In Fabrics The various types of fabrics which are commonly used by us are: 1. Cotton Fabrics, 2. Woollen fabrics, 3. Silk Fabrics, and 4. Synthetic fabrics

Yarn is a spun thread which is used for weaving (or knitting)fabrics. 1.2 What are Fabrics Made of? Fabrics are made of ‘yarns’ which are, in turn, made from ‘fibres’. Fibres are very thin, thread-like strands from which fabrics (or cloth) is made.

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2. Types of Fibres Fibres are of two types: 2.1Natural fibres The fibres which are obtained from natural sources like plants and animals are called natural fibres. The examples of natural fibres are: Cotton, Wool, Silk, Flax, and Jute. (a) Cotton, Flax and Jute are the natural fibres obtained from plants. (b) Wool and Silk are the natural fibres obtained from animals. 2.2 Synthetic fibres The fibres which are prepared from chemical substances in industry, are called synthetic fibres. Some of the examples of synthetic fibres are: Nylon, Polyester (like Terylene), and Polyacrylic (like Orlon). We can distinguish between the cotton, wool, silk and synthetic fabrics by performing the ‘burning test’ as follows : (i) If the piece of the fabric burns vigorously giving a smell of burning paper, then it is cotton fabric (Cotton does not melt or form beads on burning) (ii) If the piece of the fabric burns giving a smell of burning hair, then it is woolen fabric (Wool does not melt or form beads on burning). (iii) If the piece of fabric burns giving the smell of charred meat, then it is silk fabric( Silk also does not melt or form beads on burning). (iv) If the piece of fabric burns slowly giving the smell of burning plastic, then it is a synthetic fabric (Synthetic fabrics melt and form small beads on burning).

3. Some Plant Fibres (i) Cotton Cotton fibre is also known as cotton wool. Cotton fibre comes from the cotton plants which are grown in the fields by the farmers. Cotton crop is usually grown at places having black soil and warm climate. In India, cotton is mainly grown in

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the states of Maharashtra, and parts of Andhra Pradesh, Madhya Pradesh and Gujarat. The process of separating cotton fibres from the seeds is called ginning (of cotton). Ginning was traditionally done by hands by using a comb-like device. These days ginning is also done by using machines. Cotton is also used for filling pillows, mattresses and quilts. The wicks of oil lamps are also made of cotton. (ii) Flax Flax is also a plant that gives natural fibres. The fibres obtained from flax plant are called ‘flax fibres.’ The fibres are obtained from the stem of flax plant. The cloth made of stem fibres of flax is called linen. Linen is used for making bed-sheets, etc. (iii) Jute Jute fibre is obtained from the stem of a jute plant. In India, jute is mainly grown in West Bengal, Bihar and Assam. Jute crop is cultivated in the rainy season. Jute fibre is used to make ropes and jute bags. The outer covering of coconut has also some fibres on it. These are called coconut fibres. The coconut fibres are used for making ropes and mats. The fibres obtained from wood are used to make paper. Thus, paper is also made from plants. 3.1 Making of yarn from fibres Yarn is a kind of long, twisted thread. Yarn is made from fibres by the process of spinning. In the process of spinning, fibres from a mass of cotton(wool or silk, etc). are drawn out and twisted. Spinning converts fibres into yarn. Yarn can be made from fibres by using three devices: (i) Hand spindle (Takli), (ii) Spinning wheel (Charkha), and (iii) Spinning machines

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3.2 Making fabrics from Yarn Fabrics are made from ‘yarn’(long threads) by two main processes:

(i)Weaving, and (ii) Knitting

Weaving The process of making a fabric (or cloth) by arranging yarns(long threads) passing in one direction with other yarns at right angles to them, is called weaving. The weaving of yarn to make fabrics is done by using ‘looms’(A device for making fabrics by weaving yarn or threads is called a loom). There are two types of looms: handlooms and power looms.

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Knitting The process of making a fabric by interlocking loops of single yarn with knitting needles or machines is called knitting. Knitting is done by hand (by using knitting needles), and also on machines.

3.3 History of Clothing Material These days we wear clothes made of various types of fabrics to cover our bodies. No fabrics (or clothing materials) were available in ancient times. So, in ancient times, people used the bark of trees, big leaves of trees, animals skins and furs, to cover themselves.

4. Animal Fibre The two important animal fibres are:

(i) Wool, and (ii) Silk.

Wool comes from animals such as sheep, goat and yak, etc., whereas silk comes from silkworms.

4.1 WOOL

Wool is the soft, wavy (or curly) hair which covers the body of a sheep. Actually, wool is a modified form of hair that grows with a waviness.

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Animals that Yield Wool

The wool-yielding animals have a thick coat of hair on their body to keep them warm during cold winter season. The hair (or wool) trap a lot of air. Air is a poor conductor of heat. So, the air trapped in hair (or wool) of these animals prevents their body heat from being lost to cold surroundings and keeps them warm in winter. This is why the hair (or wool) of these animals is removed only once in a year at the beginning of summer season. Wool is most commonly obtained from sheep.

4.2 Some Indian Breeds of Sheep

Name of breed of sheep

Quality of wool Name of the state where found

1. Lohi Good quality wool Rajasthan, Punjab 2. Rampur bushair Brown fleece Uttar Pradesh, Himachal

Pradesh 3. Nali Carpet wool Rajasthan, Haryana,

Punjab 4. Bakharwal For woolen shawls Jammu and Kashmir 5. Marwari Coarse wool Gujarat 6. Patanwadi For hosiery Gujarat

The process of selecting parent sheep for obtaining special characteristics in their offspring (such as soft under-hair) is called ‘selective breeding’.

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Wool is also obtained from ‘goat hair’. The under-fur of Kashmiri goat is soft. It is woven into fine shawls called ‘Pashmina shawls’. Angora wool is obtained from Angora goats which are found in the hilly regions such as Jammu and Kashmir. Yaks have thick and long hair on their body which yield wool. Yak wool is common in the hilly regions of Tibet and Ladakh. The animals called llama and alpaca (which are found in South America) have hair on their body which are processed to yield wool.

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5. PRODUCTION OF WOOL

5.1 Rearing and Breeding of Sheep

Rearing of sheep means to look after the sheep by providing them feed (food), shelter and health care. The persons who look after the sheep(or rearers) are called shepherds. Certain breeds of sheep have a thick coat of hair on their body which yields good quality wool in large quantities. These are called sheep of good breeds.

Once the reared sheep have developed a thick coat of hair, the hair is cut off for getting wool. The cut off ‘wool coat’ of a sheep (alongwith a thin layer of skin) is called fleece. The fleece consists of soft woolen fibres. The fleece of sheep is usually kept in ‘one piece’.

5.2 How Wool is Obtained From Sheep

(a) Shearing. The hair of sheep along with a thin layer of skin (called fleece) are removed from the body of sheep. The process of removing hair (or cutting off hair) from the body of a sheep in the form of fleece is called shearing. Shearing does not hurt the sheep because the uppermost layer of the skin of sheep is ‘dead’.

(b) Scouring. The fleece of sheep (or cut hair of sheep) contains dust, dirt, dried sweat and grease, etc. The process of washing the fleece (cut hair of sheep) that removes dust, dirt, dried sweat and grease is called scouring.

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(c) Sorting. The process of separating the fleece of a sheep into sections according to the quality of woolen fibres (such as fine, coarse, long, short, etc.) is called sorting. The same quality wool obtained from the fleece of large number of sheep are then mixed together.

(d) Dyeing. The white woolen fibres obtained by sorting can be dyed in different colours.

(e) Combing. Combing straightens the entangled woollen fibres and also removes the small fluffy fibres (called ‘burrs’) which may be caught in them.

(f) Spinning. The long woolen fibres are spun (or twisted) into thick yarn called ‘wool’.

5.3 Occupational Hazard

The people who do the job of sorting (separating) the fleece of sheep into fibres of different qualities are called ‘sorters’. The sorter’s job is very risky because sometimes they get infected by the bacteria called ‘anthrax’ which cause a deadly blood disease called ‘sorter’s disease’. The risks faced by people working in any industry due to the ‘nature of their work’ are called occupational hazards. Sorter’s disease is an occupational hazard.

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6. SILK

Silk is a fine, strong, soft and shining fibre produced by silkworms in making their cocoons. Silk is a natural fibre which is obtained from an insect (called silk moth). The rearing of silkworms for obtaining silk is called sericulture. ‘Sericulture’ means ‘silk farming’.

6.1 Life History of Silk Moth

Silk moth is a kind of insect (which resembles a butterfly). Life history of silkmoth is interesting because silk moth is not formed as such from the eggs directly. The silk moth passes through a worm-like stage called ‘larva’ or ‘caterpillar’ (which is also called silkworm) and an encased form called ‘pupa’ during its development between the hatching of egg and formation of adult silk moth.

( Egg→Larva (or Caterpillar) →Pupa→Silk moth) (Silkworm)

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The larva (or caterpillar) of a silk moth which produces silk is called silkworm.

(i) The female silk moth lays eggs on the leaves of a tree (such as mulberry tree).

(ii) The eggs hatch to form worm-like larvae. The larvae of silk moth are called ‘caterpillars’ or ‘silkworms’. The silkworms feed on the leaves of mulberry tree and grow bigger in size. Silk is formed in liquid form in the two glands in the silk worm’s head.

(iii) When the silkworm is ready to enter the next stage of its development called pupa, it first weaves a net to hold itself. The silky covering spun by the silkworm of silk moth is called cocoon. The cocoon is made by silkworm to protect its development as ‘pupa’. The silkworm continues to develop in the form of pupa inside the cocoon to form the silk moth.

(iv) When the pupa develops fully to form an adult silk moth, then the cocoon splits up and a beautiful silk moth comes out. The adult female silk moth then lays more eggs. In this way, the life history of silk moth is completed.

In order to produce silk, the silkworm developing inside the cocoon is not allowed to mature into an adult silk moth. So, as soon as the cocoon is formed it is used to obtain silk fibres and the developing silkworm gets killed. This is because if the silkworm is allowed to mature into a silk moth, then the fully formed silk moth secretes a liquid to dissolve a part of silk of the cocoon to break it so as to come out of it and fly away. This breaking of cocoon cause damage to its silk threads and hence lowers the quality of silk.

6.2 PRODUCTION OF SILK

(i) Rearing of Silkworms to Obtain Cocoons A female silk moth lays hundreds of eggs at a time. The eggs of silk moths are stored carefully on paper strips (or cloth strips) and sold to silkworm farmers. The farmers keep these eggs at suitable temperature and humidity under hygienic conditions. The eggs are then warmed to a suitable

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temperature for hatching. When the eggs hatch, silkworms come out of eggs.

(ii) Processing of Cocoons to Obtain Silk Fibres

All the cocoons are collected at one place. The pile of cocoons is used for obtaining silk fibres. The process of taking out silk fibres from the cocoons for use as silk is called reeling. Reeling is done in special machines which unwind the fibres of silk from cocoons. (iii) Converting Silk Fibres into Silk Cloth Silk fibres obtained from cocoons are spun (twisted) to form silk threads called ‘silk yarn’. The silk yarn is then woven on looms into silk cloth by the weavers. 6.3 Different Varieties of silk Some of the varieties of silk are: Mulberry silk; Tassar silk; Mooga silk; Kosa silk; and Eri silk. Natural Silk and Artificial Silk We can distinguish between natural silk and artificial silk by performing the ‘burning test’. (i) The fabric which burns giving a smell of burning hair will be natural silk (or pure silk).

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(ii) The fabric which burns giving a smell of burning paper will be artificial silk (or rayon). Just like silk, wool is also made of proteins. So, a piece of wool also burns giving the smell of burning hair.

Discovery of Silk

The discovery of silk was made in China a long time back. The empress found some white worms eating up mulberry leaves. She also noticed that these worms were spinning shiny cocoons around them. A cocoon dropped into her cup of tea accidently and delicate silk threads separated from the cocoon. This is how silk was discovered. The discovery of silk led to the beginning of silk industry in China. China leads the world in silk production. India is also among the leading silk producing countries of the world. In India, a large number of women are engaged in various activates related to silk production such as rearing of silkworms, reeling of silk from cocoons and processing of raw silk into fabrics.

7. SYNTHETIC FIBRES

The man-made fibres produced from chemical substances are called synthetic fibres. A synthetic fibre is a polymer made from the molecules of a monomer (or sometimes two monomers) joined together to form very long chains.

A polymer is a ‘very big molecule’ formed by the combination of a large number of small molecules. The small molecules (of chemical compounds) which join together to form a polymer are called ‘monomers’. The monomers which make a polymer may all be of the ‘same compound’ or of ‘two different compounds’. The

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word ‘polymer’ comes from two Greek words ‘poly’ meaning ‘many’ and ‘mer’ meaning ‘units’. So, a polymer is made of many small ‘repeating units’ (of chemical compounds) called monomers.

Polymers are of two types : (i) Natural polymers (ii) Synthetic polymers.

7.1 Types of Synthetic Fibres

Depending upon the type of chemicals used for manufacturing synthetic fibres, there are four major types of synthetic fibres (or man-made fibres). These are :

(i) Rayon (ii) Nylon (iii) Polyester, and (iv) Acrylic.

Rayon is a man-made fibre made from a natural material called cellulose (obtained from wood pulp). Nylon, polyester and acrylic are fully synthetic fibres which do not require a natural material (like cellulose) for their manufacture. Wood pulp is a soft, wet mass of fibres obtained from wood. Wood pulp contains large amount of natural polymer called ‘cellulose’.

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Fibre to Fabric3MULTIPLE CHOICE QUESTIONS

1. The rearing of silkworms for obtaining silk is called

(a) cocoon

(b) silk

(c) sericulture

(d) silviculture

2. Which of the following is not a type of silk?

(a) Mulberry silk

(b) Tassar silk

(c) Mooga silk

(d) Moth silk

3. Paheli wanted to buy a gift made of animal fibre obtained

without killing the animal. Which of the following would be

the right gift for her to buy?

(a) Woollen shawl

(b) Silk scarf

(c) Animal fur cap

(d) Leather jacket

4. Silk fibre is obtained from

(a) fleece of sheep

(b) cotton ball

(c) cocoon

(d) shiny jute stalk

5. Wool fibre cannot be obtained from which of the following?

(a) Goat

(b) Llama

(c) Alpaca

(d) Moth

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16 EXEMPLAR PROBLEMS

6. Selective breeding is a process of

(a) selecting the offsprings with desired properties.

(b) selecting the parents with desired properties.

(c) selecting an area for breeding.

(d) selecting fine hair for good quality wool.

7. The general process that takes place at a sheep shearing shed is

(a) removal of fleece.

(b) separating hair of different textures.

(c) washing of sheep fibre to remove grease.

(d) rolling of sheep fibre into yarn.

8. The term sericulture is used for

(a) culture of bacteria.

(b) rearing of silkworm.

(c) making silk fabric from silk yarn.

(d) production of sarees.

9. Reeling of silk is

(a) a process of making silk reels.

(b) spinning of silk fibres.

(c) weaving of silk cloth.

(d) the process of taking silk threads from cocoon.

10. Silkworms secrete fibre made of

(a) fat

(b) cellulose

(c) protein

(d) nylon

VERY SHORT ANSWER QUESTIONS

11. Fill in the blanks in the following statements.

(a) _________ and _________ fibres are obtained from animals.

(b) Silk fibres come from _________ of silk _________.

(c) Wool yielding animals bear _________ on their body.

(d) Hair trap a lot of _________, which is a poor _________ of

heat.

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12. State whether the following statements are True or False. If

false, correct them.

(a) Silkworms are caterpillars of silk moth.

(b) In India, camels and goats are generally reared for

obtaining wool.

(c) The rearing of silkworms for obtaining silk is called

silviculture.

(d) In the process of obtaining wool from fleece, sorting is

done after scouring.

(e) Yak hair are not used to make woollen fabric.

13. How do the hair of certain animals help in keeping their bodies

warm?

SHORT ANSWER QUESTIONS

14. Match the items of Column I with the items given in

Column II.

15. Various steps involved to obtain wool from fleece are given here.

(i) Picking out the burrs

(ii) Dyeing in various colours

(iii) Shearing

(iv) Scouring

(v) Sorting

Write the above steps in the correct sequence in which they are

carried out.

FIBRE TO FABRIC

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18 EXEMPLAR PROBLEMS

16. Some words related with silk are jumbled up. Write them in

their correct form.

(a) TURECULRISE

(b) WILSMORK

(c) BELMURRY

(d) RINGLEE

17. Figure 3.1 shows three rings of circles with letters in them.

Some of these letters in each ring can form the name of one

wool yielding animal. Find the names of these animals.

Fig. 3.1

18. Write a caption for each of the figures given as Figure 3.2 (a–d).

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Fig. 3.2

19. Steps for the production of silk are given below in a jumbled

order. Arrange them in their proper sequence.

(a) Eggs are warmed to a suitable temperature for the larvae

to hatch from eggs.

(b) Fibers are taken out from the cocoon.

(c) After 25 to 30 days, the caterpillars stop eating and start

spinning cocoons.

(d) The larvae/caterpillars or silkworms are kept in clean

trays along with freshly chopped mulberry leaves.

(e) Female silk moths lay eggs.

(f) Cocoons are kept under the sun or boiled in water.

20. A wholesale woollen fibre dealer gets the woollen fibre of

different textures sorted for various purposes. Match the items

in Column I with the woollen fibre in Column II.

(c) (d)

FIBRE TO FABRIC

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20 EXEMPLAR PROBLEMS

LONG ANSWER QUESTIONS

21. Complete the paragraph related to the life history of silk moth

by filling in the blanks.

The ____(a)___ silk moth lays ___(b)___, from which hatch

____(c)___ called ___(d)____ or ___(e)____. They grow in size and

when the caterpillar is ready to enter the next stage of its life

history called ___(f)____, it first weaves a covering to hold itself,

which is known as ___(g)____.

22. Paheli went to the market to buy sarees for her mother. She

took out a thread from the edge of the two sarees shown by the

shopkeeper and burnt them. One thread burnt with a smell of

burning hair and the other burnt with the smell of burning

paper. Which thread is from a pure cotton saree and which

one from a pure silk saree? Give reason for your answer.

23. Explain the phrase – “Unity is Strength” on the basis of the

making of fabric from fibre.

24. Write various steps for processing fibres into wool.

25. Describe the life history of silk moth with the help of figures of

various stages.

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103ANSWERS

ANSWERS

MULTIPLE CHOICE QUESTIONS

1. (c) 2. (d) 3. (a) 4. (c)

5. (d) 6. (b) 7. (a) 8. (b)

9. (d) 10. (c)

VERY SHORT ANSWER QUESTIONS

11. (a) silk, wool (b) cocoons, moth

(c) hair (d) air, conductor

12. (a) True

(b) False, generally sheep are reared.

(c) False, it is sericulture.

(d) True

(e) False, used to make woollen fabric.

13. Hair traps a lot of air, which is a poor conductor of heat.

SHORT ANSWER QUESTIONS

14. (a) (iii); (b) (iv); (c) (ii); (d) (i)

15. Correct sequence is – (iii), (iv), (v), (i), (ii)

16. (a) sericulture (b) silkworm

(c) mulberry (d) reeling

17. Yak, Camel, Sheep

18. (a) Eggs of silk moth on mulberry leaves

(b) Silkworm

(c) Cocoon

(d) Cocoon with developing moth

19. Correct order – (e), (a), (d), (c), (f), (b)

20. (a) (iii); (b) (i); (c) (ii); (d) (iv)

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104 EXEMPLAR PROBLEMS

LONG ANSWER QUESTIONS

21. (a) female (b) eggs (c) larvae

(d) caterpillars (e) silkworms (f) pupa

(g) cocoon

22. The thread which burns with a smell of burning hair is from

pure silk. Silk and hair are protein fibres. Cotton and paper

both are carbohydrates, and on burning they give similar smell.

23. Hint: Fabric needs more energy to tear apart as compared to a

single fibre.

24. Hint: Write briefly about (i) shearing, (ii) scouring, (iii) sorting

(iv) picking out of burrs from the hair, (v) dyeing of fibres, (vi)

straightening, combing of fibres and rolling into yarm.

25. Hint: Trace life history of silk moth from eggs – larvae – pupa

– moth (Fig. 3.9 a – f of Class VII Science Textbook, NCERT)

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