CBSE – 7th Standard Science

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Chapter 3 – Fibre to Fabric

FIBRE TO FABRIC

  • Wool comes from sheep, goat, yak and some other animals.
  • These wool-yielding animals bear hair on their body.
  • Hair trap a lot of air. Air is a poor conductor of heat. So, hair keeps these animals warm.
  • Wool is derived from these hairy fibres.
  • The hairy skin of the sheep has two types of fibres that form its fleece
  • The coarse beard hair the fine soft under-hair close to the skin.
  • The fine hair provide the fibres for making wool.
  • Some breeds of sheep possess only fine under-hair.
  • Their parents are specially chosen to give birth to sheep which have only soft under hair.
  • This process of selecting parents for obtaining special characters in their offspring, such as soft under hair in sheep, is termed ‘selective breeding’.
  • Several breeds of sheep are found in different parts of our country
  • However, the fleece of sheep is not the only source of wool, though wool commonly available in the market is sheep wool
  • Yak wool is common in Tibet and Ladakh. Angora wool is obtained from angora goats, found in hilly regions such as Jammu and Kashmir.
  • Wool is also obtained from goat hair
  • The under fur of Kashmiri goat is soft.
  • It is woven into fine shawls called Pashmina shawls. The fur (hair) on the body of camels is also used as wool Llama and Alpaca, found in South America, also yield wool.
  • For obtaining wool, sheep are reared.
  • Their hair is cut and processed into wool.
  • If you travel to the hills in Jammu & Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh and Sikkim, or the plains of Haryana, Punjab, Rajasthan and Gujarat, you can see shepherds taking their herds of sheep for grazing.
  • Sheep are herbivores and prefer grass and leaves.
  • Apart from grazing sheep, rearers also feed them on a mixture of pulses, corn, jowar, oil cakes (material left after taking out oil from seeds) and minerals.
  • In winter, sheep are kept indoors and fed on leaves, grain and dry fodder. Sheep are reared in many parts of our country for wool.
  • Some breeds of sheep reared in our country for producing wool.
  • The quality and texture of the fibres obtained from them is also indicated in the table.
  • Certain breeds of sheep have thick coat of hair on their body which yields good quality wool in large quantities.
  • Once the reared sheep have developed a thick growth of hair, hair is shaved off for getting wool.
  • The wool which is used for knitting sweaters or for weaving shawls is the finished product of a long process, which involves the following steps:

 

  • The fleece of the sheep along with a thin layer of skin is removed from its body This process is called shearing.

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  • Machines similar to those used by barbers are used to shave off hair. Usually, hair are removed during the hot weather.
  • This enables sheep to survive without their protective coat of hair. The hair provide woolen fibers.
  • Woolen fibers are then processed to obtain woolen yarn.
  • Shearing does not hurt the sheep just as it does not hurt when you get a haircut or your father shaves his beard.
  • The uppermost layer of the skin is dead.
  • The sheared skin with hair is thoroughly washed in tanks to remove grease, dust and dirt. This is called scouring. Nowadays scouring is done by machines
  • After scouring, sorting is done.
  • The hairy skin is sent to a factory where hair of different textures are separated or sorted.
  • The small fluffy fibres, called burrs, are picked out from the hair.
  • These are the same burrs which sometimes appear on your sweaters. The fibres are scoured again and dried.
  • This is the wool ready to be drawn into fibres.

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  • The fibres can be dyed in various colours, as the natural fleece of sheep and goats is black, brown or white.

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  • The fibres are straightened, combed and rolled into yarn.
  • The longer fibres are made into wool for sweaters and the shorter fibres are spun and woven into woollen cloth.

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  • Wool industry is an important means of livelihood for many people in our country. But sorter’s job is risky as sometimes they get infected by a bacterium, anthrax, which causes a fatal blood disease called sorter’s disease.
  • Such risks faced by workers in any industry are called occupational hazards.
  • The female silk moth lays eggs, from which hatch larvae which are called caterpillars or silkworms.
  • They grow in size and when the caterpillar is ready to enter the next stage of its life history called pupa, it first weaves a net to hold itself.

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  • Then it swings its head from side to side in the form of the figure of eight.
  • During these movements of the head, the caterpillar secretes fibre made of a protein which hardens on exposure to air and becomes silk fibre.
  • Soon the caterpillar completely covers itself by silk fibres and turns into pupa. This covering is known as cocoon.

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  • The further development of the pupa into moth continues inside the cocoon.
  • Silk fibres are used for weaving silk cloth.
  • The silk yarn (thread) is obtained from the cocoon of the silk moth.
  • There is a variety of silk moths which look very different from one another and the silk yarn they yield is different in texture (coarse, smooth, shiny, etc.).
  • Thus, tassar silk, mooga silk, kosa silk, etc., are obtained from cocoons spun by different types of moths. The most common silk moth is the mulberry silk moth.
  • The silk fibre from the cocoon of this moth is soft, lustrous and elastic and can be dyed in beautiful colours.
  • Sericulture or culture of silkworms is a very old occupation in India. India produces plenty of silk on a commercial scale.
  • In India, women are significantly involved in various kinds of industries related to silk production.
  • These are rearing of silkworms, reeling of silk from cocoons and processing of raw silk into fabrics.
  • By their enterprise, they contribute to the nation’s economy.
  • China leads the world in silk production. India also ranks among the leading silk producing countries.
  • The exact time of discovery of silk is perhaps unknown.
  • According to an old Chinese legend, the empress Si-lung-Chi was asked by the emperor Huang-ti to find the cause of the damaged leaves of mulberry trees growing in their garden.
  • The empress found white worms eating up mulberry leaves.
  • She also noticed that they were spinning shiny cocoons around them.
  • Accidentally a cocoon dropped into her cup of tea and a tangle of delicate threads separated from the cocoon.

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  • Silk industry began in China and was kept a closely guarded secret for hundreds of years.
  • Later on, traders and travellers introduced silk to other countries.
  • The route they travelled is still called the ‘silk route’
  • The larvae are kept in clean bamboo trays along with freshly chopped mulberry leaves.
  • After 25 to 30 days, the caterpillars stop eating and move to a tiny chamber of bamboo in the tray to spin cocoons.
  • Small racks or twigs may be provided in the trays to which cocoons get attached.
  • The caterpillar or silkworm spins the cocoon inside which develops the silk moth.
  • A pile of cocoons is used for obtaining silk fibres.
  • The cocoons are kept under the sun or boiled or exposed to steam.
  • The silk fibres separate out. The process of taking out threads from the cocoon for use as silk is called reeling the silk.
  • Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon.
  • Silk fibres are then spun into silk threads, which are woven into silk cloth by weavers.

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