Fibre to Fabric Class-7 Science(Chap-3)

                                           Fibre to Fabric                     Class-7     Science(Chap-3) NCERT

Ø  Silk comes from silkworms and wool is obtained from the sheep, goat, yak and some other animals. Hence, silk and wool are animal fibres.

Ø  The hairy skin of the sheep has two types of fibres that form the fleece: (i) the coarse beard hair and (ii) the fine soft under-hair close to the skin. The fine hair provide the fibres for making wool.

Ø  Some breeds of sheep possess only fine under-hair. The process of selecting sheep parents for obtaining special characters in their offspring is known as ‘selective breeding’.

·         Animals that yield wool

Ø  Sheep - Its wool is generally used in clothing production and commonly available in the market.

Ø  Goats- Mohair and Cashmore come from goats. Mohair is obtained from Angora goats which is known for its lusture, used for clothing and shawls and fine yarn cashmore comes from the cashmore goats and is considered as the most luxurious of all types of wool. These goats are found in hilly regions such as Jammu and Kashmir. It is woven into fine shawls called Pashmina shawls.

Ø  Yak- yak wool produced from the coat hair of yaks. These  are common in Tibet and Ladakh.

Ø  Lamas – The Lama genus of animals originate in South America includes Llama and Alpaca. Lamas are generally reared to produce coarse wool that includes stiff guard hairs. The Alpacas are the most common for fibre production. The fine Alpaca wool does not contain guard hairs and used to spin fine yarns.

Ø  Camels – Camel hair is most commonly produced in Inner Mongolia and other parts of China. The wool of  camels is used to produce fine textiles including scarves, gloves and jackets.

Ø  Rabbits – Angora Rabbits can produce about 3 pounds of wool per year. Its hair is used to make sweaters, gloves and scarves.

Ø  Certain breeds of sheep(selective breeds) have thick coat of hair on their body which yields good quality of wool in large quantities.

Ø  Once the reared sheep have developed  a thick growth of hair, hair is shaved off for getting wool.

Ø  The process of removing the fleece of the sheep along with a thin hair from its body is called Shearing.

Ø  After shearing the hair or the woolen fibre of the sheep are processed to obtain woolen yarn.

Ø  When the sheared skin with hair is roughly washed in tanks to remove grease, dust and dirt, it is called Scouring.

Ø  After Scouring, the hairy skin is sent to a factory where hair of different textures are separated. This process is called Sorting.

Ø  After sorting, the small fluffy fibres called burrs, are picked out from the hair. The fibres are scoured again and dried.

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

Ø  Finally, 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 woolen cloth.  

Ø  The processing of fibre into wool can be represented as follows:

Shearing-------Scouring--------Sorting--------Cleaning of burrs------Dyeing-------Rolling

·         Silk

Ø  The rearing of silkworms for obtaining silk is called Sericulture.

Ø  The female silk moth lays eggs, from which hatch larvae which are called Caterpillars or Silkworms.

Ø  Caterpillers or silk worms grow in size and when it is ready to enter the next stage of its life history, it is called Pupa.

Ø  The Pupa first weaves a net to hold itself. Then it swings its head from side to side in the form of the figure eight(8). During these movements, the caterpillar secretes fibre made of a protein which hardens and becomes silk fibre.

Ø  When the caterpillar completely covers itself by silk fibre and turns into pupa(covering) is known as  Cocoon. The further development of the pupa into moth continues inside the cocoon.

Ø  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, Tasar silk, Mooga silk, Kosa silk etc. spun by different types of moths.

Ø   The most common silk moth is the Mulberry moth which is soft, lustrous and elastic and can be dyed in beautiful colours.

·         From Cocoon to Silk

Ø  For obtaining silk, moths are reared and their cocoons are collected to get silk threads.

Ø  A female silk moth lays hundreds of eggs at a time. These are stored carefully and given to silkworm farmers. The eggs are kept under suitable conditions of temperature and humidity for the larvae to hatch from eggs. This is done when mulberry tree bear a fresh crop of leaf.

Ø  The larvae, called caterpillars are kept in clean bamboo trays along with freshly chopped mulberry leaves. The caterpillar spins the cocoon inside which develops the silk moth.

Ø  A pile of cocoons is used for obtaining silk fibre. The cocoons are kept under the sun, or boiled or exposed to stream to separate the silk fibres.

Ø  The process of taking out threads from the cocoon for use as silk is called ‘reeling the silk’.

Ø  Reeling is done  in special machines, which unwind the threads or fibres of silk from the cocoon.