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CBSE Class 7 Chemistry Notes- Chapter 1 Fibre to Fabric

The fibres that are obtained from animals are called animal fibres.
We get wool from animals like sheep, goat, yak, etc. These animals have a thick coat of hair which traps a lot of air and hence keeps the animals warm as air is a poor conductor of heat.
There are two types of fibres obtained from the sheep:
(i) Coarse beard hair
(ii) fine, soft under-hair close to the skin
The fine hair is used to make wool. There are sheep which have only fine under-hair. Such sheep are a result of ‘selective breeding’ in which the parent6s are specifically chosen to give birth to such sheep. Animals that yield wool are yak, sheep, Angora goats, Llama, alpaca, camels, etc.

  • The sheep are reared and bred. Shepherds take care of them.
  • The fleece of the sheep is removed from its body. This process is called shearing. Shearing also removes a thin layer of skin but it is painless.
  • The sheared skin and hair is washed to remove the grease and dirt. This process is called scouring.
  • Sorting is done after scouring. In sorting, the hairs of different textures are separated in factories.
  • From the hair, burrs are removed. Burrs are small fluffy fibres. The fibres are scoured again and left to dry.
  • The fibres are then dyed to give them colour.
  • The fibres are then rolled into yarns after straightening them.
  • These fibres are then woven and are used to make woolen clothes.

Silk is obtained from silkworms. ‘Sericulture’ is the name given to the process of rearing silkworms for obtaining silk.
It is the female silk moth that lays eggs. When these eggs hatch, a larva comes out which is called a ‘caterpillar’ or ‘silkworm’. When the caterpillar grows and enters the next stage of its life cycle, which is called ‘pupa’, it weaves a net to hold itself. It secretes a silk fibre and covers itself with it. This covering is called ‘cocoon’.it is from the cocoon that the silk yarn is obtained. Mulberry silk moth is the most common silk moth.

  • Rearing silkworms: A female silk moth lays hundreds of eggs at a time which are stored and sold to the farmers who take care of them. The eggs then hatch and the silkworm grows and then forms the cocoon.
  • Processing silk: The cocoons are kept under the sun or boiled and then they are separated out. This process where the threads are taken out from the cocoon is called ‘reeling’ of the silk. These fibres are the spun or woven into silk cloth.

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