5 February 2014

Animal Fibre - Silk

Animal Fibre - Silk : Science CBSE Notes

Silk is the queen of iles. It is an animal fibre produced by the silkworm to build its cocoon

Discovery Of Silk
Silk was discovered in China, when empress Si-lung-Chi was worried about the damaged mulberry leaves in her garden. Emperor Huang-ti found that white worms were eating up the mulberry leaves and spinning shiny cocoons. 
Silk, Discovery of Silk, NCERT Notes, CBSE NotesSilkworms are not worms actually, but the larvae or caterpillars that have hatched from the eggs of the silk moth. 

Different types of silk moths yield different types of silk yarn, such as:
  • Tassar silk
  • Moonga silk
  • Kosa silk
Silk is the strongest of all natural fibres. A soft silk yarn is as strong as a comparable thread of steel. 
Sericulture, or silk farming, is the rearing of silkworms for the production of raw silk.
  • The female silk moth lays hundreds of eggs. These are stored on strips of cloth or paper.
  • The eggs are then sold to silkworm farmers, who rear them under specific hygienic conditions.
  • When the mulberry tree bears a fresh crop of leaves, the eggs are warmed suitably so that the larvae hatch from them.
  • The larvae, caterpillars or silkworms are then stored in clean bamboo trays and are fed freshly chopped mulberry leaves. They eat day and night, and grow to enormous sizes.
  • The bamboo trays are provided with small racks or twigs to which the cocoons can be attached.
  • This happens usually 25 to 30 days later, when the caterpillars stop feeding and move to the twigs to spin cocoons. The silk moth develops inside these cocoons.
  • As caterpillars eat and grow bigger, they also shed their skin. Underneath the old one is a new skin. Caterpillars may shed skin four or five times.
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Procedure of Extracting silk from the cocoon:
  • The first step is to separate the silk fibre from the cocoon. For this, they need to be exposed to warmth.
  • Piles of cocoons are kept under the sun, boiled or exposed to steam. The warmth causes the silk fibre to separate from the rest of the cocoon.
  • The next step is called reeling the silk, which is the process of delicately unwinding the fibre from the cocoon. These silk filaments are soft, and 300 to 900 metres long.
  • Reeling is also done in special machines.
  • The silk thread is then bleached and dyed into many shades.
  • The silk fibre is now spun into silk thread, which is then woven into silk cloth by weavers.
In our country, women are involved in a big way in the sericulture industry. They contribute to processes of rearing of silkworms, reeling of silk from cocoons, and processing of raw silk into fabric. 

This enterprise contributes to the nation’s economy and also helps rank India among the leading silk producing countries. Of course, China leads the world in silk production.

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