Introduction to the Topic
Welcome to NCERT Explained! In our daily lives, we wear various kinds of clothes made from different materials. Have you ever wondered where these materials come from? In Class VI, you learned about obtaining fibres from plants. Now, in Class VII Science, Chapter 3 - Fibre to Fabric, we dive deeper into animal fibres, specifically wool and silk, and learn how raw materials are transformed into the cozy sweaters and soft sarees we wear.
Key Concepts Explained
Let us break down the essential concepts of animal fibres, their sources, and the steps involved in processing them into usable fabrics.
1. Wool: From Fleece to Fibre
Wool is obtained from the fleece (hair) of sheep, goats, yaks, and some other animals. These wool-yielding animals have a thick coat of hair on their bodies because hair traps a lot of air. Since air is a poor conductor of heat, it keeps these animals warm during cold winters.
- Breeding for Wool: Parents are specially chosen to give birth to sheep that have only soft under-hair. This process of selecting parents for obtaining special characters in their offspring is called selective breeding.
- Processing Fibres into Wool: The transformation of wool involves several distinct steps:
- Shearing: The fleece of the sheep along with a thin layer of skin is removed from its body using specialized clippers.
- Scouring: The sheared skin with hair is thoroughly washed in tanks to remove grease, dust, and dirt. This is called scouring.
- Sorting: After scouring, hair is sent to a factory where hair of different textures is separated or sorted.
- Cleaning burrs: The small fluffy fibres, called burrs, are picked out from the hair. These are the same burrs that sometimes appear on your sweaters.
- Dyeing: The fibres are dyed in various colors because the natural fleece of sheep and goats is black, brown, or white.
- Rolling: Finally, the fibres are straightened, combed, and rolled into yarn. The longer fibres are made into wool for sweaters, and the shorter ones are spun and woven into woolen cloth.
3. Silk: The Secret of Silkworms
Silk is another important animal fibre. Silk fibres are drawn from the cocoons of the silk moth. The rearing of silkworms for obtaining silk is called sericulture.
- Life Cycle of the Silk Moth:
- The female silk moth lays eggs, from which hatch larvae called caterpillars or silkworms.
- The caterpillars grow in size and feed on fresh mulberry leaves day and night.
- When ready to enter the next stage of its life history called pupa, the silkworm first weaves a net to hold itself. Then it swings its head from side to side in the form of the figure of eight (\(8\)).
- During these movements of the head, the caterpillar secretes fibre made of a protein which hardens on exposure to air and becomes silk.
- Soon the silkworm completely covers itself by silk fibres and turns into a pupa. This covering is known as the cocoon.
- The further development of the pupa into a moth continues inside the cocoon. Silk yarn is obtained from the spun cocoons of silk moths.
From Cocoon to Silk Fabric
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.
Summary & Key Takeaways
- Fabrics are made from fibres, which are obtained from natural or artificial sources.
- Animals such as sheep, goats, and camels yield wool. The process involves shearing, scouring, sorting, cleaning burrs, dyeing, and spinning.
- Silk is a protein fibre obtained from the cocoons of the silkworm (Bombyx mori).
- The rearing of silkworms for silk production is called sericulture.
- Understanding these natural processes helps us appreciate the engineering behind the clothing we wear every day.
