Class 7 – Science – Notes – Chapter 3 – Fibre to Fabric

Introduction to Wool and Its Importance

Wool is a natural animal fiber that plays a key role in the textile industry. It is soft, insulating, and ideal for making winter clothes. Unlike plant fibers like cotton, wool is obtained from the hair of certain animals, such as sheep, goats, rabbits, camels, and yaks. Wool is known for its ability to trap air, which provides warmth.

How Wool Is Obtained – Step-by-Step Process

The transformation from animal fleece to woolen yarn involves multiple steps, each essential to prepare the wool for fabric-making:

Shearing

• Definition: Shearing is the removal of fleece (the hairy coat) from animals, usually once a year.
• Process: It is done using mechanical clippers, much like a haircut.
• Note: Shearing is painless for the animal and is generally performed in spring so the animal can stay cool in summer.

 Scouring

• Definition: Scouring is the process of washing the sheared wool to remove dirt, sweat (suint), oil (lanolin), and other impurities.
• Method: Wool is cleaned in large tanks using hot water and detergent.
• Importance: This step ensures the wool is hygienic and suitable for spinning.

Sorting

• Definition: Sorting involves separating wool fibers based on their texture, length, and quality.
• Example: Wool from the shoulders and sides of a sheep is finer than that from the legs or belly.

Burr Picking

• Definition: Burrs are small vegetable particles such as dried leaves or twigs stuck in the fleece.
• Process: Workers hand-pick these burrs to purify the wool.
• Impact: This improves the texture and feel of the final woolen fabric.

 Dyeing

• Definition: Dyeing is the process of adding color to the wool.
• Method: Wool is dyed using chemical or natural dyes depending on the requirement.

 Straightening, Combing, and Spinning

• Straightening: The fibers are straightened using rollers.
• Combing: Fibers are aligned in the same direction to remove knots or short fibers.
• Spinning: Finally, the combed wool is spun into yarn using machines. The yarn can then be woven into fabric.

Animals That Yield Wool

Wool is not obtained only from sheep. Other animals also produce types of wool suited for various purposes.

Animal	Wool Type	Notes
Sheep	Wool	Most common
Angora Goat	Mohair	Soft, lustrous
Cashmere Goat	Cashmere	Very fine and soft
Yak	Yak wool	Found in Ladakh and Tibet
Llama and Alpaca	Llama wool, Alpaca wool	Native to South America
Angora Rabbit	Angora wool	Extremely soft and silky
Camel	Camel wool	Warm, used in desert regions
Musk Ox	Qiviut	One of the softest and rarest wools

🇮🇳 Indian Breeds of Wool-Producing Sheep

India is home to several sheep breeds adapted to diverse climates and terrains. Each breed provides wool with unique characteristics:

• Deccani Sheep: Found in Maharashtra; produces coarse wool.
• Mandya Sheep: Native to Karnataka; used for carpet wool.
• Nellore Sheep: From Andhra Pradesh; raised for meat and moderate wool.
• Marwari Sheep: From Rajasthan; provides good quality wool.
• Coimbatore Sheep: Tamil Nadu-based breed, local utility.
• Trichy Black Sheep: Found in Tamil Nadu; regional breed.
• Vembur Sheep: Tamil Nadu origin; known for its hardiness.

Occupational Hazard – Sorter’s Disease (Anthrax)

• Problem: Workers who handle wool may get infected by Bacillus anthracis, a bacterium found in animal hides or wool.
• Disease: The infection caused is called Anthrax or “Sorter’s Disease”.
• Effect: It can cause a severe and sometimes fatal blood infection.
• Precaution: Workers must use protective equipment like gloves and masks while sorting wool.

 Polymers – Classifying Fibres

Polymers are long-chain molecules made up of repeating units called monomers. Fibers are classified based on the source and chemical composition.

1️⃣ Natural Polymers

• Origin: From plants and animals.
• Examples: Wool, Silk, Jute, Cotton, Natural Rubber.

2️⃣ Semi-Synthetic Polymers

• Definition: Modified natural polymers to improve properties.
• Examples: Acetate Rayon, Viscose Rayon.

3️⃣ Synthetic Polymers

• Definition: Fully man-made polymers produced in laboratories or industries.
• Examples: Nylon, Polyester, Acrylic, Plastic.

Silk – Nature’s Luxury Fibre

Silk is a protein-based natural fibre produced by the larvae of certain moths. It is smooth, shiny, and highly valued for its softness and elegance.

• Composition: Silk is made of fibroin (protein), secreted in liquid form by the silkworm.
• Use: Silkworms spin this secretion to form protective cocoons.

 What is Sericulture?

Sericulture refers to the scientific practice of raising silkworms for silk production.

• Scale: It is practiced globally and supports many small-scale farmers.
• Products: Different types of silk are produced such as:
  • Mulberry Silk (Best quality, softest)
  • Tassar Silk (Golden color, tribal areas)
  • Muga Silk (Exclusive to Assam, golden-yellow)
  • Eri Silk (Strong, warm, sustainable)

 About Mulberry Silkworm – Bombyx mori

• Feeds only on mulberry leaves.
• White in color, about 2.5 cm in length.
• Produces the highest quality silk.

Lifecycle of a Silk Moth

Silkworms pass through 4 key life stages:

1. Egg – Tiny, laid by the female moth.
2. Larva (Silkworm) – Feeds on mulberry leaves, grows quickly.
3. Pupa – Silkworm spins a cocoon from silk thread.
4. Adult (Imago) – Moth emerges from the cocoon.

From Cocoon to Silk Thread

• After pupation, cocoons are collected.
• Boiling: Cocoons are boiled in hot water to dissolve the gummy substance.
• Thread Extraction: Threads from 4 to 8 cocoons are pulled together into one long strand.
• Reeling: The combined thread is wound on reels.
• Processing: These raw silk threads are washed, dyed, and woven into fabric.

Silk Reeling – Making Thread from Cocoon

Silk reeling is the mechanical process where threads are unwound from boiled cocoons and combined to form a single continuous silk yarn.

• Method: Reeling is done in warm water to soften the silk.
• Machine: A fast-moving reel collects the filaments and spins them into thread for weaving.