What is Wool Structure Composition Properties and Uses
Wool is a kind of fibre obtained from hairs of sheep, goat, yak, and some other animals. From the definition, it is clear that wool can be obtained from many animals, not only from sheep. The clothes that we wear are cotton, silk, nylon, and wool. These fabrics are obtained from the fibres. These are naturally available to us or are man-made. The basic unit of any kind of fabric is fibre. Let’s discuss the fibre in more detail.
Types of Fibre
On the basis of origin, fibre can be divided into two types:
Natural Fibres
The origin of this fibre is natural. It can be further classified into various types:
Plant fibres
Animal fibres
Mineral fibres
Man-Made Fibre
These are synthetic fibres. These fibres can be further classified into a different subgroup:
Regenerated fibres
Synthetic fibres
Metallic fibres
Let’s discuss the Main Fibres
Plant Fibre
This is the type of fibre that are obtained from plants. For example- cotton and flax.
Animal Fibre
This type of fibre is obtained from animals. For example- silk and wool.
Synthetic Fibre
This type of fibres are manufactured in industries. These are called man-made fibres. For example- nylon, polyester.
Types of Wool
Sheep wool is obtained from sheep and it is commonly used and famous in Tibet and Ladakh. Angora wool is obtained from angora goat and it is commonly used in the hilly region like Jammu and Kashmir. The underfur of the angora goat is used in making fine shawls known as pashmina shawls.
The fur of many other animals is used in making fibre like a camel. Fur or camel, alpaca, llama etc is used in making fibre. In India the famous and common source of wool is sheep.
The quality and the quantity of the wool depends on the breed of the sheep. Some breeds of sheep have fine hair while others have coarse hairs.
Types of Sheep Hair
There are two forms of sheep hair present:
Coarse beard Hair
The Fine Soft under Hair Close to the Skin
Wool is obtained from this type of sheep hair. This type of hair is very fine. Therefore, used in making wool fibres. We see that sheep are the main source of wool. We need to produce good quality wool-producing sheep. For this, we perform selective breeding.
What is selective breeding? Selective breeding is the process of selecting parents for obtaining special characters in their offspring. So, for obtaining wool we need sheep with more soft hairs and less coarse hairs. In the Manufacturing process of wool, the selective parents will be the sheep with soft fine under hairs.
The Manufacturing Process of Wool
The manufacturing process of wool involves four steps. These steps are given below:
Shearing
Scouring
Sorting
Fabric production
Let’s Discuss Each Step One by One
Shearing
It is done manually by using a pair of scissors or electrically driven shavers. In this process when hairs are removed from the live sheep, known as clipped wool. When it is obtained from dead sheep it is known as pulled wool.
Scouring
The sheared skin with hairs is thoroughly washed in large tanks to remove grease, dirt, and dust. This process is known as souring.
Sorting
The hairy skin is sent to industries where hairs with various textures are separated or sorted. The small fluffy fibres are called burrs. These burrs are picked out from the hair. The people involved in this process generally get infected by the bacteria called Bacillus anthracis. This disease is called sorter’s disease.
Flowchart of the Manufacturing Process of Wool
The fur or the skin of the sheep (generally sheep)
Shearing (removal of thin dead skin layer)
Scouring (removed skin is washed in a large industrial tank to remove grease, oil, dirt and other kinds of contaminants.)
Sorting (hair of various texture is separated)
Removal of burrs (small fluffy fibres)
Dyeing of the processed wool (adding different colours)
Rolling into yarn
Parameters for measuring Quality of Wool
The quality of wool can be analysed using the following criteria.
The thickness of the fibre- The thinner the fibre, the better the quality of the wool is.
Waviness- A wool of good quality is more crimpy than inferior wool.
Fibre length- the good quality of wool has a short fibre length.
Uses of Wool
Wool is used in weaving sweaters.
Wool has been used for making carpets.
Wool is used in making wool felt. These are used for absorbing noises coming from heavy machines and stereo speakers.
Did You Know?
Wool has the ability to absorb moisture.
Wool does not burn over the flame but smoulders.
Wool is a lightweight fabric.
We do not need to iron wool regularly as wool does not wrinkle easily.
Wool fabrics are resistant to dirt.
FAQs on Wool as a Natural Protein Fibre in Chemistry
1. What is wool in chemistry?
Wool is a natural protein fibre mainly composed of the structural protein keratin. In chemistry, wool is classified as a biopolymer made of long chains of amino acids linked by peptide bonds (–CONH–). It is obtained from animal hair, especially sheep, and contains elements such as carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). The sulfur comes from the amino acid cysteine, which forms disulfide bonds that give wool strength and elasticity.
2. What is the chemical composition of wool?
Wool is chemically composed of the protein keratin, which is a polymer of amino acids containing C, H, O, N, and S. Its structure includes:
- Peptide bonds (–CONH–) linking amino acids
- Disulfide bonds (–S–S–) from cysteine residues
- Hydrogen bonds and ionic interactions
These cross-links make wool strong, elastic, and resistant to mild chemicals compared to many other natural fibres.
3. Is wool a polymer?
Yes, wool is a natural polymer because it consists of long chains of repeating amino acid units joined by peptide bonds. The polymer in wool is keratin, which forms through condensation reactions between amino acids:
- Amino acid 1 + Amino acid 2 → Dipeptide + H2O
Since many amino acids link together to form long chains, wool is classified as a biopolymer in polymer chemistry.
4. Why does wool contain sulfur?
Wool contains sulfur because it has the amino acid cysteine, which forms disulfide bonds (–S–S–) in keratin. These sulfur–sulfur bonds:
- Cross-link protein chains
- Increase strength and elasticity
- Improve resistance to deformation
When wool burns, the presence of sulfur produces a characteristic smell similar to burning hair, confirming its protein nature.
5. Why does wool shrink in hot water?
Wool shrinks in hot water due to denaturation and tightening of its protein structure. Heat and agitation:
- Break hydrogen bonds in keratin
- Cause fibre scales to interlock (felting)
- Lead to irreversible shrinkage
This process, called felting, makes wool fibres mat together, reducing the fabric size.
6. Is wool acidic or basic in nature?
Wool is amphoteric, meaning it can react with both acids and bases. This is because wool contains:
- –NH2 (basic amino groups)
- –COOH (acidic carboxyl groups)
In acidic solutions, wool becomes positively charged, and in basic solutions, it becomes negatively charged. This property allows wool to absorb dyes effectively in textile chemistry.
7. What happens when wool is treated with acids or bases?
Wool is relatively resistant to dilute acids but damaged by strong bases due to hydrolysis of peptide bonds. Specifically:
- Dilute acids: Wool remains stable and can even be dyed.
- Strong bases (alkalis): Break peptide bonds (–CONH–), degrading keratin.
This is why wool fabrics should not be washed with strong alkaline detergents.
8. How is wool different from cotton in chemical composition?
Wool is a protein fibre (keratin), while cotton is a carbohydrate polymer (cellulose). The key chemical differences are:
- Wool contains C, H, O, N, S; cotton contains only C, H, O.
- Wool has peptide bonds; cotton has β-1,4-glycosidic bonds.
- Wool is amphoteric; cotton is neutral.
These differences explain why wool reacts differently to heat, acids, and bases compared to cotton.
9. Why does wool burn with the smell of hair?
Wool burns with a hair-like smell because it is made of the protein keratin, similar to human hair. When heated:
- Peptide bonds decompose
- Sulfur compounds are released
- A characteristic burning hair odor is produced
Unlike synthetic fibres, wool burns slowly and often self-extinguishes due to its nitrogen and sulfur content.
10. What are the main chemical properties of wool?
The main chemical properties of wool arise from its protein structure and cross-linked keratin chains. These include:
- Amphoteric nature (reacts with acids and bases)
- Presence of peptide bonds (–CONH–)
- Strong disulfide cross-links (–S–S–)
- Biodegradability as a natural polymer
- Resistance to mild acids but sensitivity to strong alkalis
These properties make wool important in textile chemistry, polymer science, and material studies.
