What Is Wool Fabric Composition Structure Properties and Uses Explained
Wool is a textile fibre made from sheep and other species, such as goats' cashmere and mohair, muskoxen's qiviut, rabbit’s angora, and camelid’s various forms of wool.
Wool fibre is a finely ordered structure with the cuticle, cortex, and medulla as its main histological components. Wool fibre is a natural fibre, and its characteristics such as diameter, crimps, and length are important parameters of the wool trait and indicators of the wool's spinning quality.
What is Fleece?
If you are wondering What is Fleece? If there is such a thing as a man-made wonder commodity, fleece it is. While being named after a sheep’s fleece coat, it is made entirely of synthetic materials and is derived from plastic rather than a fluffy sheep's coat.
Properties of Wool
Crimps: Wool fibre is wavy and twisted in some places. Crimp is the name for this waviness. The finer the yarn, the more crimps it will get.
Friction softens the wool fibre, particularly when wet, and is thus beneficial in maintaining a smooth, soft texture in fabrics.
The heat has little impact at low temperatures, but high temperatures weaken the fibre and cause it to lose its colour.
Moisture effect: Wool is the most hygroscopic material on the planet. It can absorb up to 50% of its weight and bear up to 20% of its weight without getting drenched.
When wool fibres are exposed to heat, moisture, and strain, they interlock and contract. Felting is aided by the scale-like exterior of the fibres.
Heat conductivity: Since wool fibre is a weak conductor of heat, fabrics made from it are best suited for winter wear.
Wool is highly durable, and when hung after being wrinkled or formed, it returns to its original form.
It has more strength than silk. Wool loses about 25% of its strength when wet. The yarn's strength will increase as the fibre lengthens.
Wool is a highly elastic material. When it's dry, it's about 10% to 30% stretched, and when it's wet, it's about 40% to 50% stretched. When it's dry, it quickly returns to its original measurements.
Wool has a high resistance to shrinkage. Long-term moisture exposure, on the other hand, can cause shrinkage.
Characteristics of Wool
Antistatic
Anti Wrinkle
Biodegradable
Breathable
Elastic
Fire resistant
Nature’s fibre
Odour resistant
Renewable
Stain-resistant
Soft
Processing Fibres Into Wool
Shearing – Shearing is the method of removing the woollen coat or fleece from an animal. Shearing instruments such as scissors, hand knives, and electric shears are used to do this without damaging the animal.
Scouring – Raw or grease wool is wool that has been taken directly from the sheep. To remove grease, dust, and dirt, raw sheared wool is washed in tanks with detergent and alkali.
Sorting and Grading – Defective or inferior wool is removed after scouring. Sorting is the term for this procedure. Grading is the method of sorting wool based on the weight, colour, and texture of the fibres.
Carding – Wool must be disentangled and washed until it can be used to make clothing. Continuous fibres are formed by separating the intermixed fibres.
Carded wool is twisted into a silver cord to make yarn. Silver is twisted and stretched into a thin thread. A mule spinning system is commonly used to spin woollen yarns.
Washing and Finishing – Woollen yarn is spun or knitted into fabric, which is then used to produce finished goods like clothing, tablecloths, and bags.
Types of Wool Fabric
Here mentioned are the types of wool fibres-
Lambswool is derived from the first shearing of a young sheep (lamb) at about seven months of age. It's also known as virgin wool, but that term also applies to wool that hasn't been processed yet. Shearing the lamb at this point produces wool that is exceptionally smooth, fluffy, and fine, as well as hypoallergenic.
Merino wool is derived from the merino sheep breed, which originated in Spain, though most merino wool is now exported from Australia. Merino wool is known for its fine fibres, which give it a supremely soft hand and make it ideal for garments that come into direct contact with the wearer's skin, such as base layers.
This wool is produced by Shetland sheep from Scotland's Shetland Islands. It's thicker and coarser than other wools, such as merino, due to the region's cold climate.
Mohair is a type of wool that comes from the Angora goat and differs from other types of wool for many reasons. In the shearing process, guard hairs from the goat's topcoat are often mixed in with the undercoat. Angora goats are grown in a mild environment, so their fibres aren't as coarse as other wools; their longer length gives the fibre its smoothness and results in a uniquely fluffy cloth.
When cashmere (Kashmir) goats join the moulting season, they have their undercoats shorn. Since cashmere is shorn from the undercoat, the yield per goat is low, so a single sweater needs two cashmere goats.
Angora wool is the lightest, best, and warmest of the natural fibres, coming from Angora rabbits. Angora fibres are hollow and smooth, similar to alpaca fibres, giving them unrivalled warmth and loft. The fibres are incredibly fine, but they are also extremely fragile. As a result, angora is often blended with other fibres to improve its longevity.
The majority of camel hair comes from Bactrian camels, which are born in cold climates such as Mongolia, China, and Russia, and is collected in the spring when the camel moults. Camel hair has a hollow appearance similar to mohair and is smoother and longer than sheep's fur. As a result, the fabric is lighter and lustrous than sheep's fur, and it's just as soft as cashmere.
The undercoat of the arctic muskox, which is bred in Canada and Alaska, is used to make Qiviut fur. The undercoat of the muskox is shed during the moulting season, and breeders either harvest the wool by combing it or plucking it from the grass. Qiviut is eight times colder than superfine sheep's wool and is finer than superfine sheep's wool. It also does not shrink when submerged in water.
Did You Know?
Alpacas are South American animals that grow hollow fur. Alpaca has a peculiar property that makes them both lightweight and insulating. It's both lighter and warmer than wool from sheep. Alpaca is comparable to cashmere in terms of softness, but it is much heavier. Alpaca hair is hypoallergenic by nature, making it perfect for those who have sensitive skin.
FAQs on Wool Fabric in Chemistry Structure Properties and Applications
1. What is wool fabric made of chemically?
Wool fabric is chemically composed of the protein keratin, which is a natural polymer made of amino acids. Wool fibers contain:
- Long chains of amino acids linked by peptide bonds
- High sulfur content due to the amino acid cysteine
- Disulfide bonds (–S–S–) that give wool strength and elasticity
2. What is the chemical structure of wool (keratin)?
The chemical structure of wool is a polypeptide chain formed by amino acids linked through peptide bonds (–CONH–). Each amino acid has the general structure:
- H2N–CHR–COOH
3. Why does wool shrink when washed in hot water?
Wool shrinks in hot water because heat and agitation disrupt hydrogen bonds and cause fiber scales to interlock in a process called felting. Chemically:
- Hot water weakens hydrogen bonds in keratin
- Agitation causes surface scales to mesh together
- New bonds form in a tighter arrangement
4. What type of polymer is wool?
Wool is a natural protein polymer composed of amino acid monomers. It is classified as:
- A biopolymer (naturally occurring polymer)
- A condensation polymer, formed by removal of water during peptide bond formation
5. What chemical bonds are present in wool fibers?
Wool fibers contain peptide bonds, hydrogen bonds, ionic bonds, and disulfide bonds. The main bonds include:
- Peptide bonds (–CONH–) linking amino acids
- Hydrogen bonds stabilizing the helix structure
- Disulfide bonds (–S–S–) providing strength and elasticity
- Ionic (salt) linkages between charged side groups
6. How does acid affect wool chemically?
Dilute acids generally do not damage wool significantly, but strong acids hydrolyze its peptide bonds. Chemically:
- Strong acids break peptide bonds via acid hydrolysis
- This converts the protein into smaller peptides or amino acids
R–CONH–R' + H2O → R–COOH + R'–NH2
This reaction weakens and degrades wool fibers.
7. How do alkalis affect wool fabric?
Alkalis damage wool more severely than acids because they break peptide bonds through alkaline hydrolysis. In basic conditions:
- –CONH– bonds are cleaved
- Protein structure is destroyed
- Fiber strength decreases rapidly
8. Why is wool considered biodegradable?
Wool is biodegradable because it is a natural protein polymer whose peptide bonds can be broken down by microorganisms and enzymes. Decomposition occurs through:
- Enzymatic hydrolysis of peptide bonds
- Conversion into amino acids
- Release of elements like carbon, nitrogen, and sulfur into the soil
9. What happens when wool is burned?
When wool burns, it decomposes slowly and produces the smell of burning hair due to its protein composition. Chemically:
- Keratin undergoes thermal decomposition
- Sulfur-containing amino acids release sulfur compounds
- A char residue rich in carbon remains
10. What is the difference between wool and synthetic fibers in chemistry?
The main chemical difference is that wool is a natural protein polymer, while synthetic fibers are usually petroleum-based polymers. For example:
- Wool: Protein (keratin) with peptide bonds
- Polyester: Synthetic polymer containing ester linkages such as in polyethylene terephthalate (PET)
