Wool fiber – Basics, Characteristics, & Properties

Of the major apparel fibres, wool is the most reusable and recyclable fibre on the planet. The eco-credentials of wool are enhanced by its long service life and suitability to be recycled to new textiles for clothing, resilient upholstery or products that call on its natural resistance to fire and temperature extremes. Aside from premium next-to-skin apparel, wool can be used in industrial applications such as thermal and acoustic insulation or in pads to soak up oil spills.

At the disposal stage, natural fibres such as wool reduce the impact of the textile industry on pollution and landfill build-up. In warm, moist conditions such as in soil, wool biodegrades rapidly through the action of fungi and bacteria to essential elements (i.e. Nitrogen and Sulphur) for the growth of organisms as part of natural carbon and nutrient cycles.

Growth

Wool is possibly the oldest fibre known to humans. It was one of the first fibres to be spun into yarn and woven into a fabric. Wool mostly comes from sheep but also from alpacas, camels, and goats. Australia, Eastern Europe, New Zealand, and China are major wool producers. The American woollen industry began in the Massachusetts settlements in 1630, where each household was required by law to produce wool cloth.

How is wool made?

First, our sheep needs to grow it!

Harvesting

 

Then, they need a haircut. The process is called sheering. A sheering specialist can sheer 200 sheep in a day. A ewe, or female sheep, can produce up to 15 pounds of wool. A ram, or male sheep, can 20 pounds of wool. The sheared wool is called raw wool and since sheep don’t take showers, it must first be cleaned.

Next, the wool is carded – that means brushing the wool to straighten the fibres. Once done by hand, these days a carding machine passes the wool through a series of rollers covered with wire bristles. The carded fibres are gently scraped into strands called roving. The roving is spun into yarn that is then woven into cloth. In the past, the task of spinning usually was the job of unmarried females – they became spinsters.

Fleece is a ball of wool taken from a single animal in a shearing. But not all wool is equal – even when it comes from the same animal. The highest quality wool comes from the sides, shoulders, and back. The lowest quality comes from the lower legs.

Grading of Wool Fibers

Wool is graded for fineness and length. The length varies from place to place on the animal, but it mostly varies amongst sheep breeds. Australian Merino wool is 3-5 inches long. Breeds found in Texas and California produce fibres 2.5 inches long. Wool from other breeds and other animals may be as long as 15 inches.

Properties of Wool Fibers

This microscopic view shows us why wool is special. The surface is a series of overlapping scales of protein, pointing toward the tip. On the animal, this enables the foreign matter to work its way out of the fleece. In a strand of yarn, it enables the fibres to lock with one another. This is the key to wool’s strength.

Wool’s surface repels water. Since moisture does not remain on the surface, woollen fabrics tend to feel dry and comfortable even in damp weather. The inner core does absorb moisture – so much so that wool can absorb almost double its own weight in water and still feel reasonably dry. This absorbency also gives wool its natural resistance to wrinkles. The absorbed moisture also holds down static electricity. And because of the inner moisture, wool is naturally flame resistant.

Moisture in wool

The amount of water absorbed by wool is usually referred to as ‘regain’. Regain is the ratio of the mass of water to dry wool expressed as a percentage.

Another term also used by the textile industry, predominately for cotton, is ‘moisture content’. Moisture content is the ratio of the mass of water to the mass of water plus wool expressed as a percentage.

Wool, along with cotton and to lesser extent nylon, is a fibre that absorbs moisture from the surrounding air to reach an equilibrium, which depends on the relative humidity of the environment. At ambient humidity, wool will contain 10 to 15% by weight of water and up to 35% water at high relative humidity, which is more than most other fibres. This water is incorporated in the internal structure of the fibre and, therefore, is hardly noticed by the wearer. Wool garments do not feel damp or clammy. This property enables wool to act as a buffer against sudden environmental changes, for example, excessive perspiration during exercise or changes in climatic conditions such as going outside from an air-conditioned room.

Although the wool fibre can readily absorb water vapour from the air, a garment made from wool will be water repellent to some extent. This is because the surface of the fibre has a very thin, waxy, lipid coating chemically bonded to the surface that cannot be easily removed. Scouring, washing or processing will not remove this layer. The only way to
remove this layer, if required, is by chemical treatment.

Shrinkage and felting

 

There are two major sources of shrinkage in wool-containing fabrics, which may be encountered during laundering: relaxation and felting shrinkage.

Relaxation shrinkage is an irreversible change in fabric dimensions (expansion or shrinkage) that occurs only once when a fabric is first immersed in water (without agitation) and then allowed to dry. Relaxation shrinkage is caused by the release of temporarily set strains imposed on the fabric in dry finishing and can be minimised by suitable finishing routes.

Felting shrinkage is a form of shrinkage unique to wool and wool-rich fabrics and is caused by the scales on the surface of wool fibres that have a ratchet-like action allowing preferential movement of the fibre in the direction of the fibre root. This results in the entanglement of the fibres as they move under mechanical action in water (as occurs in
machine washing).

Physical properties

• Crimps: Wool fibre is more or less wavy and has twisted. This waviness is termed as ‘crimp’. The finer the wool the more will be the crimps in it. Merino wool has 30 crimps per inch while coarse wool has one or two.
• Effect of friction: Friction will soften the wool fibre especially when wet and thus is advantageous in maintaining the smooth, soft texture of fabrics.
• Effect of heat: Low heat has no effect but strong heat weakens the fibre and destroys the colour of the fibre.
• Effect of moisture: Wool is the most hygroscopic in nature. It can absorb up to 50% of its weight and carry up to 20% of weight, without giving the feeling of being wet. Upon drying it losses moisture slowly preventing rapid evaporation thus avoiding a chilling feel to the user. It absorbs perspiration after violent exercise and guards the body against the sudden change in temperature.
• Felting: Wool fibres interlock and contract when exposed to heat, moisture, and pressure. The scale-like exterior of the fibres contributes to felting. The fibres get softened in weak alkaline solutions due to the expansion of scales at their free edges, with friction and pressure they again interlock to form a felt. This property is used in making felts for hats, shoes, floor-coverings and soundproofing purposes.
• Heat conductivity: Wool fibre is a part that is a poor conductor of heat and therefore the fabrics made from the fibre are considered most suitable for winter wear.
• Resiliency: Wool is highly resilient and comes to its original shape when hanged after wrinkled or created.
• Strength: It is stronger than silk. When wet wool loses about 25% of its strength. The longer the fibre the greater will be the strength of the yarn.
• Stretchability: Wool is highly elastic. It is about 10 to 30% stretched when dry and 40 to 50% when wet upon receiving pressure upon drying it readily regains its original dimensions.
• Shrink-ability: Wool is resistant to shrinkage. However long exposure to moisture may cause shrinkage.

Chemical properties

Wool is resistant to acid, whereas cotton and cellulose are severely damaged if exposed to acid. This difference is utilised in carbonising wool to remove excessive cellulosic impurities, such as burr and vegetable matter. Wool is treated with a solution of sulfuric acid and is then baked to destroy the impurities with only minimal damage to the wool.

The differences in the chemical structure of the various fibres mean that different classes of dyestuffs are required to cover the range of fibre types. Polypropylene and polyethene do not absorb the dyes used to colour wool so any wool pack contamination from these fibres in the final product will appear obvious. The move to nylon woolpacks does not
necessarily prevent contamination; however, as the chemical structure of nylon is similar to wool, it absorbs wool dyes and this makes any contamination less obvious.

• The action of acids: Dilute acids have little effect but either hot or concentrated acids weaken or dissolve the wool fibres.
• The action of alkalis: Alkalis tend to make wool yellowish, strong solutions of sodium carbonate when heated destroys the fibre sodium hydroxide is highly injurious to the wool fibre. However borax and ammonia have no harmful influence on wool.

Application of Wool Fibers

Wool today is prized for its beauty and durability. It is still the prime choice for high-quality business suits, warm sweaters, and premium carpets.

The majority of wool (72.8%) is used in apparel, home furnishing account for 15-45%, industrial uses 6 to 7% and exports 5%, wool accounts for 3.3% of all fibres for apparel.

The most important use of wool is for apparel coats, jackets, suits, dresses, skirts, slacks made from woven fabrics of varying weights and knitted fabrics’.

In the home furnishing area, the major use of wool is in carpets and rugs where wool is used more, cover to the carpets and warm in the rugs. Blends of different synthetic fibres with wool for suiting materials are increasingly important.
This result in fabrics that are more appropriate in warmer conditions. Polyester is the most important fibre used in blending with wool.

Characteristics of Wool Fibers and Products

• Anti-static — because wool can absorb moisture vapour, it tends not to create static electricity, so it is less likely to cling uncomfortably to your body than other fabrics.
• Anti-wrinkle — at a microscopic level, each wool fibre is like a coiled spring that returns to its natural shape after being bent. This gives wool garments natural wrinkle resistance.
• Biodegradable — When wool is disposed of, it will naturally decompose in soil in a matter of months to years, releasing valuable nutrients back into the earth.
• Biodegradable — When wool is disposed of, it will naturally decompose in soil in a matter of months to years, releasing valuable nutrients back into the earth.
• Breathable — wool fibres can absorb large quantities of moisture vapour then move it away to evaporate into the air. Wool clothing is extremely breathable and less prone to clamminess.
• Elastic — natural elasticity helps wool garments stretch with your body, yet return to their original shape. So fine wool clothing is ideal to wear when exercising.
• Fire-resistant — wool is flame retardant, doesn’t melt and stick to the skin, and even self-extinguishes when the source of flame is removed.
• Nature’s fibre — Wool is grown year-round from a simple blend of water, air, sunshine and grass.
• Odour resistant — in contrast to synthetics,  wool can absorb moisture vapour, which means less sweat on your body. They even absorb and locks away the odours from sweat, which are then released during washing.
• Renewable — every year sheep produce a new fleece, making wool a completely renewable fibre source
• Stain-resistant — wool fibres have a natural protective outer layer that prevents stains from being absorbed. And because wool tends not to generate static, it attracts less dust and lint.
• Soft — Wool fibres are extremely fine, enabling them to bend and feel soft and gentle next to your skin.
• Sun-safe — wool is much better at protecting skin against UV radiation than most synthetics and cotton. So the whole family will be safer wearing wool on sunny days.
• Sun-safe — wool is much better at protecting skin against UV radiation than most synthetics and cotton. So the whole family will be safer wearing wool on sunny days.
• Warm and cool — in contrast to synthetics, wool is an active fibre that reacts to changes in body temperature. So it helps you stay warm when the weather is cold, and cool when the weather is hot.

Summary of Characteristics of Wool Fibers

• Wool is a protein fibre that comes from a variety of animals.
• Sheering is done by hand, but the manufacturing of wool fabric is done by machine.
• Wool is ideal for cool weather garments such as sweaters.
• Flame resistant (wool usually extinguishes itself when the source of flame is removed)
• Weaker than cotton or linen, especially when wet
• Fibres range from one to fourteen inches long
• Most valued for its textured appearance and warmth
• Must be washed gently or dry cleaned
• Can be damaged by chlorine bleach
• Moths and carpet beetles eat wool
• Springs back into shape after being crushed
• An excellent insulator as woollens (80% air)
• Absorbs moisture which is held inside the fibre (the wool will still feel dry even on a humid day)
• Accepts dyes easily (“dyed in the wool”)
• The quality of wool varies with the breed of sheep
• Does not attract dirt or static electricity
• The wool products labelling Act permits the word “wool” to be used for fibres from sheep, Angora or Cashmere goats, camel, alpaca, llama, and vicuna.