The Ultimate Guide to Wool Fiber: Benefits, Types and Uses

An Overview of  Wool Fiber

Protein Fiber:

Animal hair consists of complex proteins. The coat of sheep and goats is essential for textile. Wool is an animal fiber of outstanding importance. It comes from the fibrous covering of sheep, goats, camels, etc. 

For thousands of years, wool has been used for clothing and other textiles by different tribes and nations around the world. Till today wool fiber has great importance because of its unique natural properties that are absent in other natural and synthetic fibers.

Wool-producing countries:

The entire range of protein fibers accounts for only about 6% of world fiber consumption, whereas wool fiber contributes 90% of protein fiber consumption. The major wool-producing countries are- Argentina Australia, Britain, and England. Holland, Spain Germany, New Zealand South Africa, France, Canada, USA. Soviet Russia Pakistan, Iran, etc

Wool and Hair:

Wool and hair both are protein fiber that comes from the fibrous covering of sheep, goat, and camel Wool fibers have some special characteristics that are absent in hair Wool are short fine, curly, and elastic but hair are long coarse, less elastic, and no scale and stiffer than wool.

The Manufacturing Process of Wool:

Wool is a natural, multicellular; staple fiber that may be sheared from the living rural domesticated sheep or pulled from the hide Bar after the animal has been slaughtered for its sweet meet The sheep are sheared by early spring and the fleece is removed in one piece by expert shares, 

Sorting: Wool sorting is done by well-skilled workers who sort according to fineness; length and sometimes the strength of fibers. 

Scouring: It involves washing in warm soapy water several times to remove the natural grease of gum from the fiber and the saint dirt and dust.

Oiling: The wool fiber is treated with various oils including animal vegetables and minerals because unmanageable.

Gameting: The picking and shredding process of recycled and unused wool fiber is called garnering.

Carbonizing: After garnering, the wool fibers are put through a dilute solution of HCl or H₂SO, which destroys any vegetable fibers is called carbonizing. 

Felting of wool: When a fabric made from wool fibres is wet and is subjected to a suitable effective mechanical treatment of some sort such as rubbing: pressing and squeezing. Twisting or pounding. Wool felts because of their serrated surface structure or over-lapping epithelial cells but they are removed in one direction only to root ward due to less friction.

Morphological Structure of Wool: 

The morphological structure of wool fiber is extremely complex. The wool fiber exhibits wide variations in physical characteristics such as diameter and length. Its diameter can vary from 18-40 um along its length. The staple length of fibers removed from sheep varies greatly depending on a large number of factors such as the breed of sheep and the position of the fibers on the skins: From the morphological standpoint each individual wool fiber is divided into three sections. 

The root: It is the living part situated beneath the surface of the skin. 

The shaft/steam: It is cylindrical and tapers to a point at its free end. 

The tip: The free end of the fiber is naturally pointed. While the tip from the mature fleece is flat indicating that it has been. previously shown

In a typical Wool fiber, there are 10 district regions, which can be distinguished readily through the microscope.

a) The Outer Sheath or Epicuticles 

• This is the outermost layer and is a thin, water-repellent
• It is the only non-protein gait of the five and it protects the fibre like a covering of wak 
• The membrane repels water and in this sense acts as a waterproof coating on the fibre membrane.
• The epicuticle is, however, permitted by many microscopic pores, through which water vapor may penetrate into the interior of the fiber,

Fig: A Morphological Structure of wool fiber.

• Wool fabric will thus aber water vapor from the body Without feeling damp and will release it again slowly into the air
• The outer membrane is easily damaged by mechanical treatment. 

(b) The Scale-Cell Layer:

• Beneath the epicuticle layer of flat, scale-like cells that overlap like the shingles on a roof. 
• The free ends of the scales point towards the tip of the fiber.
• The epicuticle and scaly layer together form the cuticle of the fiber.

(c) The Cortex:

• Enclosed within the cuticle is the cortex which consists of millions of long spindle-shaped cells, thick in the center, and tapering to points at each end. 
• These cortical cells are 100-200 microns in length and 2-5 microns wide. 
• These cortical cells are themselves built up from fibrous components called fibrils. 
• These cells are found in lesser quantity in fine wool fibers (about 20 cells) than the coarser wools (about 50 cells) across the diameter of their cross-section.
• The cortex of wool fiber is composed of two distinct sections, namely Orthocortex and Para cortex', which differ from each other slightly in their physical and chemical characteristics.

(d) The Medulla

• A hollow space running lengthwise through the center of many wool fibers, especially the coarser fibers, is called the medulla.  
• The presence of the medulla contributes to thermal insulation and also increases the light-scattering properties of fibers. 
• It also causes some deterioration of fiber quality. These are 

1. -Medullated fiber suffers from Jower bundle strength.
2. -They cause lower spinning properties. 
3. -They produce lighter shade than the true wool fibers.

Chemical Composition of Wool:

Raw wool contains a variety of different chemicals and dirt that must be removed. These impurities may comprise as much as 60% of raw wool mass. They include wool wax, suits, and a range of vegetable and mineral debris.

Approximate composition of raw wool

Component                %

Wool keratin             33%

Wool-grease             28%

Suint                         12%

Water                         1%

Debris                       15%

Other Impurities       26%

The wool fiber is chiefly composed of a protein called keratin. The elemental composition of wool keratin is the same in different types of wool. Wool keratin contains the following elements:

Elements                    %

Carbon                      50

Oxygen                     22-25

Nitrogen                   16-17

Hydrogen                  7

Sulfur                        3-4

Chemical Structure of Wool: 

The wool fiber can be simply/described as a polypeptide, which is, produced through condensation of carboxyl and amino groups of 18 different amino acid residues as monomers having the general formula as given below:  R-CH-COOH

                               NH2

These amino acids are linked to each other using peptide bonds (-CO-NH-) to form the peptide chain.

wool fiber chemical structure

 The side groups of this chain may vary to a large extent in size and chemical nature. For instance, some of them may be hydrophobic, some hydrophilic, some acidic, or basic.

Different bonding in wool fiber:

The functional groups of wool polymer are -COOH, NH, -CONH 

1. Hydrogen bond(H-bond)

2. Salt linkage,

3. Cross-linkage and cystine linkage

4. Vander walls forces.

Polymer system in wool fiber:

The wool polymer is a linear keratin polymer with some very short side groups and it has a helical configuration. A wool polymer is about 140nm and about Inm thick, 25-30%crystalline. It has peptide bond(-CO-NI-H-bond, cystine linkages(disulphide bonds)

Classification of wool (by sheep):

Based on quality 

1. Merino Wool(Class-1):

• The merino, the most important of all the sheep used as a source of wool, produces fine and soft wool.
• Short staple length ranging from 1-5". 
• High scale per inch (about 118 per mm) and good felting properties.
• The merino sheep has been reared in Australia, South Africa and South America, New Zealand.

2. Class-2:

• Quality almost same to class-1 but length is a little bit higher (2-8)"
• Mainly produced in England, Scotland, and Ireland.

3. Class-3:

• Origin of this wool in the U.K.
• The length of this fiber is 4-8"
• Coarser, fewer scale and crimp, and less elasticity. 
• Mostly used in garment-making

4. Class-4:

• Mainly cross-bred wool
• The length of this fiber is 1-16"
• Coarser and hair-like. 
• Fewer scales and crimps and very little elasticity
• Used in carpet and blanket making.

Classification of wool by Fleece):

The fleece may be classified as a whole or, if vanable in qualify, separated into sections - such as shoulders, sides, back, thighs, and birth and belly. In general, the shoulders provide the best wool and the belly, tail, and legs give the poorest quality of wool.

Lamb's wool:

• The first fleece sheared from young sheep is known as lamb's wool.
• This wool is clipped at eight months.
• This wool is very fine and of excellent quality.
• Produced garments are soft and comfortable.
• Not too strong.

Hogget wool:

• Fleece is sheared from fourteen months old sheep that have not been previously shorn
• The wool is stronger, finer, and elastic. 
• Desirable wool and used as warp yarn
• Altogether, a sheep, on average, will provide between 0.9 to 4.54 kg of wool per year, according to breed. 

Whether Wool:

• Any fleece clipped after first shearing is called weather wool
• Wool is sheared from 14 or more years of wool
• Dusty wool.

Pulled wool: 

• When sheep are slaughtered for meat, their wool is pulled from the pelt by the use of chemicals (Lime or Sodium sulphide).
• Less quality wool due to the use of chemicals. 

Dead wool: 

• The wool has been recovered from the sheep that have died or have been accidentally died.
• Very low quality.
• Used in cheap garments. 

Cotty wool:

• Sheep that are exposed to severe weather conditions or lack of nourishment yield wool that is matted or felted. 

Taglocks:

• The torn, ragged, or discolored parts of a fleece are known as taglocks.

Considered points in wool:

The grading of wool fibers generally depends on their length fineness, luster, cleanness, color, and foreign matters. It depends on the experts who graded the wool by touching and seeing. Wool is graded in two systems-(1) the English system and (i) the American system.

All wool: When a fabric or garment is made from new fleece wool with a proportion of recovered wool. The garment is labeled 'all wool'.

Virgin wool: The garments or fabrics made from all wool are

interiors to those from new wools, so it is customary to refer to new wool materials as 'virgin wool'.

Recovered wool: When pure wool is mixed with used wool which has already been made into yarns and fabrics or worn to produce medium and low quality goods, the wool is called recovered wool. For insufficient production of pure wool, recovered wool is needed. The rags and waste fabric are used as raw materials for recovered wool.

Physical properties of Wool: 

• Length and fineness: Merino wool fibers are very fine (17-25 um) bill not very long (60-100mm) whereas Lincoln wool is coarser (around 40μm) in diameter but much on r. 75-250 mm). 
• Crimp: The crimp of wool fibers is most pronounced in the fine wool fibers The best merino wools, for example, will have 30 waves per inch. The elasticity of wool fiber is due to its crimp. Due to its crimp, wool yarns trap air and when used in garments, provide an insulating barrier to loss of body heat.
• Luster: Wool fibers have natural luster, which varies in its characteristics, Depending on the type of wool, Luster depends very largely on the nature of the fiber surface. 
• Tenacity: Wool has a tenacity of 8.8-15 cN/tex (1.0-1.7g/den) in a dry state and 7-14 cN/tex(0.8-1.6g/den) in the wet state. 
• Elongation: Wool has an elongation at a break of 25-35% under standard conditions and 25-50% when wet.
• Elastic property: Wool fibers are highly elastic and resilient. The elastic recovery of wool fibers is 65% for 20% extension and almost 100% for short extensions. 
• Specific gravity: Wool is a light-weight fiber with specific gravity of 1.32
• Effect of moisture and water: Wool fibers are hygroscopic and the most hydrophilic of textile fibers. Under ordinary atmospheric conditions, wool will hold 16-18% of its weight of moisture.

Chemical properties of Wool:

• Effect of acid: Wool is attacked by hot concentrated H.SO. and decomposes completely, It is in general resistant to other mineral acids of all strength, even at high temperatures, though nitric acid tends to cause damage by oxidation.
• Effect of alkalis: The chemical nature of wool keratin is such that it is particularly sensitive to alkaline substances, Wool will dissolve in caustic soda solutions that would have little effect on cotton fibers. Ammonium carbonate, borax, and sodium phosphate are mild alkalis that have minimum effect on wool.
• Effect of bleaching:
• Oxidizing agents: Oxidizing agents cause considerable change in the composition and properties of wool attacking preferentially in crystalline linkage. For bleaching purposes, hydrogen peroxide is commonly used as an oxidizing agent.
• Reducing agents: Wool is most strongly attacked by reducing agents in an alkaline solution they attack preferably on crystalline linkage. 
• Effect of Organic solvents: Wool has a good resistance to dry-cleaning and other common solvents.
• Insects: Wool is attacked by moth grubs and by other insects. 
• Microorganism: Wool has a poor resistance to mildew and bacteria and it is not advisable to leave wool for too long in a damp condition. 
• Dye ability: Easy to dye. Acidic mordant-nature in metalized, Reactive dye is suitable
• Effect of heat: Wool becomes weak and loses its softness en heated at the temperature of boiling water for long periods. At 130°C it decomposes and turns yellow, and it chars at 300C As it decomposes, wool gives off a characteristic smell, similar to that from burning feathers. 
• Wool does not continue to burn when it is removed from a flame
• The action of sunlight: The keratin of wool decomposes under the action of sunlight, a process that begins before the wool has been removed from the shsulfure sulphur in wool is converted into sulphuric acid; the fiberdiscoloredscoloured and develops a harsh losesIt losses strength and the dyeing properties are affected.

Felting properties of wool:

• The tendency of wool to feel is a distinctive property that is not found in many other textile fibers. The scaly layer of wool fiber is responsible for this property.
• Washing of woolen articles causes irreversible shrinkage and felting 
• Mechanical compression and relaxation of the fibers in a woolen fabric during washing allow the edges of wool fibers to migrate only in the direction of the root end. The migrated fibers,theiring to its scale structure are interlocked with each other preventing the fiber from returning to its original position. This irreversible shrinkage is called felting. 
• It closes up the fabric structure, making it much more compact and has increased rigidity.

Shearing of wool:

Sheep are normally shorn of their fleece every year (in some countries, e.g. g. South Africa, up to twice a year).

• On large-scale production, power-operated clippers remove the fleece. 
• Inefficient hands, the sheep is parted from its wool in two and a half mfirst-classirst class sheerer can shear two hundred sheep in a day, from which he will clip a tonne or more wool. This type of wool is known as Fleece or clip wool."

Immediately after it has been removed, the fleece is "skirted". This involves pulling away the soiled wool around the edges. Then the whole fleeces are graded by experts who judge the fineness, le,ngth r and the other characteristics. Finally, the various grades are packed into large sacks and then sewn up into the bales. Each bale contains about 136 kg (300 lb) or more of woolThe settinging of wool:

Wool and other animal fibers can be formed into a desired shape and then persuaded to retain that shape for some time. More permanent forms of setting have been used in the textile industry for a long time, usually involving the simultaneous use d water and heat. Three well-known processes of this sort are

(i)Crabbing 

(ii)Blowing and 

(iii)potting. 

There are different degrees of setting of wool athe nd set is graded empirically into three degrees; cohesive, tempor,ary and permanent

DFE: 

The felting friction is fiber the fibre moves in a rootward direction upward a upward direction. The difference of surface friction between two direction is called directional friction effect. (DFE)

DFE of Wool

Fig: A simplified representation of the wool felting.

Carbonizing:

Burrs, twings, and other vegetable material can be destroyed by steeping the wool in dilute HSO, and then heating at high temperature. The cellulosic material is charred and can then be broken up and beaten out of the wool. This process is called Carbonizing.

Woolen and worsted yarns:

Woolen yarns: Woolen yarns are thick and full; the fibers are held loosely and subjected to only a limited twist during spinning. These yarns, made usushort-stapleort staple wool, are woven into thick, full-bodied materials such as tweeds or blankets and used for knitting. Often, woolen yarns are spun from a mixture of new wool with reclaimed wool, or with ray,on, cotton or other fibers

Worsted yarns: Worsted yarns are finer, smooth,r and firmer than woolen yarns. In worsted yarn, the fibers are lying more parallel and are more tightly twisted, producing a thinner yarn witha 

smoother surface. Worsted yarns are spun commonly from fibers 5- 38 cm (2-15 inch) long. These yarns are woven into fine dress materials andsuitsg. Worsted spun yarns with less twist are used for knit fabrics.

Difference between woolen and worsted yarn:

Woolen yarn            Worsted yarn

Short staple fiber     long staple fiber

Only carded             Carded and combed

Coarser yarn            Finer

Slightly twisted       Higher twisted

Softer                      Harder

Weaker                   Stronger

End uses of wool:

One of the first things we meet on entering the world is wool. Woolies are worn by babies because they are warm and airy, Wool cloths are healthy and hard wearing.

Due to crimp, each fiber stands away from its neighbours. Air is trapped in the spaces between the fibers, creating an insulating layer, which is responsible for wool's warmth as a material. Used in suiting, and dréss materials, blankets, carpets, jackets.