WOOL

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WOOL FIBRE
Wool is the natural textile fiber obtained from sheep and other animals, including
Cashmere from goats
Mohair from goats
Qiviut from muskoxen
Angora from rabbits
And other types of wool from camelids.
Wool has several qualities that distinguish it from hair or fur: it is crimped, it is elastic, and it grows in staples.
CHARACTERISTICS OF WOOL :

Wool is composed of the protein substance called as (keratin). Wool is composed of carbon, hydrogen, nitrogen and this is the only animal fiber, which contains sulphur in addition. The wool fibers have crimps or curls, which create pockets and give the wool a spongy feel and create insulation for the wearer. The outside surface of the fiber consists of a series of serrated scales, which overlap each other much like the scales of a fish. Wool is the only fiber with such serration’s which make it possible for the fibers to cling together and produce felt. 

Wool is produced by follicles which are small cells located in the skin. These follicles are located in the upper layer of the skin called the epidermis and push down into the second skin layer called the dermis as the wool fibers grow. Follicles can be classed as either primary or secondary follicles.  Primary follicles produce three types of fiber, Kemp (wool), modulated fibers and true wool fibers.  Secondary follicles only produce true wool fibers. Modulated fibres share similar characteristics to hair and are long but lack crimp and elasticity. Kemp fibers are very coarse and shed out. Wool’s scaling and crimp make it easier to spin the fleece by helping the individual fibers attach to each other, so they stay together. Because of the crimp, wool fabrics have greater bulk than other textiles, and they hold air, which causes the fabric to retain heat. Wool has a high specific heat coefficient, so it impedes heat transfer in general. This effect has benefited desert peoples, as Bedouins and Tuaregs use wool clothes for insulation. Felting of wool occurs upon hammering or other mechanical agitations as the microscopic barbs on the surface of wool fibers hook together. The amount of crimp corresponds to the fineness of the wool fibers. A fine wool like Merino may have up to 100 crimps per inch, while coarser wool like karakul may have as few as one or two. In contrast, hair has little if any scale and no crimp, and little ability to bind into yarn. On sheep, the hair part of the fleece is called kemp. The relative amounts of kemp to wool vary from breed to breed and make some fleeces more desirable for spinning, felting, or carding into batts for quilts or other insulating products, including the famous tweed cloth of Scotland. Wool fibers readily absorb moisture but are not hollow. Wool can absorb almost one-third of its own weight in water. Wool absorbs sound like many other fabrics. It is generally a creamy white color, although some breeds of sheep produce natural colors, such as black, brown, silver, and random mixes. Wool ignites at a higher temperature than cotton and some synthetic fibers. It has a lower rate of flame spread, a lower rate of heat release, a lower heat of combustion, and does not melt or drip; it forms a char which is insulating and self-extinguishing, and it contributes less to toxic gases and smoke than other flooring products when used in carpets. Wool carpets are specified for high safety environments, such as trains and aircraft. Wool is usually specified for garments for firefighters, soldiers, and others in occupations where they are exposed to the likelihood of fire.[6] Wool is considered by the medical profession to be allergenic

PROPERTIES OF WOOL FIBRE
the characteristics of Wool fiber or protein fibers are as follows:

  1. They are composed of amino acids.
  2. They have excellent absorbency.
  3. Moisture regain is high.
  4. They tend to be warmer than others.
  5. They have poor resistance to alkalis but good resistance to acids.
  6. They have good elasticity and resiliency.
CHEMICAL COMPOSITION OF WOOL FIBER:
Kartain 33%
Dust 26%
Suint 28%
Fat 12%
Mineral Water 1%
DIFFERENT TYPES OF WOOL :
  1. Fine Wool
  2. Medium Wool.
  3. Long breeds wool
  4. Crossbreeds wool
  5. Carpet wool

CLASSIFICATION OF WOOL

the quality of wool fibers produced is based on the breeding conditions, the weather, food, general care etc. For example, excessive moisture dries out natural grease. Similarly, the cold weather produces harder and heavier fibers. The wool could be classified in two different ways:

  1. Classification of wool by sheep:
  2. Classification of Wool By flees :
  1. Classification of wool by sheep:

The wool is classified according to the sheep from which it is sheared as given below

a. Merino Wool (First Class Wool): Merino sheep originated in Spain yields the best quality wool

  • These fibers are strong, fine and elastic fiber which is relatively short, ranging from 1 to 5 inches (25 – 125 mm).
  • Among the different wool fibers, merino wool has the greatest amount of crimp and has the maximum number of scales. These two factors contribute to its superior warmth and spinning qualities.
  • Merino is used for the best types of wool clothing.

b. Class two wool: This class of sheep originates from England, Scotland, Ireland and Wales.

  • The fibers are comparatively strong, fine, and elastic and range from 2 to 8 inches (50 – 200mm) in length.
  • They have a large number of scales per inch and have the good crimp.

c. Class three wool: This class of sheep originates from the United Kingdom.

  • The fibers are coarser and have fewer scales and less crimp when compared to earlier varieties of wool fibers and are about 4 to 18 inches long.
  • They are smoother and are more lustrous.
  • These wool are less elastic and resilient.
  • They are of good quality, used for clothing.

d. Class four wool: This class is a group of mongrel sheep sometimes referred to as half-breeds.

  • The fibers are about 1 to 16 inches (25 – 400 mm) long, are coarse and hair like, and have relatively few scales and little crimp.
  • The fibers are smoother and more lustrous.
  • This wool is less desirable, with the least elasticity and strength. It is used mainly for carpets, rugs, and inexpensive low-grade clothing.
  1. Classification of wool by fleece: Shearing is the process by which the woolen fleece of a sheep is removed. Sheep are generally shorn of their fleeces in the spring, but the time of shearing varies in different parts of the world. Sheep are not washed before shearing. They are sometimes dipped into an antiseptic bath as prescribed by law. The classification by fleece is as follows:
    1. Normal (Lamb’s) wool.——– ( 6 to 8 years of sheep )
    2. Haggett wool ———————( 12 to 14 years of sheep)
    3. Pulled wool ———————-( 15-16 years of sheep)
    4. Cotty wool ———————–( very low-quality sheep)
    5. Taglock wool ——————-( Discolor sheep )
    6. Dead wool ———————– ( Nearly dead sheep)
    7. Weather wool ——————-( Collecting after one collection)
      1.  Lamb’s Wool: The fleece obtained by shearing the lamb of 6 to 8 years old for the first time is known as lamb’s wool. It is also referred to as fleece wool or first clip. As the fiber has not been cut, it has a natural, tapered end that gives it a softer feel.
      2. Hogget Wool: Hogget wool is the one obtained from sheep about 12 to 14 years old that have not been previously shown. The fiber is fine, soft, resilient, and mature, and has tapered ends. These are primarily used for warp yarns.
      3. Pulled Wool: Pulled wool is taken from animals originally slaughtered for meat. The wool is pulled from the pelt of the slaughtered sheep using various chemicals. The fibers of pulled wool are of low quality and produce a low-grade cloth.
      4. Cotty Wool: This type of wool is obtained from the sheep that are exposed to severe weather. As discussed; the severe weather conditions hamper the qualities of the fleece obtained. The cotton wool is of a poor grade and is hard and brittle.
      5. Taglocks: The torn, ragged, or discolored parts of a fleece are known as tag locks. These are usually sold separately as an inferior grade of wool.
      6. Dead Wool: This is the wool obtained from the sheep that have died of age or accidentally killed. This type of wool fiber known should not be confused for pulled wool. Dead wool fiber is decidedly inferior in grade; it is used in low-grade cloth.
      7. Weather Wool: Weather wool is the one obtained from the sheep older than fourteen months. The shearing is not done for the first time and in fact, these fleeces are obtained after the first shearing. These fleeces contain much soil and dirt.
        Processing of Wool :
        Wool processing involves many operations, both dry and wet processes. The processes carried out in a woolen mill
  2. Fibre Shearing and Grading;
  3. Fibre Preparation
  4. Washing and Scouring
  5. Blending
  6. Stock Dying
  7. Oiling
  8. Weaving Operation
    a. Carding
    b. Spinning c. Weaving / Knitting
    d. Finishing
    e. Fulling
    f. Wool Carbonising
    g. Piece Dying
    h. Bleaching
  1. Fibre Shearing and Grading: In this first stage of wool processing, fiber is collected from the body of the animals through Shearing and then their suitability for processing is determined through Grading.
    1. Sheep shearing is the process by which the woolen fleece of a sheep is cut off. After shearing, the wool is separated into four main categories: fleece (which makes up the vast bulk), broken, bellies, and locks. The quality of fleeces is determined by a technique known as wool classing, whereby a qualified person called a wool classer groups wools of similar gradings together to maximize the return for the farmer or sheep owner. In Australia before being auctioned, all Merino fleece wool is objectively measured for micron, yield (including the amount of vegetable matter), staple length, staple strength, and sometimes color and comfort factor. The sheep is given a dip in antiseptic solution after shearing, so as to cure the wounds caused during shearing.
      1. Grading: Grading is done for establishing the quality of raw fiber with respect to fiber length, diameter, amounts of dirt, and other impurities. These factors are determined either by the experienced Graders or by the prospective buyers themselves who take the samples for the purpose. Graders can do the job simply through visual inspection. Fine and medium-fine wools having longer staple lengths of more than three inches are considered to be of good quality and are used for making a light-weight worsted suit and dress fabrics. Coarser and short staples of less than three inches long are used for making bulky sweater and carpet yarns.
      2. Fibre Preparation: Fibre Preparation 60% of the raw wool fiber is composed of impurities and only 40% of it is usable wool fiber. The impurities present in wool are of three types- natural; acquired; and applied impurities. Natural impurities are the glandular secretions that adhere to the fleece. Suite and wool grease, together known as yolk, are such two major components. A suite is the dried perspiration of sheep that is water soluble. Wool grease is water-insoluble and requires special scouring for its removal. The acquired impurities include soil, dust, dirt, straw, vegetable and fecal matter. Applied impurities are due to the treatments are given to the animal against insects, pests etc. and due to the markings made on them with tar or paints for their identification.
      3. Washing and Scouring: The water soluble suint and other heavy dirt particles are removed by washing the raw wool with water at a temperature of 32°C to 42°C. The water-insoluble wool grease is removed by treating the disunited wool with a mixture of detergent and sodium sulphate (or chloride) at the temperature of 65°C. As the detergent scouring yields waste of very high strength, some mills prefer to remove the impurities by solvent scouring wherein the disunited wool is scoured with organic solvents such as benzene, carbon tetrachloride, ethyl alcohol, methyl alcohol or isopropyl alcohol. Although solvent scoring removes grease effectively, dirt is not removed. Thus, solvent scouring is generally followed by a detergent wash.After scouring, the woollen fibres are rinsed with water at a temperature of 46°C to 50°C to remove the residual chemicals and remaining dirt.
      4. Blending: Clean wool fibres from several different batches are often blended or mixed mechanically. Blending helps in unifying the slightly-different basic colors of raw wool, and also standardizes staple length and diameter for uniform quality
      5. Stock Dyeing: Wool fibres absorb dyes very efficiently at any processing stage. Wool dyed immediately after scouring is called to be a stock-dyed fibre. It is dyed either in open or pressure type machines, after which the dyed fibre is rinsed thoroughly with water. The various types of dyes used for woollen dyeing are direct dyes, acid chrome, metachrome, pure mordant dyes and premetallized acid dyes. Vat dyes are also used under special circumstances.
      6. Oiling: The cohesion of fibres are increased by oiling, which also helps in spinning. Olive oil or a mixture of lard and mineral oil is used for the purpose. The quantity of oil used varies from 1 to 11% of the wool’s weight. The applied oil is washed out during finishing operations.
      7. Weaving Operations:  After the dry operations, the wool fibre is woven into woollen fabric.
        1. Carding: The clean and dry wool is passed through wire rollers to straighten the fibres and remove any remaining impurities. Carding results in a thin web of aligned fibres. Smooth steel fingers are then used to divide the web and roll the strands over onto one another which create narrow continuous ropes of fibres known as “slivers”. If the treated batch of wool is of coarser fibre and shorter staple length the machine gently twists the slivers into ropelike strands called “roving“, and winds the roving into balls ready for spinning into woollenyarns that are used for making bulky sweaters and carpets. If the batch consists of finer fibre and longer staples then the slivers usually go through the combing and drawing steps which prepare them for spinning into worsted yarns that are used for making suits, dresses, and gabardines.
        2. Spinning: Roving prepared for both woolen and worsted yarns go through the spinning process for yarn formation. After spools of roving are mounted on the spinning frame, the ends of the roving are drawn through small rollers to extend the wool fibers still further. Then the spinning machines give repeated twists to the roving thus converting them into yarns having different properties of varying strength, firmness, size and ply.
        3. Weaving and Knitting: In weaving, two distinct sets of yarns called the warp and the weft is interlaced at right angles with each other to form a woven fabric. Knitted fabrics are produced by interlocking rows of yarns and loops. As new loops are formed, they are drawn through those previously formed. A circular knitting machine primarily manufactures jersey and a variety of double knits. Flat knitting machines make yard goods like tricot and raschel knits.
        4. Finishing Operations: A thorough examination of the produced cloth brings out the imperfections such as broken threads, variations in color and other undesired effects. These are removed and the area is rewoven by hand if necessary. The fabric then undergoes certain wet processes to acquire the required finish and for the removal of any traces of impurities.
        5. Fulling: This wet process is adopted for giving a controlled shrinkage to the woven cloth. It converts even a loosely woven cloth into a tight, closely woven woolen fabric. It improves the texture of the fabric which feels like a felted cloth. Both the types, acid fulling, and alkali fulling are adopted by the wool mills. In acid fulling, dilute solution of sulfuric acid and hydrogen peroxide are used along with small quantities of metallic catalysts. It is usually carried out for heavy fabrics such as blankets, military uniforms, felt cloth etc. In alkali fulling, soap or detergent, sodium carbonate, and a sequestering agent are used. It is meant for delicate woolen garments. After fulling, the fabric is washed extensively twice or thrice in order to remove the excessive chemicals.
        6. Wool Carbonizing: It is the final process applied for removing burrs and other impurities remaining in the wool. The woolen fabric, impregnated with the sulfuric acid solution, is oven dried at 100°C to 104°C followed by mechanical agitation. The acid degrades the cellulosic impurities without harming the wool. During drying, the sulfuric acid becomes more concentrated due to water evaporation resulting in the burning of remaining impurities. The fabric is then passed through pressure rollers to crush the solid carbon residue. The loosened carbon residue is removed from the wool by passing it through the mechanical agitators called dusters. The fabric is then rinsed with water, passed through baths containing sodium carbonate solution to neutralize the residual acid, washed again and then dried.
        7. Piece Dyeing: If the wool had not died at the fiber stage then it is dyed following the piece dyed method after carbonizing.
        8. Bleaching or Brightening: At times, mild bleaching is also done with sulphur dioxide or hydrogen peroxide to whiten the natural yellow tint of the wool.

BENEFITS

  • Resists wrinkles
  • Wool springs back quickly
  • Resists soiling
  • Because the fiber is complex
  • Is durable
  • Multi-part fiber resists wear
  • Repels moisture
  • Fiber sheds water
  • Retains shape
  • Resilient fibers return to the size
  • Resists flames
  • Fibers will not support combustion
  • Is comfortable in all seasons
  • Keep a layer of air next to skin

DURABILITY AND RESILIENCE Each wool fiber is a molecular coil spring making the fiber remarkably elastic. Nature has folded the chemical polypeptide chains back upon themselves in such a way that they act like a coiled spring which elongates when it is extended and retracts when it is released. This molecular crimp, along with the 3-dimensional fiber, allows wool fibers to be stretched up to 50% when wet and 30% when dry and still bounce back to their original shape when stress is released. But be careful: When wool is wet the fibers are weaker. Recovery from stress takes place faster when the fiber is in a humid environment; that’s why steaming a wool garment will freshen the fabric and why a steam iron is recommended for pressing wool. The flexibility of the wool fiber also makes it more durable. A wool fiber can be bent back on itself more than 20,000 times without breaking, compared to about 3,000 times for cotton and 2,000 times for silk. The natural elasticity of wool also makes woolen fabrics resistant to tearing. In addition, the outer skin of the wool fiber acts as a protective film, giving wool cloth improved resistance to abrasion.

FIBER ABSORBENCY Wool is a hygroscopic fiber; it takes up moisture in vapour form. Tiny pores in the epicuticle make the fiber semi-permeable, allowing vapour to pass through to the heart of the fiber. Wool can easily absorb up to 30% of its weight in moisture without feeling damp or clammy. The capacity to absorb makes wool a “temperature regulator” because it can protect the body in both cold and warm conditions. Wool always absorbs moisture from the atmosphere of greater humidity and releases it to the drier environment as it creates a balance in moisture conditions. This characteristic makes wool a versatile all-season fabric. Wool absorbs perspiration; thus it keeps a layer of dry air next to the skin which, in turn, helps to hold in body heat. As wool absorbs atmospheric moisture, the hydrogen bond of water is broken and chemically reacts with molecules of the wool to generate heat. Wool garments are therefore regarded as the good protection against hypothermia… a condition that occurs when a sudden drastic lowering of body temperature causes the body to lose heat faster than it can be produced. The same principle of moisture contact on the skin acts to protect against hot weather as well. The body cools itself naturally with the evaporation of perspiration. Wool expedites this process by absorbing perspiration and keeping the same dry air next to the skin. This is why wool clothing is worn throughout the desert regions of the world where it’s hot during the day and cool at night.

FELTS NATURALLY The physical structure of the outer scaly layer of the wool fiber contributes to wool’s unique property of felting. Under the mechanical action of agitation, friction and pressure in the presence of heat and moisture, the scales on the edges of the wool fibers interlock, preventing the fiber from returning to its original position. Felting shrinkage is irreversible. The felting property of wool is both an advantage and disadvantage. In a controlled situation, the felting quality is called fulling or milling and creates a softer finish for woven wool fabric. Felting is also an advantage because it provides for a wide variety of non-woven felt fabrics for hats and for industrial uses. Felting is a disadvantage because it makes the washing of untreated wool fabrics difficult. Treatments have been developed to prevent felting shrinkage, allowing wool garments to be machine-washed. The SUPERWASH mark certifies that fabrics have been treated for machine-washability and dry-ability under strict standards set by The Wool Bureau, Inc. Technically, the process involves a mild chemical treatment applied to the fiber to form a microscopic film of resin that spreads evenly over the fiber surface. The film reduces friction and thus eliminates entanglement. The resin can’t be washed or worn off; it is held in place permanently by chemical adhesive bonds.
TAKES DYE BEAUTIFULLY Wool absorbs many different dyes deeply, uniformly and directly without the use of combining chemicals. Wool is amphoteric, which means it reacts with both acids and bases; thus it accepts both acid and basic dyestuffs. Dyes penetrate into the inner medulla core of the fiber where a chemical reaction occurs making the color change permanent except under extreme and prolonged fading conditions. RESISTANCE TO
FLAME Because wool contains moisture in each fiber, it resists flame without chemical treatment. Instead of burning freely when touched by flame, wool chars and stops burning when it is removed from the source of the fire. Wool is self-extinguishing. It will not support combustion; this is why wool blankets are recommended for use in extinguishing small fires.
CHEMICAL STRUCTURE Wool is a natural protein fiber that grows from the follicles of the sheep’s skin. It is like human hair in that it is composed of keratin-type protein. Chemically these proteins contain 5 elements: carbon, hydrogen, oxygen, nitrogen, and sulphur. These 5 elements are combined into 19 amino acids linked together in ladder-like polypeptide chains.
RESISTANCE TO COMPRESSION 
Resistance-to-compression values are useful in assessing the suitability of wool for specific end uses. Resistance to compression (R to C) is the force per unit area required to compress a fixed mass of wool to a fixed volume. Resistance to compression is related to fiber diameter and the form and frequency of crimp. For instance, low and medium R to C wools tend to be softer, more lustrous, more susceptible to felting, easier to process and produce strong fabrics. On the other hand, high R to C wools have a harsher handle, are resistant to felting and are bulkier. Two resistance-to-compression studies conducted by Texas A&M University prove American wool is well-suited to produce the finest of fabrics as well as wool batting for the production of futons and other bedding materials. These studies confirmed that there is a good variety of wools available in the U.S. with low, medium and high resistance to compression. The majority of the wool finer than 28 microns in this test was analyzed as being in the middle resistance-to compression range (53%). On the other hand, some 73 percent of the wool coarser than 28 microns was evaluated to be highly resistant to compression.
Tenacity: 
Wool is a complicated weak fiber. The low tensile strength is because of comparatively fewer hydrogen bonds. When it absorbs moisture, the water molecules steadily force sufficient polymers apart to cause a significant number of hydrogen bonds to break. The water molecules also hydrolyze several salt linkages in the amorphous regions of the strand. Breakage and hydrolysis of these inter-polymer forces of attraction are explicit as swelling of the fiber and result in loss of strength of the wet woolen material.
Elasticity and resiliency: 
This is elastic and resilient. Covalent bonds can stretch, but they are strong. The disulfide bonds in the amorphous parts of the strand or fiber are able to stretch when the strand is extended. When the strand is released the disulfide bonds pull the protein molecules back into their original positions. If there are too few disulfide linkages as when the strand has been weakened by alkali or if the extension is great enough to break some of the covalent bonds, then some polypeptide chains will slide past one another. This causes a permanent extension of the wool. The natural crispness of the fiber also supports it to regain its real shape.
Hydroscopic nature: 
It has the very absorbent nature because of the polarity of the peptide group, the salt linkages and the amorphous nature of the polymer system. The peptide groups and salt linkages easily attract water molecules which enter the amorphous polymer system of the fiber. In comparatively dry weather wool may develop static electricity. This is since these are hot enough. Water molecules in the polymer system support to distribute any static electricity which might develop.
Density: 
It has a comparatively low density and therefore fibers are light with regard to their visible weight.
Conductivity of heat: 
It has a low conductivity of heat and therefore makes it ideal for cold weather. The resiliency of the fiber is significant in the warmth properties of the fabric. Wool fibers do not pack well in yarns because of the crimp and scales, and this makes wool fabric process and capable of inserting much air. Air is one of the best insulators since it keeps body heat close to the body. The medulla of the wool fiber comprises air spaces that increase the insulating power of the fiber. This strand can take up moisture in vapor form. Absorbency is a factor also in the warmth of clothing. In winter, when people go from a dry indoor atmosphere into the damp outdoor air, the heat developed by the fiber in absorbing moisture keeps protecting their bodies from the impact of the cold atmosphere.
Dimensional stability: 
It has poor dimensional stability and therefore shrinks easily. Felting or shrinkage results since under mechanical action, such as agitation, friction, and pressure in the presence of heat and moisture, it tends to move root wards, and the edges of the scales interlock prohibiting the fiber from returning to its original position. This results in the fabric becoming thicker and smaller, that is it shrinks or felts.
Chemical properties of wool
Effect of acids: 
Concentrated acids damage it since they hydrolyze the salt linkages and hydrogen bonds. Dilute acids do not affect it.
Effect of alkali: 
It easily dissolves in alkaline solutions. Alkalis hydrolyze the disulfide bonds; hydrogen bonds and salt linkages of wool and cause the polymers to separate from each other, which is looked at the dissolution of the fibers. Hydrolysis of the peptide bonds of wool polymers leads to polymer fragmentation and total destruction of the strand. Prolonged exposure to alkalis causes hydrolysis of the peptide bonds of wool polymers to lead to polymer fragmentation and total destruction of the fiber.
Effect of bleach: 
Chlorine bleach is ordinary harmful to the wool. KMnO4, Na2O2 are utilized for bleaching.
Effect of sunlight and weather: 
Effect of sunlight’s ultra-violate radiation tends to yellow-white or dull colored fabrics. The ultra-violate cause the peptide and disulfide bonds to sever. This leads to polymer degradation products on the surface of the fiber. As a consequence, the strand not only absorbs more light but scatters the incident light to a greater extent. The prolonged exposure to sunlight weakens the fibers very much.
Colorfastness: 
Like cotton wool is easy to dye. Acid dyes, chrome, and mordant dyes are utilized to dye this. The dye molecules are attracted into the amorphous areas of wool.

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