Wool is the textile fiber obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have some properties similar to animal wool.
Wool is an animal fiber and consists of protein together with a small percentage of lipids. This makes it chemically quite distinct from cotton and other plant fibers, which are mainly cellulose, and akin to silk, another animal fiber composed primarily of protein.
Most wool used by the textile industry comes from sheep. Wool is also obtained from goats, camelids, rabbits, and several other mammals, although the names used for these fibres vary between industries and legal systems. After collection, wool is sorted and cleaned before it is carded or combed and made into yarn, felt, insulation, fertilizer, or other products.
Characteristics Wool is most commonly obtained from sheep. It is generally creamy white, although some breeds produce black, brown, grey, or mixed-colour fleeces. Wool grows from hair follicles, which are structures extending from the epidermis into the dermis. Primary follicles can produce kemp, medullated fibres, and true wool fibres, while secondary follicles produce true wool fibres. Kemp is coarse, usually medullated, and may be shed from the fleece. True wool is distinguished from most hair by its crimp and elasticity.
Composition and structure Wool consists mainly of keratin, with about 2–3% lipid material. Keratin is a structural protein also found in human hair and nails (anatomy). A single wool fiber consists of the cuticle, the cortex, and the medulla. Its keratin contains more sulfur than the fibroin of silk because it is rich in cystine. Disulfide bonds between cystine residues help stabilize the fibre and can be altered by heat or chemical treatment.Wolfgang Bobeth (ed.), Textile Faserstoffe: Beschaffenheit und Eigenschaften, Springer, 1993, pp. 90, 166. A fibre has an outer cuticle of overlapping scales and an inner cortex. Coarse fibres may also contain a medulla. The arrangement of different cortical cells contributes to crimp, while the scales contribute to felting.
Wool is usually approximately circular in cross-section. Fibre diameter, staple length, crimp, strength, and colour vary by breed, age, nutrition, and position on the animal. The appearance of a bundle of wool depends on more than just the diameter of its fibres: their number, alignment, colour, crimp, and degree of compression all matter too. Early optical grading was therefore better suited to comparing similarly prepared samples than to absolute measurement. The Lichtwaage was built around this comparative principle, pairing a transmitted-light scale with a separate mechanical indication. Reprinted with minor revisions. Wet wool is generally weaker than dry wool, unlike many plant fibres. Published values describe particular wool types and test conditions rather than a universal range.
Crimp Crimp refers to the strong natural wave present in each wool fiber. Wool's crimp, and to a lesser degree scales, make it easier to spin the fleece by helping the individual fibers attach, 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. The amount of crimp corresponds to the fineness of the wool fibers. A fine wool like Merino may have up to 40 crimps per centimetre (100 crimps per inch), while coarser wool like karakul may have less than one (one or two crimps per inch). In contrast, hair has little if any scale and no crimp, and little ability to bind into yarn. 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.
Felting The felting of wool occurs upon hammering or other mechanical agitation as the microscopic barbs on the surface of wool fibers hook together. Felting generally falls under two main areas, dry felting and wet felting. Wet felting occurs when water and a lubricant (especially an alkali such as soap) are applied to the wool which is then agitated until the fibers mix and bond together. Temperature shock while damp or wet accentuates the felting process. Some natural felting can occur on the animal's back.
Absorption Wool fibers readily absorb moisture, but are not hollow. Wool can absorb almost one-third of its own weight in water.Wool Facts . Aussiesheepandwool.com.au. Retrieved on 2012-08-05. Wool absorbs sound like many other fabrics.
Flammability 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;Wool History . Tricountyfarm.org. Retrieved on 2012-08-05. it forms a char that is insulating and self-extinguishing, and it contributes less to toxic gases and smoke than other flooring products when used in carpets.The Land, Merinos – Going for Green and Gold, p.46, US use flame resistance, 21 August 2008 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.
Current evidence does not identify wool fibre itself as a cutaneous allergen. Coarse fibres, especially those at or above about 30–32 micrometres, can cause mechanical irritation and itching. Contact allergy to lanolin or processing chemicals is a separate condition and is uncommon in modern wool garments.
Processing
Shearing
Sheep shearing is the process in which a worker (a shearer) cuts off the woollen fleece of a sheep. 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 grading together to maximize the return for the farmer or sheep owner. Before instrumental testing became widely available, classing depended on trained comparison of staple length, crimp, handle, colour, cleanliness, and apparent fineness. Classers could work quickly and consistently within a local grading system, but comparing results between stations was harder unless everyone used the same samples or standards. The commercial need for comparability led to both collections of reference wool and experiments with measuring devices. Wool-classers separate the wool into four main categories:
Fleece (which makes up the vast bulk) Best quality and highest value wool, often the longest and cleanest with the most uniform crimp Broken Fleece High quality, but has broken into smaller pieces than the normal fleece Bellies From the underside of the sheep, commonly stained and less dense resulting in lower value Locks Shortest pieces of fleece, often from a second cut by the shearer, and generally the lowest quality and value
Scouring
Wool straight off a sheep is known as "raw wool", "greasy wool"Preparation of Australian Wool Clips, Code of Practice 2010–2012, Australian Wool Exchange (AWEX), 2010 or "wool in the grease". This wool contains a high level of valuable lanolin, as well as the sheep's dead skin and sweat residue, and generally also contains pesticides and vegetable matter from the animal's environment. Before modern disinfection and occupational controls, raw wool could carry Bacillus anthracis spores and transmit the disease historically known as woolsorters' disease. Cuts and puncture wounds from sorting, packing, or baling contaminated fleece could let the bacteria enter through the skin. Before the wool can be used for commercial purposes, it must be scoured, a process of cleaning the greasy wool. Scouring may be as simple as a bath in warm water or as complicated as an industrial process using detergent and alkali in specialized equipment. In north west England, special potash pits were constructed to produce potash used in the manufacture of a soft soap for scouring locally produced white wool.
Vegetable matter in commercial wool is often removed by chemical carbonization. In less-processed wools, vegetable matter may be removed by hand and some of the lanolin left intact through the use of gentler detergents. This semigrease wool can be worked into yarn and knitted into particularly water-resistant mittens or sweaters, such as those of the Aran Island fishermen. Lanolin removed from wool is widely used in cosmetic products such as hand creams.
Carding, combing, and finishing After washing, wool is carded and may also be combed. Carded short-staple fibre is used for soft, bulky woollen yarn, while combed long-staple fibre is used for smoother and stronger worsted yarn. Finishing treatments can reduce felting, improve machine washability, protect against insects, or alter handle and appearance. The chlorine-Hercosett process is a common shrink-resist treatment; chlorine-free alternatives have also been developed.
Fineness and yield Raw wool has many impurities; vegetable matter, sand, dirt and yolk which is a mixture of suint (sweat), grease, urine stains and dung locks. The sheep's body yields many types of wool with differing strengths, thicknesses, length of staple and impurities. The raw wool (greasy) is processed into 'top'. 'Worsted top' requires strong straight and parallel fibres.
Common namePart of sheepStyle of woolFineShoulderFine, uniform and very denseNearSidesFine, uniform and strongDownrightsNeckShort and irregular, lower qualityChoiceBackShorter staple, open and less strongAbbHaunchesLonger, stronger stapleSecondsBellyShort, tender, matted and dirtyTop-notHeadStiff, very coarse, rough and kempyBrokesForelegsShort, irregular and faultyCowtailHindlegsVery strong, coarse and hairyBritchTailVery coarse, kempy and dirty Source:
The quality of wool is determined by its fiber diameter, crimp, yield, color, and staple strength. Fiber diameter is the single most important wool characteristic determining quality and price. At the start of the twentieth century, efforts to make fineness assessment more reproducible sometimes relied on properties that could be checked outside a laboratory. At the Icelandic wool-export station of Kolkuós there has been experimentation with combining the resistance of a small fibre sample with an optical comparison of its fineness. Before instrumental testing became common, fineness was assessed by comparing the appearance and handle of prepared samples with reference wools.
The finest and most valuable wool comes from Merino hoggets. Merino wool is typically 90–115 mm (3.5–4.5 in) in length and is very fine.(between 12 and 24 microns). Because of this, Merinos are typically graded separately from other breeds:
+Merinos Diameter in micronsName< 15.5 Ultrafine Merino15.6–18.5 Superfine Merino18.6–20Fine Merino20.1–23 Medium Merino> 23 Strong Merino The grades of wool may vary depending on the breed or purpose of the wool. Wool taken from sheep produced for meat, for instance, is typically coarser, and has fibers 40–150 mm (1.5–6 in) in length. Damage or breaks in the wool can occur if the sheep is stressed while it is growing its fleece, resulting in a thin spot where the fleece is likely to break. Different breeds have different average microns, and therefore value: