Wool Fibers and its source
Wool, common name applied to the soft, curly fibres obtained chiefly from the fleece of domesticated sheep, and used extensively in textile manufacturing.
Wool, common name applied to the soft, curly fibers obtained chiefly from the fleece of domesticated sheep, and used extensively in textile manufacturing. Wool may be differentiated from hair mainly by the nature of the scales that cover the outer surface of each fiber.
Wool scales are numerous, minute, and pointed and are attached only at their bases; thus the fibers interlock under pressure (see Felt). The number of scales varies with the fineness and curliness of the fiber. Because of its crimp, or curl, wool has considerable resilience. This quality, together with its high tensile strength and elasticity, gives fine woolen fabrics the ability to retain shape better than cloth made from other natural fibers. Other characteristics of wool, which make it especially desirable for clothing, are its lightness, its ability to absorb moisture, and its insulating properties.
Wool production begins with several basic concepts. Along with the fiber diameter, the fiber length, and the amount of vegetable matter and any other foreign material in the fleece affect wool quality. Fiber diameter varies by breeds of sheep and is used to determine the use of the wool. Wool made up of smaller diameter fibers or fine wool is used for clothing while wool made up of larger diameter fibers or coarse wool is used for carpets and rugs. Below are more details about wool production and wool quality.
Wool Yield
As wool comes off the sheep it is called grease wool. This is because the lanolin in the wool gives it a greasy feel and appearance. This wool also contains vegetable matter, dirt, and other impurities. Wool goes through a scouring process to remove the grease, dirt and other impurities, and a carbonization process to remove vegetable matter. The difference between the grease wool weight and the clean weight is the yield. In general, fine wool fleeces have a lower yield than medium and coarse wool fleeces. Much of this also depends on the amount of grease in the fleece. Expected yields range from 45% to 70%.
Fiber Diameter
Fiber diameter is probably the most important factor for determining the quality of wool and its value. As the fiber diameter increases, it changes the way wool is used. Larger diameter fibers do not work well in the felting process, but because they are stronger and less likely to break during the carding and combing process, they are very well suited for carpets and rugs. Small diameter fibers or fine wool are best suited for clothing and textiles.
Fiber diameter is used to determine the wool grade. The American system began by visually appraising the wool fibers. This system is known by the blood grade because it starts with the Merino breed and the wool from other breeds is graded according to the percentage of Merino in the breed. Table 1 shows the various wool grades using both the American Blood Grade system and the ASTM (American Society for Testing and Materials) standard grade. The number corresponding to the ASTM grade related to the number of 560 yard lengths of yarn that can be spun from one pound of a top (clean wool).
Crimp is another wool characteristic highly related to fiber diameter. Crimp is the waviness of the wool. High-crimp wools that are very uniform are normally the higher quality wools. However, wool with too much crimp can cause problems in the processing the same as wools with very little crimp. Low-crimp wools tend to tangle and felt during scouring while high crimp wools can form balls or “neps” during carding and combing.
Vegetable Matter
Vegetable matter in wool comes from feed particles as well as burs, seeds, twigs, leaves, and grasses. Vegetable matter is removed from a fleece using a process called scouring. A certain amount of vegetable matter is expected in wool, however, an excessive amount is considered a defect and the wool may be discounted in price.
Several ways to minimize the amount of vegetable matter in wool include the following: removing belly wool, wool on the top of the head and around the cheeks, and removing manure clumps or tags. Carefully feeding sheep to prevent contamination can also decrease the amount of vegetable matter in the wool.
Fiber Length and Strength
The staple or fiber length affects how the wool can be used. Very short fibers are used in the felting process. There are three classes of staple length: staple, French combing, and clothing. The length of the wool fiber has a direct effect on spinning speed, yarn count, and yarn quality.
Fiber Color
The whiteness of wool is very important if the fibers are not expected to be dyed or will be dyed a light color. White wool fleeces come from fleeces that have been skirted to remove any urine or feces-stained wool. Producers who wish to market a very high-quality wool keep their sheep covered year-round to prevent contamination and discoloration of the wool. The presence of colored fibers in wool has an effect on the price of that wool also due to limiting the uses of the wool. These fibers can come from the sheep themselves, either dark fibers in the wool or from head, belly or legs. They may also come from stained wools. Colored wools from natural colored sheep are generally a specialized market for people who spin or weave by hand. Sold to a mainstream market, these wools are discounted because of their limited use in the dying process.
Cotted or Felted Fleeces
Occasionally, the wool fibers may become matted or felted together. This occurs when fine fibers have a very little crimp. Cotted or felted fleeces are considered low quality because of the amount of waste produced during carding due to breaking the fibers when they are torn apart. Fine wool sheep that have very little crimp should be culled.
