Wool, like other animal fiber's including human hair, grows in a follicle. During the growth, the wool fiber is covered with a natural grease (wool grease). Wool grease is secreted by the sebaceous glands, the purpose of which to both lubricate the fiber during growth and then to provide protection to the sheep by acting as a waterproofing agent against the elements of nature, such as rain, hail or snow.
Wool grease is a valuable by-product because it contains lanolin, and after being removed from the greasy wool during the raw wool scouring (washing) process, it is then extracted from the waste effluent and then sold onto the pharmaceutical industry, for use in the manufacture of cosmetic products.
Like in the case of humans, sweat is released from the sweat glands when the sheep perspires. The purpose of this is to induce a cooling effect. The sweat is produced by sheep is known as suint, which as in the case of wool grease is subsequently removed from the wool during the raw wool scouring operation.
Wool has a rather complex structure, consisting of two main types of cells: Cuticle cells and Cortex cells. For coarser wool with large fiber diameter, a third type of cell is present known as a central medulla.
Cuticle Cells
The cuticle cells are located on the outside of the fiber, and comprise of a protective layer of scales that are unique to wool and wool-like fibers. These scales overlap each other rather like the tiles on a roof of a house.
The purpose of the scale structure when the wool is still on the sheep's back is to assist in expelling dirt. The exposed edges of the scales face away from the root end of the fiber, resulting in more friction when you rub the fiber in one direction in comparison to the other. This is known as the Directional Friction Effect. This leads to a unique phenomenon known as felting, which only occurs with wool and wool-like fibers having a similar scale structure.
Felting occurs when the wool fibers are aligned in different directions, and are subjected to mechanical action, which causes them to become entangled, and eventually forming a felt.
Although felting is desirable in some products such as billiard cloths and piano key beds, in most apparel products it is unwanted as it causes shrinkage of the garment upon washing. However today, easy care technology is well established in the wool manufacturing industry to prevent felting shrinkage.
Cortical Cells
The cortical cells make up the internal part of the backbone of the wool fiber and account for about 90% of its mass. There are two main types of cortical cells known as the ortho-cortex and para-cortex. Each has a different chemical composition. In finer wool fibers these two different types of cells form into distinct halves. Because both absorb moisture at different rates, this causes the wool fiber to blend, creating crimp in the wool. In coarser wool fibers, the two different types of cells are formed more randomly, resulting in coarser wool fibers in comparison to finer ones having less crimp.
The cortical cells are cemented together by a cell membrane complex made up of proteins and waxy lipids. Inside the cortical cells are long filaments called macro fibrils, which are made up of even finer filaments known as micro fibrils. These provide the wool fiber with its strength. The macro and micro fibrils are surrounded by a matrix, which consists of proteins high in sulfur content. Because sulfur atoms attract water, it is the matrix region of the wool fiber, which provides wool with its property to absorb up to 30% of moisture by weigh without feeling wet. The matrix region is also responsible for wool inherent flame retardant and anti-static properties. In addition, the matrix enables wool to absorb and retain large amounts of dye, thus producing high intense and deep depths of colour.
Finally within the twisted molecular chains of the macro and micro fibrils, are very small protein chains which are coiled in a helical shape and act like a spring. These helix or helical coils provide wool with flexibility, elasticity and resilience, providing comfort for the wearer, and at the same time helping the wool fabric to maintain its shape, and remain crease resistant during wear.
Central Medulla
Unlike fine wool fiber, coarser wool and some medium diameters fibers may have a medulla located and running the length of the center of fiber. It is usually made up oval shaped cells filled with air.
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