The main component of wool is keratin, which is composed of a variety of
α-amino acid residues, which can be combined into long-chain molecules in a
spiral shape, which contain carboxyl groups, amine groups and hydroxyl groups,
forming salt bonds between the molecules. and hydrogen bonds, etc. The long
chains are linked by cross-bonds formed by disulfide bonds of cystines. The
above chemical structure determines the characteristics of wool. For example,
when the long chain of wool fiber macromolecules is stretched by external force,
it transitions from α-type helical shape to β-type extension type, and then
returns to α-type after the external force is removed, then its appearance is
excellent in elongation deformation and resilience of wool. The stronger
hygroscopic ability of wool is related to some groups on the long chain. Wool is
more acid-resistant than alkali-resistant, because alkalis are prone to
disulfide groups in wool cystine, which damages the wool. Oxidizing agents can
also damage the wool by destroying the disulfide groups.
The physical properties of wool mainly include fineness, length, bending, strength and elongation, elasticity, felting, hygroscopicity, color and luster. Fineness is an important process characteristic to determine the quality and use value of wool fiber, which is expressed by the diameter of the fiber in microns or the quality count; the smaller the fineness, the higher the count, and the finer the spun wool yarn.
Length includes natural length and straight length, the former refers to the straight-line distance between the ends of the tuft, and the latter is the length measured by straightening the fibers. The elongation of the fine hair is above 20%, and the semi-fine hair is about 10 to 20%. Under the same fineness, the longer the wool, the higher the spinning performance and the better the quality of the finished product. Bending is widely used as the basis for evaluating the quality of wool. The wool with neat and consistent shape is spun into yarns and products that are soft to the touch, with good elasticity and warmth. The fine hairs have many bends and high density, and the coarse hairs are wavy or flat without bends. Strength and elongation have a direct effect on the firmness of the finished product. Strength refers to the stress of the wool to break; elongation refers to the increase in length due to the breaking force. The breaking strength of various types of wool varies widely.
The fineness of the same type of hair is proportional to its strength, and the thicker the hair, the greater the strength. The more developed the medulla with medullary hairs, the worse its ability to resist breaking. The elongation of wool is generally up to 20 to 50%. Elasticity allows the product to maintain its original form and is an indispensable characteristic of wool for carpets and blankets. The felting and hygroscopic properties of wool are generally better. The luster is often related to the state of scale coverage on the surface of the fiber. The fine hair has a weak reflection ability to light, and the luster is softer; the luster of the coarse hair is strong and shiny. Weak luster is often caused by damage to the scaly layer.