Main Components
The main component of wool is keratin, which is composed of various α-amino acid residues. These residues can be linked into long, helical chains containing carboxyl, amino, and hydroxyl groups, forming salt bonds and hydrogen bonds between molecules. The long chains are linked by cross-links formed by disulfide bonds of cystine. This chemical structure determines the properties of wool. For example, when the long chains of wool fiber macromolecules are stretched by external force, they transition from an α-helical shape to a β-extended shape, and then return to the α-shape after the force is removed. This results in excellent elongation deformation and resilience of wool. Wool's strong moisture absorption capacity is related to some groups on its side chains. Wool is more resistant to acids than alkalis because alkalis easily decompose the disulfide groups in cystine, damaging the wool. Oxidizing agents can also destroy disulfide groups, damaging the wool.
Physical Properties
The main physical properties of wool include fineness, length, crimp, strength, elasticity, felting properties, moisture absorption, color, and luster. Fineness is a crucial technological characteristic determining the quality and usability of wool fibers, expressed in micrometers (µm) as fiber diameter or count. The smaller the fineness and the higher the count, the finer the yarn produced. Length includes natural length and stretched length; the former refers to the straight-line distance between the two ends of the fiber bundle, while the latter is the length measured after the fiber is straightened. Fine wool has an elongation rate of over 20%, while semi-fine wool is around 10-20%. At the same fineness, longer wool results in higher spinning performance and better finished product quality. Crease is widely used to assess wool quality; wool with uniform crimp produces yarn and products that are soft to the touch, elastic, and warm. Fine wool has a high crimp count and density, while coarse wool has wavy or flat, uncreased hair. Strength and elongation directly affect the strength of the finished product. Strength refers to the stress on the wool at break; elongation refers to the increase in length due to the breaking force. The breaking strength varies greatly among different types of wool. For wool of the same type, fineness is directly proportional to its absolute strength; the coarser the wool, the greater its strength. The more developed the medulla in medullary wool, the weaker its breaking resistance. Wool elongation generally ranges from 20% to 50%. Elasticity allows products to maintain their original shape and is an indispensable characteristic of wool used in carpets and blankets. Wool generally has excellent felting and moisture absorption properties. Luster is often related to the state of the scales covering the fiber surface; fine wool reflects light less and has a softer luster, while coarse wool has a strong and bright luster. A weak luster is often caused by damage to the scale layer.
