1、 Linear density of wool
The linear density of wool fibers is closely related to various physical properties. Generally, the finer the wool, the more uniform its linear density, higher strength, more curly, dense scales, soft luster, high fat and sweat content, but shorter in length. Therefore, linear density is an important indicator of wool quality. Low linear density of wool fibers is beneficial to yarn strength and evenness. However, too fine wool is more prone to defects when spinning. The linear density of wool fibers is also closely related to the quality and style of wool fabrics.
The commonly used indicators of wool linear density include average diameter, quality count, and tex number. If the fiber diameter distribution can be obtained, the diameter variation coefficient can be used to represent the linear density unevenness of a batch of wool.
Wool fibers vary greatly in diameter, with the smallest pile having a diameter of about 7 μ m. The thickest diameter can reach 240 μ m。 Even on the same wool, the diameter difference can reach 5 to 6 μ m。 The reasons for the difference in wool linear density are complex, including the breed, age, gender, growth site of wool, and feeding conditions of sheep.
On the same sheep, the hair on the shoulder is the thinnest, followed by the hair on the body side, neck, and back. The hair on the front neck, buttocks, and abdomen is thicker, and the hair on the throat, lower leg, and tail is the thickest.
Quality count is an indicator of wool linear density that has been used for a long time in the wool industry. Currently, commercial transactions, grading in the wool textile industry, and the formulation of sliver making processes are based on quality counts as an important basis. In the last century, sensory methods have always been used in commerce to evaluate the quality of wool. An international conference at the end of the last century referred to the actual number of British combed wool yarns that could be spun from various linear density wool as the quality count, based on the requirements for spinning equipment, spinning technology, and wool yarn quality at that time, to indicate the quality of wool. With the development of science and technology, the improvement of spinning methods, the continuous improvement of textile quality requirements, and the progress of fiber performance research, wool quality count has gradually lost its original significance. Currently, the quality count of wool only represents the fineness index of wool with an average diameter within a certain range.
2、 Length of wool fibers
Due to the existence of natural curls, the length of wool fibers can be divided into natural length and straight length. The linear distance between the ends of a fiber bundle when it is naturally curled is called the natural length, which is commonly used to indicate the length of the tuft. The length of wool fibers after being straightened after removing curls is called the straightened length. Straight lengths are used in wool spinning production.
The length of wool fiber varies greatly depending on the breed, age, gender, growth site of wool, feeding conditions, shearing times, and season of the sheep. Generally, the length of domestic fine wool ranges from 5.5 to 9 cm, while the length of semi fine wool can reach 7 to 15 cm, while the length of coarse wool is 6 to 40 cm. On the same sheep, the hair on the shoulders, neck, and back is longer, and the hair on the head, legs, and abdomen is shorter.
When the linear density of wool fibers is the same, wool with long and regular fibers and less short wool content has better yarn strength and evenness. The length of wool is also the basis for determining the yarn count and selecting process parameters.
3、 The curl of wool
The curl of wool fibers is related to the shape of the wool blanket, the linear density, elasticity, cohesion, and fluffing properties of the fibers. Curling also has a significant impact on yarn quality and fabric style.
Wool fibers have deep and shallow curls. According to the depth of the curl, that is, the wave height, and the length, that is, the wave width, the curl shape can be divided into three categories, one is weak curl. This type of curl is characterized by less than half a circumference of the curl arc, being relatively straight along the length of the fiber, and having fewer curls. The curl of semi fine hairs mostly belongs to this type. 2 is often curled. Its characteristic is that its curly waveform approximates a semicircular shape. The curl of fine hairs mostly belongs to this type. 3 is a strong curl. It is characterized by a high amplitude of curly waves. More curls. The belly hair of fine wool sheep mostly belongs to this type. Frequently curled wool is mostly used in combed wool spinning to produce elastic and smooth surface yarns and fabrics. Strongly curly wool is suitable for rough carded wool spinning to produce woolen fabrics with a plump surface, good hand feel, and elasticity.
The index indicating the curl number of wool fibers is the curl number; The index indicating the depth of curl is the curl rate; The indicators indicating crimp elasticity include crimp recovery rate and crimp elasticity recovery rate. Their definitions, calculation formulas, and test methods will be described in Chapter 4, Chemical Fiber Crimp Inspection.
Generally, the curl number of fine wool is 6-9/cm.
4、 Moisture absorption of wool fibers
The moisture absorption of wool fibers is expressed by moisture regain. Wool has the strongest moisture absorption among common fibers. Under general atmospheric conditions, the moisture regain is between 15% and 17%.
5、 Strength and elongation of wool fibers
The tensile strength of wool fibers is the lowest among commonly used natural fibers, with a breaking length of only 9-18 km. Generally, the finer the fineness of wool, the less the medullary layer, the higher its strength.
The elongation ability of wool fibers after stretching is the largest among commonly used natural fibers. The breaking elongation can reach 25% - 35% in the dry state and 25% - 50% in the wet state. After removing external forces, the elastic recovery ability of elongation is the best among commonly used natural fibers. Therefore, fabrics made of wool are not prone to wrinkles and have good wear performance.
6、 Chemical Stability of Wool Fibers
Wool fibers are more acid resistant than alkali resistant. Dilute and concentrated acids have little damage to wool over a short period of time, so acids are often used to remove vegetable impurities such as grass dust from raw wool or wool. Organic acids such as acetic acid and formic acid are important dyeing promoters in wool dyeing. Alkali can turn wool yellow and dissolve.
