Quality characteristics of wool fiber
1. Linear density of wool
The linear density of wool fiber is closely related to various physical properties. Generally, the finer the wool, the more uniform its linear density, higher strength, more curls, denser scales, softer luster, higher fat and sweat content, but shorter length. Therefore, linear density is an important indicator that determines the quality of wool. The low linear density of wool fiber is beneficial to yarn strength and yarn evenness. However, wool that is too fine is more prone to defects when spun. The linear density of wool fibers is also closely related to the quality and style of wool fabrics.
Commonly used indicators indicating 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 express the linear density unevenness of a batch of wool.
The diameter of wool fibers varies greatly. The diameter of fine villi is about 7μm, and the diameter of thick ones can reach 240μm. Even on the same piece of wool, the diameter difference can reach 5~6μm. The reasons for the difference in wool linear density are complex, including sheep breed, age, gender, hair growth location and feeding conditions, etc. On the same sheep, the hair on the shoulders is thinner, followed by the hair on the sides, neck, and back, the hair on the front neck, buttocks, and abdomen is thicker, and the hair on the throat, lower part of the calf, and tail is thicker.
Quality count is an indicator of wool linear density that has been used in the wool industry for a long time. Current commercial transactions, grading in the wool spinning industry, and formulation of strip-making processes all rely on quality count as an important basis. In the last century, sensory methods have been used commercially to evaluate the quality of wool. An international conference at the end of the last century called the number of British combed wool yarns that could actually be spun with various linear densities of wool based on the level of spinning equipment and spinning technology as well as wool yarn quality requirements at that time called the quality count to express wool. quality. 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 meaning. At present, the quality count of wool only represents the fineness index of wool with an average diameter within a certain range.
Table 3-1 The relationship between wool quality count and average diameter
2. The length of wool fiber
Due to the existence of natural curl, the length of wool fiber can be divided into natural length and straight length. When the fiber bundle is naturally curled, the straight-line distance between the two ends is called the natural length, which is generally used to indicate the length of the hair bundle. The length of wool fiber after removing the curl and straightening is called straight length. Straight lengths are used in woolen production.
The length of wool fiber varies greatly with the breed, age, gender, hair growth location, feeding conditions, shearing times and seasons of the sheep. Generally, the length of domestic fine wool is in the range of 5.5~9cm, the length of semi-fine wool can reach 7~15cm, and the length of coarse wool is 6~40cm. On the same sheep, the hair on the shoulders, neck and back is longer, while the hair on the head, legs and abdomen is shorter.
When the linear density of wool fibers is the same, wool with long and neat fibers and less short hair content will have better yarn strength and evenness. The length of wool is also the basis for determining the spinning characteristics and selecting process parameters.
3. Wool curl
The curl of wool fiber has a certain relationship with the shape of wool, fiber linear density, elasticity, cohesion and shrinkage. . Curl also has a great impact on yarn quality and fabric style.
The curls of wool fibers vary from deep to light. 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. The characteristic of this type of curl is that the arc of the curl is less than half a circle, relatively straight along the length of the fiber, and the number of curls is small. Semi-fine hair curls mostly fall into this category. 2 is often curled. It is characterized by a curly wave shape that approximates a semicircle. Curly fine hair mostly belongs to this type. 3 is strong curl. It is characterized by a higher amplitude of curls. More curls. Most fine wool sheep belly hair belongs to this type. Frequently curly wool is mostly used in combed wool spinning to spin yarns and fabrics with elasticity and smooth surfaces. Strongly curled wool is suitable for carded wool spinning to produce woolen fabrics with a full surface, good hand feel and elasticity.
The indicator indicating how much wool fiber is curled is the crimp number; the indicator indicating the depth of the curl is the curl rate; the indicator indicating the curl elasticity is the curl recovery rate and the curl elastic recovery rate. Their definitions, calculation formulas and test methods will be described in the crimp test of chemical fibers in Chapter 4.
Generally, the number of curls of fine wool is 6~9/cm.
4. Hygroscopicity of wool fiber
The hygroscopicity of wool fiber is expressed by moisture regain. Wool has the strongest hygroscopicity among common fibers. Under general atmospheric conditions, the moisture regain rate is 15% to 17%.
5. The tensile strength of wool fiber
The tensile strength of wool fiber is the lowest among commonly used natural fibers, and its breaking length is only 9~18km. Generally, the finer the wool, the less the medulla layer, the higher the strength.
The elongation capacity of wool fiber after stretching is the largest among commonly used natural fibers. The elongation at break can reach 25%~35% in dry state and 25%~50% in wet state.�After external force is removed, the elastic recovery ability of elongation is the best among commonly used natural fibers, so fabrics woven with wool are not prone to wrinkles and have good wearing properties.
6. Chemical stability of wool fiber
Wool fiber is more acid-resistant than alkali-resistant. Dilute acids and concentrated acids will not cause much damage to wool in a short period of time, so acids are commonly used to remove plant impurities such as grass clippings in raw wool or wool. Organic acids such as acetic acid and formic acid are important dye accelerators in wool dyeing. Alkali will yellow and dissolve wool.
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