Introduction of Wool Yarn
Wool yarn is an important yarn variety in the textile industry. It has the advantages of good elasticity, strong hygroscopicity and good warmth retention. However, due to the high price, it is not used much for the production of fabrics.
The history of human use of wool can be traced back to the Neolithic Age, spread from Central Asia to the Mediterranean and other parts of the world, and has become the main textile raw material in Asia and Europe. Wool fiber is soft and elastic, and can be used to make woolen, wool, blanket, felt and other daily and industrial textiles. Wool products have the characteristics of plump hand feeling, good warmth retention and comfortable wearing. The countries with the largest output of sheep wool yarn in the world include Australia, New Zealand, Argentina, China and so on. Sheep wool is divided into five categories according to fineness and length: fine wool, semi-fine wool, long wool, hybrid wool, and coarse wool. Chinese sheep wool varieties include Mongolian wool, Tibetan wool and Kazakh wool. The performance and quality of wool yarns spun from different wools are different. The main factors for evaluating wool quality are fineness, curl, color, strength and weed content.
Quality characteristics of wool yarn
wool fiber linear density
The linear density of wool fiber has a great relationship with various physical properties. Generally, the finer the wool, the more uniform its linear density, the higher the strength, the more curls, the denser scales, the softer luster, the higher the fat and sweat content, but the shorter the length. Therefore, linear density is an important indicator to determine the quality of wool yarn. The low linear density of wool fiber is beneficial to the strength and evenness of the finished wool yarn. But 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.
Commonly used indicators of wool linear density are average diameter, quality count and tex number. If the distribution of fiber diameters can be obtained, the variation coefficient of diameter can be used to represent the uneven linear density of a batch of wool.
Wool fibers vary widely in diameter, with the thinnest fluff having a diameter of about 7 μm and the thickest up to 240 μm. Even on the same wool, the difference in diameter can reach 5-6μm. The reasons for the difference in wool linear density are very complex, including the breed, age, sex, growth part of the wool and feeding conditions of the sheep.
On the same sheep, the hair on the shoulders is the thinnest, the hair on the sides, neck, and back is second, the hair on the fore-neck, buttocks, and abdomen is thicker, and the hair on the throat, lower legs, 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 yarn industry. At present, the commercial transactions, the grading in the wool spinning industry, and the formulation of the sliver-making process are all based on the quality count. In the last century, the quality of wool has been assessed commercially by sensory methods. In an international conference at the end of the last century, according to the requirements of spinning equipment and spinning technology and the quality of wool yarn at that time, the number of inch worsted wool yarns that can actually be spun by wool of various linear densities is called the quality count, which is used to represent wool. The pros and cons of 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 indicates the fineness of wool with an average diameter within a certain range.
length of wool fiber
Due to the existence of natural crimp, wool fiber can be divided into natural length and straight length. Under the natural curl of the fiber bundle, the straight line distance between the two ends is called the natural length, which is generally used to indicate the length of the tuft. The length of the wool fiber after the crimp is removed is called the straightened length. Straight lengths are used in wool yarn production.
The length of wool fibers varies greatly depending on the breed, age, sex, growing part of the wool, feeding conditions, shearing times and seasons. Generally, the length of fine wool produced in China 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, and the hair on the head, legs and belly is shorter.
When the linear density of wool fibers is the same, the wool yarns spun from wool with long and neat fibers and less short hair content have better strength and evenness. The length of wool is also the basis for determining spinning characteristics and selecting process parameters.
Curly of wool
The curling of wool fibers has a certain relationship with the shape of the quilt, fiber linear density, elasticity, cohesion and milling. Crimping also has a large impact on the quality of wool yarn and the final fabric style.
The curling of wool fibers can vary from deep to shallow. According to the depth of the curl, that is, the height of the wave, and the length, that is, the width of the wave, the curl shape can be divided into three categories. One is weak curl. The characteristics of this type of crimp are that the arc of the crimp is less than half a circumference, and the length of the fiber is relatively straight and the number of crimps is small. The curls of semi-fine hairs are mostly of this type. The second is often curled. It is characterized by a curled waveform that approximates a semicircle. The curls of fine hairs are mostly of this type. The third is strong curl. It is characterized by higher volatility in curls. More curls. Fine wool wool is mostly of this type. Often crimped wool is mostly used in the spinning of combed wool yarn, spinning wool yarn and wool fabric with elasticity and smooth surface. Strongly crimped wool is suitable for the spinning of carded wool yarn, and the spinning surface is full of fluff, good hand feeling and elastic wool.
The index indicating how much the wool fiber is crimped is the number of crimps; the index indicating the depth of the crimp is the crimp rate; the index indicating the crimp elasticity is the crimp recovery rate and the crimp elastic recovery rate. Generally, the number of crimps of fine wool is 6~9 pieces/cm.
Hygroscopicity of wool fibers
The hygroscopicity of wool fiber is expressed by moisture regain. The hygroscopicity of wool yarn is the strongest among common yarns. Under normal atmospheric conditions, the moisture regain is 15% to 17%.
Tenacity of wool fibers
The tensile strength of wool fibers is the lowest among the commonly used natural fibers. Generally, the fineness of wool is finer, and the less medulla layer, the higher its strength. The elongation ability of wool yarn after drawing is the largest among the commonly used natural fiber yarns. The elongation at break can reach 25%~35% in dry state and 25%~50% in wet state. After removing external force, the elastic recovery ability of elongation is the best among the common natural fiber yarns, so it is woven with wool yarn. The fabric is not easy to produce wrinkles and has good wearing performance.
Chemical stability of wool fibers
Wool fiber is more acid-resistant than alkali-resistant. Dilute acid and concentrated acid do little damage to wool in a short time, so acid is often used to remove plant impurities such as grass clippings in raw wool or woolen billet. Organic acids such as acetic acid and formic acid are important dye accelerators in wool dyeing. Alkali will yellow and dissolve wool.