Lyocell fiber (meaning soluble fiber) is known as the green fiber of the 21st century. It uses N-methylmorpholine-N-nutrient (NMMO) as a solvent and is used for wet spinning regenerated cellulose fiber. The waste can be degraded naturally, and 99.5% of the amine oxide solvent in the production process can be recycled and reused. "Very low toxicity and no pollution to the environment". In 1980, the German Akzo-Nobel company first obtained the process and product patents, and in 1989 it was officially named by the International Committee of Man-made Fibers and Synthetic Fibers. At present, the world's production capacity is about 120,000 tons, distributed in the United States, Britain, Austria, Germany, India, South Korea and Taiwan. A. Lyocell fiber is used in clothing with its excellent wearability. It can be spun purely or blended with cotton, linen, silk, wool, synthetic fibers and viscose fibers to improve the performance of other fibers. The fabric woven by its yarn is rich in luster, soft and smooth, natural hand feel, excellent drape, good air permeability and wearing comfort. Pure Lyocell fabric has a pearl-like luster, and the inherent fluidity makes the fabric look light and thin with good drape. Different styles of pure Lyocell fabrics and blended fabrics can be woven through different weaving and knitting processes, which are used in high-end denim, ladies underwear, fashion, and men's high-end shirts, casual wear and casual wear, etc. The newly developed fine denier and super fine Denier Lyocell fiber makes it play a better role in the development of high-end products. At present, Lyocell products are becoming more and more popular in Japan, Western Europe and the United States, and sales are increasing. B. In industrial use, Lyocell fiber has higher strength, the dry strength is close to polyester, much higher than cotton, and its wet strength is almost 90% of the dry strength, which is unmatched by other cellulose fibers. It has been widely used in non-woven fabrics, industrial filter cloth, industrial yarn and special paper. Lyocell fiber can be made into non-woven fabrics with various properties by needle punching, spunlacing, wet laying, dry laying and hot bonding, which is better than viscose fiber products. Several European companies are researching the application of Lyocell fiber in sewing thread, work clothes, protective clothing, diapers, medical clothing, etc., and Japanese paper manufacturers are also developing the use of Lyocell fiber in specialty paper.

　　Lyocell fiber products in the wet state, through mechanical external force friction, will produce obvious fibrillation phenomenon, this phenomenon is manifested in the longitudinal separation of finer fibrils on the yarn surface, resulting in hairiness. The reason for fibrillation is that Lyocell fiber has a higher degree of axial orientation, and the transverse bonding force between microfibrils is weak. The high expansion of the fiber in the wet state weakens this bonding force. The weakening causes the skin fiber to fall off under the friction of the fiber itself or the metal, and the remaining skin fiber is longitudinally cracked to form longer and uneven fibrillar hairs. The characteristics of Lyocell fibrillation make the finished style of this fiber fabric have two types, one is the use of the original fiber

Fibrillation characteristics: through primary fibrillation, enzyme treatment and secondary fibrillation, a peach skin style product is produced. The other is that no secondary fibrillation is carried out after the enzyme treatment, and the surface is neat and clean. Area thing. Although the easy fibrillation performance of Lyocell fiber brings convenience to the production of non-woven fabrics, filter materials and jeanette style fabrics, it brings troubles to the production and use of smooth fabrics, such as the control of processing techniques in production, The selection of equipment and auxiliaries; the fabric is easy to fluff and pilling during use, and the color and light will change. In addition, clothing made of Lyocell fabric is severely fibrillated after many daily washings, giving the clothing a strong sense of old age.

　　Lyocell fiber performance

The main composition of 　　Lyocell fiber is cellulose like cotton or viscose. Its molecular weight and crystallinity are between cotton and viscose

　　Lyocell fiber, cotton and viscose fiber polymerization degree, crystallinity

　　 fiber cotton Lyocell fiber viscose

　　 Degree of polymerization 10000 500-550 250-300

　　 Crystallinity (%) 70 50 30

It is precisely because of the unique degree of polymerization and crystallinity of Lyocell fiber that it has three major characteristics, namely high strength, its strength is close to polyester; rapid water absorption, its water absorption speed is close to twice that of cotton, and its moisture regain is better than cotton. Self-fibrillation produces peach skin effect.

　　Part of its physical properties are shown in the figure.

　　 principle of fibrillation

　　Easily fibrillated is one of the characteristics of ordinary Lyocell fiber. Fibrillation refers to the splitting of small microfibers (1-4um in diameter) on the surface of the fiber. Generally speaking, during the first fibrillation, the fibrils produced are relatively large, usually 1mm or even longer, and can be entangled into balls. If they are not disposed of, it will affect the wearing and look and feel.

　　 is used to characterize the degree of fibrillation with the fibrillation index F.I. (Fibrillation Index), which is generally divided into 0-10 grades. The higher the grade, the more severe the fibrillation degree. Generally, when the degree of fibrillation>2, the appearance of the fabric is already unsightly.

　　 The main factors affecting the fibrillation of Lyocell fabric are the following aspects (take 100% Lyocell, 21×16 110×60, 63″ fabric as an example):

　　A, temperature

　　The higher the temperature, the greater the fibrillation index. Therefore, in order to achieve sufficient fibrillation in actual production, a higher temperature is used to improve production efficiency.

　　B, PH value

　　The increase in the pH value of the aqueous solution helps the swelling of Lyocell fiber and also facilitates its fibrillation. Therefore, in order to improve the efficiency of fibrillation, the pH value of the aqueous solution should be increased as much as possible within the possible range.

　　C, time

　　 Before the treatment time 90 minutes, the fabric fibrillation index has a linear relationship with the treatment time, that is, the treatment time increases, the fibrillation index increases, and after 90 minutes, the fibrillation index increases very slowly. Therefore, it can be considered that a fibrillation time of 90 minutes should be sufficient for this fabric under the processing conditions.

　　 secondary fibrillation

The style of 　　Lyocell fabric is to produce peach skin itself. Therefore, the dyed Lyocell fabric needs to use a secondary fibrillation process to produce secondary fibrils. The fibrils produced here should be much thinner and shorter than the fibrils produced for the first time, and be a dense layer of short fleece (commonly known as peach skin).

　　 If we fibrillate the Lyocell fabric for the first time and polish it sufficiently with biological enzymes, then the second fibrillation can produce the ideal peach skin, and the peach skin produced at this time should be retained.

　　Lyocell fiber is a new generation of regenerated cellulose fiber obtained by dissolving wood pulp in NMMO solvent system without chemical reaction and using dry spray wet process. First, the German Akzo Nobel company obtained the patent in 1978, and later it was successfully commercialized by the British Courtaulds company (later merged with Accordis) and Austrian Lenzing company (Lenzing) and launched it to markets around the world. By May 2004, Lenzing had acquired the production business of LYocell fiber (including filament and staple fiber), once monopolizing the global market. LYocell fiber entered the Chinese market in the mid-1990s, with Chinese product names such as "Tencel" and "wood pulp fiber", which triggered an upsurge in the development and production of my country's Lyocell fiber series products.

Since the production technology of Lyocell fiber was once completely in the hands of foreign companies, its price has remained high. China imported 9795t of Lyocell fiber in 2005, and the import unit price according to customs statistics was US$2616/t, which is higher than domestic cotton, polyester and viscose. Over 50% of conventional fibers such as rubber, the import price in previous years has reached 35,000 yuan/t or more. Due to cost factors, the price of subsequent textile products of Lyocell fiber in my country remains high.

　　 Since the late 1990s, Donghua University, Shanghai Textile Holding Group and other units have conducted long-term research and conducted joint research with a German research institute and achieved success. In February 2006, the first domestic Lyocell fiber was successfully produced in Shanghai Leo Development Enterprise Co., Ltd., and the 1,000t/year production line was officially put into production, breaking the original monopoly of foreign companies. It is estimated that the output of domestic Lyocell fiber will exceed 10,000 t/year around 2010. It can be predicted that with the successful localization of the fiber and the continuous expansion of output, the market price of my country's Lyocell fiber will continue to fall.

Since the dry and wet strength of Lyocell fiber is excellent, the dry strength is close to that of polyester fiber, and the drop in wet strength is small, about 85% of the dry strength. This makes Lyocell fiber strong in resistance to mechanical and chemical treatment; the breaking elongation of Lyocell fiber The rate of change in the wet state is also very small, and the elongation in the wet state is about 17%, which makes its products have good dimensional stability. These advantages make up for the shortcomings of conventional viscose fiber. At the same time, the low energy consumption and pollution-free advantages of the Lyocell fiber production process are unmatched by conventional viscose fiber, and it is a truly green fiber. The global production capacity of Lyocell fiber was less than 20,000 tons in 1992, and has now expanded to 150,000 tons per year. It is expected to reach 450,000 tons per year by 2010. The market share and influence of Lyocell fiber in the regenerated cellulose fiber family Strength will continue to increase.