Water-soluble polyvinyl alcohol (PVA) is a valuable functional differential fiber.
In 1930s, polyvinyl alcohol (PVA) fiber, which was originally developed, was made into medical surgical yarn and surgical suture in Germany by using its solubility in water.
In World War II, the United States and other countries used PVA fiber to make parachutes for laying mines.
In the 1950s, Japan began to further study the water-soluble use value of PVA fiber. By the end of the 1950s, Japan's water-soluble fiber production accounted for 20% of the total production of vinylon. In the past 20 years, there has been a new and breakthrough development, and a new type of water-soluble fiber with better performance has been developed.
China started the research and development of water-soluble fiber in the late 1970s, and made gratifying progress in recent years, which reversed the situation of dependence on imports, single product variety and low grade, and has formed large-scale production and achieved certain economic benefits.
1. Characteristics and development of water-soluble fiber
Water-soluble PVA fiber not only has ideal water-soluble temperature, strength and elongation, but also has good acid resistance, alkali resistance and dry heat resistance. After being dissolved in water, it is odorless and nontoxic, and the aqueous solution is colorless and transparent, which can naturally decompose in a short time without causing any pollution to the environment. It is a 100% green environmental protection product.
In addition, according to the recent research results, PVA is the only biodegradable material in large-scale synthetic polymers. It is precisely because of the unique water-soluble properties of PVA fiber that the development of water-soluble PVA fiber with different properties and the development of broadening its application scope are still going on. According to the hydrophilicity of PVA fiber itself, specially processed PVA fiber has water solubility that other fibers do not have. There are two kinds of water-soluble PVA fibers: filament and staple. At present, the methods of manufacturing water-soluble fibers at home and abroad are as follows:
1.1 Wet spinning
The PVA aqueous solution is sprayed into a high-concentration Na2SO4 solution for solidification, and the solidified fiber is drawn and dried under wet and hot conditions, and then drawn by dry heat and heat treatment. The advantages of this method are high yield and low cost. The use of modified PVA is also beneficial to the modification of ordinary PVA in the original solution. Its disadvantages are that the process is difficult, Na2SO4 enters the fiber surface, so it is difficult to produce PVA fiber which can be dissolved in water below 80℃ without Na2SO4 salt, and irregular defects appear on the fiber surface and internal structure due to the direct removal of solvent from the solidification solution, which limits the strength improvement.
In China, water-soluble fibers are mostly produced by wet spinning process. Due to the difficulty of this process, only water-soluble fibers with water-soluble temperature of 70℃ ~ 90℃ are produced at present, and other physical properties need to be further improved. For example, Shanghai Petrochemical Vinylon Factory has developed a water-soluble PVA； with a water-soluble temperature of 70 5℃; Sichuan vinylon factory also produces water-soluble PVA with water-soluble temperature of 80 5℃.
1.2 Dry spinning
Spray high-concentration PVA fiber solution into hot air to evaporate the solvent and solidify it into silk, and then dry-heat draft and heat treatment to obtain it.
The advantage of this method is that the spinning process is simple, and it is suitable for producing many kinds of water-soluble filaments, especially for producing water-soluble fibers at room temperature. However, this method has some disadvantages, such as low denier of fiber tow, low yield and high cost.
1.3 Melt and semi-melt spinning
Adding a certain amount of water to plasticize PVA, then making it semi-molten at a low temperature (120℃ ~ 150℃), pressing it out of the spinneret with great pressure, and then cooling and solidifying it in the air. This method can be used to spin monofilaments or multifilaments, but it has not been widely used in industrial production so far.
1.4 Boric acid gel spinning
PVA gel solution with boric acid added was extruded into NaOH and Na2SO4 solution for molding and crosslinking. Cross-linked fibers are prepared by drafting, neutralization, water washing, drying, dry-hot drafting and heat treatment under hot and humid conditions. The crosslinking of this kind of fiber can make the water-soluble PVA fiber have good stability in the medium humidity atmosphere, but it will be hydrolyzed and detached quickly in water, so its water solubility will not be affected.
1.5 Gel spinning
The new method of freezing glue yarn developed by Japan Cola Company is that PVA is dissolved in an organic solvent with good solubility as the spinning dope, which is squeezed into the coagulation liquid of the organic solvent from the spinneret hole and quickly cooled into a gel, so that the dope trickle forms a stable structure before the solvent is removed, and the solidified fiber has a uniform circular cross-sectional structure. This method can obtain PVA fiber with low alcoholysis, high strength, low shrinkage and not easy to glue. The characteristic of this method is that there is no water in the whole process, and the solvents and coagulants used are all organic solvents, and the solvents have wide polymer solubility, so different kinds of polymer fibers can be produced by the same production process.
The whole process is completed in a closed system, in which the solution is completely recycled, no waste liquid is discharged, and the environment is not polluted. A new type of water-soluble PVA fiber K-Ⅱ has been successfully produced by this method. Its water-soluble temperature is 0 ~ 100℃, and it also has biodegradability, alkali resistance, pressure and heat resistance, high strength, low shrinkage, high flame retardancy and easy fibrillation.
2. Application of water-soluble fiber in textile industry
The water-soluble fiber is blended with other fibers as intermediate fiber, and the water-soluble fiber is dissolved after textile processing to obtain high-count and high-grade textiles. In April, 1997, IWS cooperated with Japan's KURARAY Company to introduce the wool manufacturing technology of "wool/polyvinyl alcohol" to the world wool industry by using the excellent water solubility of new water-soluble PVA fiber K-Ⅱ at room temperature, and it has entered the market. It uses wool with low count and water-soluble PVA fiber to blend, and after spinning and weaving into grey cloth, PVA fiber is removed in the finishing process, thus making high-count, light and high-grade pure wool fabric, creating a new era of low-cost and high-quality pure wool fabric. China has also used domestic water-soluble PVA fiber to produce batches of high-grade linen fabrics and high count light and pure wool fabrics.
Water-soluble fiber is used for warp sizing of fabric, which has the advantages of uniform sizing, stable chemical structure, good corrosion resistance and simple process. Weft-free blanket is made by weaving water-soluble fiber as weft and dissolving the weft in hot water. This method is also suitable for warp knitting, which is beneficial to the knitting of clothes. In addition, water-soluble fibers are also used in the production of untwisted yarns, knitwear tailoring, and special work clothes for national defense.
Water-soluble nonwovens are mainly used as the skeleton materials for embroidery in clothing industry, which can be embroidered on them alone or used together with clothing fabrics. After processing, as long as the nonwovens are treated in hot water, the embroidered patterns can be retained. The development and application of water-soluble fiber is particularly important in wool spinning industry. Now, Japan's KURARAY Company sends the relevant information of wool manufacturing technology of "wool /PVA" to wool manufacturers all over the world. In Japan, we have established contacts with 30 wool companies, and overseas, we have established contacts with more than 100 companies in more than 20 countries. Four or five big companies in Italy have started selling.
It is reported that the International Wool Bureau has held technical lectures in Beijing, Shanghai and other places to introduce the manufacturing technology of "wool /PVA", which has attracted the attention of the domestic wool spinning industry. At present, relevant enterprises show great interest in the production and application of low-temperature water-soluble PVA fiber. In addition, KURARAY Company is studying the new composite materials of "KURALON K-II" water-soluble fiber, natural fiber such as cotton and hemp, and high-performance fiber such as polyamide fiber, fluorine fiber and carbon fiber.
Although these high-performance fibers have some special excellent properties, due to the shrinkage, strength and oil finish of these fibers, there will be some difficulties in various processes such as spinning and weaving, which will be improved by compounding with "KURALON K-II" water-soluble fibers.
The research on water-soluble fiber in China only started in 1979. Although it started late, it has attracted more and more attention, especially in recent years, it has been welcomed by users in wool spinning, linen spinning, embroidery and other industries.
We should continue to strengthen the research on the process of producing water-soluble fiber, and we need to strengthen, improve and further expand the water-soluble fiber in terms of variety, quality and application.
Water-soluble fiber has great market potential. Therefore, it is necessary to develop water-soluble fiber that meets the market demand and has excellent performance by reforming and updating equipment and constantly adjusting the optimization process, so as to gradually catch up with the development pace of water-soluble fiber abroad.