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Polyvinyl alcohol fiber is a synthetic fiber made by dissolving polyvinyl alcohol in water and spinning by dry spinning or wet spinning. Polyvinyl alcohol fiber is treated with formaldehyde to make polyvinyl formal fiber, which is commonly known as vinylon. The trade name in China is vinylon.
Polyvinyl alcohol ^ was synthesized by German P.H. Herman and heinel in 1924. In the 1930s, it was made into a fiber in Germany, called syntho fil. Because it is dissolved in water, it can not be used as textile fiber. It is mainly used as surgical suture. It was not until 1939 that Japan's Ichiro Sakura and others successfully studied the heat treatment and acetalization methods of polyvinyl alcohol that it became a fiber with good heat and water resistance. The countries that produce polyvinyl alcohol fiber in the world include China, Japan, North Korea and the Soviet Union, and the products are mainly short fibers.
The properties of vinylon are quite similar to cotton, which is called synthetic cotton. The strength and wear resistance are better than cotton. The durability of its blended (1:1) fabric with cotton is 0.5 ~ 1 times higher than that of pure cotton fabric. The moisture absorption is good, and the moisture regain is 4.5 ~ 5% in the standard state; The specific gravity (1.26 ~ 1.30) is smaller than that of cotton, the thermal conductivity is lower, and the warmth retention is better; Good corrosion resistance and sunlight resistance, insoluble in general organic acids, alcohols, esters, petroleum and other solvents; It is not easy to be eaten by mold. It has little loss of intensity when it is placed in seawater for a long time, buried underground or exposed to the sun for a long time. The main disadvantage of vinylon is that it has poor heat resistance to water. It has obvious deformation and shrinkage at 110 ~ 115 ℃ in wet state. After boiling in water for 3 ~ 4 hours, the fabric is obviously deformed and partially dissolved; Poor elasticity and easy to wrinkle during taking; Poor dyeability, not bright color; The low mechanical properties at high temperature limit its application in automobile tire cord.
Vinylon staple fiber is widely used for blending with cotton, viscose fiber or other fibers or pure spinning to make knitted fabrics such as outerwear, sweater, cotton sweater, trousers, sweatshirt and so on. Canvas and cable made of vinylon are widely used because of their high strength, light weight, friction resistance and sunlight resistance; Vinylon is also suitable for making various types of fishing nets because of its good impact strength and seawater corrosion resistance; Because vinylon has good stability to various chemicals, it can be used to make work clothes or as various packaging materials and filter materials.
Polyvinyl alcohol cannot be prepared by polymerization from vinyl alcohol, because free vinyl alcohol cannot exist alone. Generally, polyvinyl alcohol is prepared by polymerization with vinyl acetate as monomer and alcoholysis of the generated polyvinyl acetate. The basic process of spinning vinylon is: preparation of spinning solution, spinning and post-processing. The process of wet spinning vinylon is shown in the production flow chart of polyvinyl alcohol staple fiber in the above figure.
In industry, the concentrated solution of polyvinyl alcohol is made with water as solvent, and then filtered and defoaming to remove mechanical impurities and bubbles in the solution. The melting temperature of polyvinyl alcohol is higher than the decomposition temperature, so solution spinning can only be used. Wet spinning is often used to spin staple fibers, while dry spinning is used to spin filaments. The post-processing of polyvinyl alcohol fiber mainly includes stretching, heat setting, acetalization, water washing, oiling, drying and other processes. Different from other synthetic fiber manufacturing processes, there is one more acetal chemical process, that is, the fiber is treated with formaldehyde, so that the hydrophilic hydroxyl groups on polyvinyl alcohol macromolecules are sealed to form polyvinyl formal. Before acetalization, the fiber had poor hot water resistance, and the shrinkage was 10% in hot water at 80 ~ 90 ℃. After acetalization, the shrinkage under the same conditions shall not exceed 2%.