Formation of Synthetic Polymer Fibers

Z. K. Walczak, Formation of Synthetic Fibers, Gordon and Breach, New York, 1977. H. Krassig, Film to fiber technology, J, Polym. Sci.—Macromol. Rev. 12, 321 (1977). 

There also existed another use of synthetic polymers besides synthetic gels as the hard template to influence crystal growth discussed above. In this case, sohd synthetic polymers were used as a real hard template . It has been demonstrated that calcium carbonate favored the formation of the vaterite phase on the poly(vinyl chloride-co-vinyl acetate-co-maleic acid) substrate in the supersatiuated solution prepared from calcium nitrate and sodium dicarbonate solutions at pH 8.50 [238]. Commercial polymer fiber (Nylon 66 and Kevlar 29) can induce crystallization of calcite in solution, but the vaterite phase tends to crystallize on the surface of polymers in the presence of soluble polymer (PVA), and aragonite favors forming on the siuface of polymers modified with acid or alkah accompanying PVA [239]. 

Manufactured protein fibers, often called azlons, are man-made fibers produced from animal or plant proteins. Examples of protein sources are milk, chicken feathers, soy beans, peanuts, corns, etc. Traditionally, most manufactured protein fibers were made directly from proteins dissolved in solvents. Recent trends in the research and development of manufactured protein fibers include the use of biochemistry to modify the source proteins and the introduction of synthetic polymers such as polyvinyl alcohol and polyacrylonitrile to improve the fiber mechanical properties. Antibacterial agents are often being added during the fiber formation process to provide health benefits to the manufactured protein fibers. As a result, the chemical structure of manufactured protein fibers is becoming more complex. 

For this third generation of manufactured protein fibers, milk and soy beans are the two most important protein sources. Chicken feathers also are being widely used in the development. In addition to the common methods used in the first and second generations, many technical innovations have been applied to the production of these manufactured protein fibers. Examples include the use of biochemistry to modity the protein structure, the incorporation of synthetic polymers to improve the fiber strength and modulus, the formation of protein-based copolymers by chemical grafting, etc. 

The uniformity of fibers affects the properties and quality of end-products. The strength of an individual fiber is determined by its weakest point. For synthetic polymer fibers, man-made inorganic fibers and nanofibers, the uniformity can be controlled during the fiber formation process to minimize the stmctural irregularities. However, it is difficult to control the uniformity of natural fibers since the structure of these fibers is affected by many environmental factors. Although the uniformity of an individual natural fiber is uncontrollable, it is possible to improve the overall uniformity of fibers in end-products by blending natural fibers from many different batches. 

The cross-sectional shape of fibers is more complex. Many natural polymer fibers have unique cross-sectional shapes. For example, the cross-section of dry cotton is kidney-shaped, while that of degummed silk is nearly a triangle. These cross-sectional shapes are controlled by genetic codes, and human has limited influence. However, the cross-sectional shapes of synthetic polymer flbers, inorganic flbers, and nanofibers can be manipulated by controlling the fiber formation processes. The cross-sectional shapes of these fibers range from circular to oval, triangular, dog bone, trilobal or multilobal, hollow, etc. 

Synthetic polymer fibers typically are white or ofiF-white when they are manufactured. Some special synthetic polymer fibers have other types of color. For example, as-spun Kevlarfibers typically are yellow. In addition, synthetic polymer fibers with different colors also can be produced by adding pigments dining fiber formation or by dyeing after the fibers are formed. Natural cellulose and protein fibers exhibit great color difference by nature, and their color also can be modified by dyeing. 

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