Filament cross-section shape

Yarns and Fibers. Many different acetate and triacetate continuous filament yams, staples, and tows are manufactured. The variable properties are tex (wt in g of a 1000-m filament) or denier (wt in g of a 9000-m filament), cross-sectional shape, and number of filaments. Individual filament fineness (tex per filament or denier per filament, dpf) is usually in the range of 0.2—0.4 tex per filament (2—4 dpf). Common continuous filament yams have 6.1, 6.7, 8.3, and 16.7 tex (55, 60, 75, and 150 den, respectively). However, different fabric properties can be obtained by varying the filament count (tex per filament or dpf) to reach the total tex (denier). 

Yarns and Fibers. Many different acetate and triacetate continuous filament yams, staples, and lows are manufactured. The variable properties are tex (wt in g of a 1000-m filamenit or denier [wt in g of a 9000-m filament), cross-sectional shape, and number of filaments. Individual... 

In the past, surface tension was observed as a major factor responsible for the filament cross-sectional shape (Ziabicki, 1967 Takarada et al., 2001 Rawal and Davies, 2005 Rawal and Davies, 2006). However, an increase in the cooling rate along with a higher viscosity of the melt can significantly reduce the deviation of the filament shapes from their corresponding slot geometries. 

Although the cross-sectional shape of the spinneret hole direcdy affects the cross-sectional shape of the fiber, the shapes are not identical. Round holes produce filaments with an approximately round cross section, but with crenelated edges triangular holes produce filaments in the form of a "Y." Different cross sections are responsible for a variety of properties, eg, hand, luster, or cover, in the finished fabric. Some fibers may contain chemical additives to provide light-fastness and impart fire retardancy. These are usually added to the acetate solution before spinning,... 

Textile fibers must be flexible to be useful. The flexural rigidity or stiffness of a fiber is defined as the couple required to bend the fiber to unit curvature (3). The stiffness of an ideal cylindrical rod is proportional to the square of the linear density. Because the linear density is proportional to the square of the diameter, stiffness increases in proportion to the fourth power of the filament diameter. In addition, the shape of the filament cross-section must be considered also. For textile purposes and when flexibiUty is requisite, shear and torsional stresses are relatively minor factors compared to tensile stresses. Techniques for measuring flexural rigidity of fibers have been given in the Hterature (67—73). 

More akin to silk yarns, continuous filament POY produces lighter fabrics, typically of 100 % PET. Such yarns have provided a fertile field for imaginative engineering of cross-sectional shapes, fiber sizes and combinations of color and texture. An entire field of specialty filament yarns known as Shingosen has been developed in Japan, providing novel and luxurious fabrics that cannot be duplicated with natural fibers. 

Modified Cross Sections. Nylon filaments are spun in a variety of cross-section shapes that include the conventional round to irregular solid and hollow shapes (Fig. 13). The cross-section shape is an important variant in designing the functionality and luster of fibers. The round cross section is used for strength in industrial applications and for subdued luster in apparel and upholstery. The multilobal cross sections are used to enhance bulk and for bright luster in both BCF and spun staple yams for carpets and upholstery. The grooves in the multilobal shapes also enhance moisture transport by wicking water through capillary action. Flat-sided ribbon-like cross sections provide cover in apparel applications. 

The spinnerette is stainless steel, and because the filaments must be heated and prevented from sticking together, and because space must be allowed for the escape of acetone vapor, the holes must be kept farther apart than those of the spinnerettes used for wet spinning. As the hot solution of cellulose acetate in acetone emerges downward into the spinning cabinet, an instantaneous loss of acetone takes place from the surface of the filaments, which tend to form a solid skin over the still liquid or plastic interior. A current of air, either in the direction the filaments are moving or countercurrent, heats the filaments, and as the acetone is diffused from the center through the more solid skin, each filament collapses to form the indented cross-sectional shape typical of cellulose... 

A stream tube, or stream filament, is a tube of small or large cross section and of any convenient cross-sectional shape that is entirely bounded by streamlines. A stream tube can be visualized as an imaginary pipe in the mass of flowing fluid through the walls of which no net flow is occurring. 

Spandex has better mechanical and physical properties than rubber fiber in terms of tenacity, modulus, anti-aging, linear density, and dye ability. Dry spun spandex has round, oval, or dumbbell shaped filament cross-sections, while wet spun spandex has mainly irregular filament profiles. In some spandex fiber, the filament fusion can be so strong that fibers merge into one another. Melt spun spandex is produced as monofilaments or multifilaments of predominantly round cross-sections and smooth surface. 

An outline of the viscose process is shown in Figure 10.52. By this process, short-fibered cellulose (wood pulp) is converted in a series of controlled and coordinated steps to a spinnable solution and then into longer filaments, which may be precisely controlled as to length, denier, cross-sectional shape [118], and other physical properties. 

Tow properties are influenced by the shape of the filament cross section, dpf, and total denier, and the crimp imparted to the tow. The tow properties in turn control the properties of the cigarette filter. Important filter properties of weight, firmness, pressure drop, smoke-removal efficiency and cost are controlled by the fiber and tow properties [15,85,86]. 

The cross-sectional shape of the filament relates to the volumetric transfer rate of the spin bath liquid (non-solvent) into the fiber versus the outward transfer of the solvent [98,99]. The fiber skin being the first portion to undergo coagulation, limits the volume that the fiber can occupy and, if less volume of solvent diffuses out, the fiber becomes non-circular and progresses towards a kidney bean shape. Each manufacturer uses a different spinning process and the filament cross-section is a useful fingerprint to identify the manufacturing source. 

The polymer dope concentration in the spinning solvent is normally about 15% w/w, which controls the effectiveness, efficiency and economics of the spinning process, whilst the temperature controls the spinning and can also control the final cross-sectional shape of the spun filament. The highest dope concentration ensures that lesser solvent has to be recovered per kg of fiber produced, but if too high, the viscosity would make filtration and spinning difficult. 

Hot and cold methods are also used to create synthetic fibers. A strand of fiber is a single filament that can be combined or spun with other filaments to create the final fiber product. The process from raw polymer to final product is called spinning, as illustrated in Figures 13.39 and 13.40. The cross-sectional shape of the strands is dictated by the shape of the orifice through which is it extruded. As shown in Figure 13.39, extruded fibers are spun together into a filament (bundle of fibers) that can be cut into smaller staple fibers with lengths on the order of centimeters or less that may be further processed into textile materials. ... 

The method of resonance vibrations (Section C above) has also been used, in the form of standing longitudinal wave measurements and flexural vibrations of short fiber segments. - In the latter case, the fiber cross-section shape and dimensions must be known with high accuracy the equations for calculating E and E" are similar to equations 12 and 13 (for circular cross-section) but with different numerical coefficients for one end clamped and one free. Despite the small flexural stiffness of thin fibers, this method has been employed on filaments as thin as 0.03 mm . 

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