Fibers textile

Fibers have been produced from a wide range of polymers (Appendix III). A handy listing of common textile fibers is found in the Textile World Manmade Fiber Chart, issued each year by Textile World [17]. This comprehensive chart lists the various fiber names, types, optical micrographs of cross sections and longitudinal views, mechanical properties, etc., of about 35 textile fibers. 

It may be difficult to know which fringe is correct if the dispersion of the birefringence of the fiber is different to that of the compensator. A useful trick is to cut a wedge at the end of the fiber and count the number of fringes along the wedge, which is the number of full orders of path difference [21]. The additional partial order is measured with a compensator [22] (Section 3.4.3). 

The scanning electron microscope has proven to be a very useful instrument for the assessment of fiber morphology. The three dimensional images produced clearly show surface features, such as the presence of surface modifications, finish applications, wear and the nature and cause of fiber failure. The great depth of field, simple specimen preparation and high resolution have resulted in the SEM providing a major contribution to the study of textile fibers. 

Textile fibers generally have a surface finish applied following spinning to aid handling of the fibers for production of yarns and fabrics and to 

Textile fiber fractography was initially developed at UMIST (University of Manchester Institute of Science and Technology), especially by Hearle. Fiber fractography and the classes of fracture were reviewed by Hearle and Simmens [15] and further defined later [29, 30]. These classes are shown in Table 5.1 with examples and appropriate references. The mechanism of fiber failure can be determined by fractography studies (Section 4.8.1) in the SEM. Typically, fibers broken during a standard physical test, such as 

When fibers are observed in the 45° position between crossed polarizers (polars), the change in thickness from the center to the fiber edge produces a series of polarization bands or fringes. An example of these fringes is shown 

Birefringence provides a measure of the local orientation of a material (i.e., the mean orientation of monomer units). The relation between orientation and birefringence was known from early studies of polystyrene filaments, which described both the theory and measurement [23, 25]. They showed that the orientation was greater at the surface than in the core. Mechanical properties, such as tensile strength and elongation at break, have been shown to 

The scanning electron microscope (SEM) has proved to be a very useful instrument for the assessment of fiber morphology. The three dimensional images produced clearly show surface features, such as the presence of surface 

Scanning electron microscopy micrographs taken in the normal mode do not always permit effective observation of features on fiber surfaces. Display modes such as deflection or Y modulation and imaging modes such as back-scattered electron imaging (BEI) can provide clearer contrast, as shown in Figs 5.5 and 5.6. Heat aging of polymer fibers can cause cyclic trimers and oligomers to diffuse to the fiber 

The world textile industry is one of the largest consumers of dyestuffs. An understanding of the chemistry of textile fibers is necessary to select an appropriate dye from each of the several dye classes so that the textile product requirements for proper shade, fastness, and economics are achieved. The properties of some of the more commercially important natural and synthetic fibers are briefly discussed in this section. The natural fibers may be from plant sources (such as cotton and flax), animal sources (such as wool and silk), or chemically modified natural materials (such as rayon and acetate fibers). The synthetic fibers include nylon, polyester, acrylics, polyolefins, and spindex. The various types of fiber along with the type of dye needed are summarized in Table 8.2. 

Cotton. The cotton fiber is essentially cellulosic in nature and may be chemically described as poly (l,4-B-D-anh5nrdoglucopyranose), with the following repeat unit (about 3000 units)  

Fiber name Type/general classification Chemical constitution Ionic nature in dyebath 

Cotton, linen, and other vegetable fibers Natural hydrophilic Cellulose Anionic 

Viscose rayon Synthetic, hydrophilic Regenerated cellulose Anionic 

It is not surprising that words from this ancient craft still carry specialized meanings within the textile industry and have entered everyday parlance, quite often with very different meanings. Explanations are in order for some of the words used in the following pages. For example, as already indicated, spinning describes either the twisting of a bundle of essentially parallel short pieces of wool, cotton, or precut manufactured fibers into thread or 

The breaking tenacity or more commonly, tenacity, is the breaking strength of a fiber or a yarn expressed in force per unit denier, that is, in grams per denier, calculated from the denier of the original unstretched specimen. 

Typical force-elongation curves of some manufactured and natural staple fibers and textile-type manufactured filaments are shown in Figs. 21.1 and 21.2. 

The credit for using a spinnerette and forcing a solution through it for producing a fiber, 

By that year, 1910, the brothers Camille and Henry Dreyfus had discovered a practical method for producing cellulose acetate polymer and were making plastic film and toilet articles in Basel, Switzerland. During World War I, they built a plant in England to produce acetate dope for painting airplane wings to render them air-impervious. The success of the product led the U.S. government to invite the Dreyfus brothers to build a plant in the United States, which started commercial production in 1924. 

Birefringence, the difference between the refractive index parallel and perpendicular to the fiber axis, is an important quantitative measure of molecular orientation [18]. Birefringence is measured by either the Becke line (immersion) 

Fracture type Forms of fracture Polymer types Ref 

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Textile applications Textile bags Textile bleaching Textile cord Textile dyeing Textile fibers Textile finishes Textile finishing... 

The properties of textile fibers may be conveniently divided into three categories geometric, physical, and chemical, as shown in Table 4. 

In general, textile fibers should be optically opaque so that their refractive indexes need to be significantly different from those of their most common environments, namely, air and water. Luster and color are two optical properties that relate to a fiber s aesthetic quatity and consumer acceptance. 

Most textile fibers are hygroscopic at least to some extent, and therefore capable of absorbing moisture from the atmosphere, which is a direct reflection of chemical stmcture. Textile fibers vary from those that may be considered hydrophilic to those that are essentially hydrophobic (8—10). 

Fig. 3. Sorption isotherms of water on textile fibers at 25°C 0, wool x viscose D, silk O, cotton V, acetate A nylon.

Typical textile fibers have linear densities in the range of 0.33—1.66 tex (3 to 15 den). Fibers in the 0.33—0.66 tex (3—6 den) range are generally used in nonwoven materials as well as in woven and knitted fabrics for use in apparel. Coarser fibers are generally used in carpets, upholstery, and certain industrial textiles. A recent development in fiber technology is the category of microfibers, with linear densities <0.11 tex (1 den) and as low as 0.01 tex. These fibers, when properly spun into yams and subsequendy woven into fabrics, can produce textile fabrics that have excellent drape and softness properties as well as improved color clarity (16). 

A schematic stress-strain curve of an uncrimped, ideal textile fiber is shown in Figure 4. It is from curves such as these that the basic factors that define fiber mechanical properties are obtained. 

Fig. 4. Idealized stress-strain curves of an uncrimped textile fiber point 1 is the proportional limit, point 2 is the yield point, and point 3 is the break or...

The elasticity of a fiber describes its abiUty to return to original dimensions upon release of a deforming stress, and is quantitatively described by the stress or tenacity at the yield point. The final fiber quaUty factor is its toughness, which describes its abiUty to absorb work. Toughness may be quantitatively designated by the work required to mpture the fiber, which may be evaluated from the area under the total stress-strain curve. The usual textile unit for this property is mass pet unit linear density. The toughness index, defined as one-half the product of the stress and strain at break also in units of mass pet unit linear density, is frequentiy used as an approximation of the work required to mpture a fiber. The stress-strain curves of some typical textile fibers ate shown in Figure 5. 

Fig. 5. Stress—strain curves of some textile fibers (17). To convert N/mm to psi, multiply by 145.

An important aspect of the mechanical properties of fibers concerns their response to time dependent deformations. Fibers are frequently subjected to conditions of loading and unloading at various frequencies and strains, and it is important to know their response to these dynamic conditions. In this connection the fatigue properties of textile fibers are of particular importance, and have been studied extensively in cycHc tension (23). The results have been interpreted in terms of molecular processes. The mechanical and other properties of fibers have been reviewed extensively (20,24—27). 

With the exception of glass fiber, asbestos (qv), and the specialty metallic and ceramic fibers, textile fibers are a class of soHd organic polymers distinguishable from other polymers by their physical properties and characteristic geometric dimensions (see Glass Refractory fibers). The physical properties of textile fibers, and indeed of all materials, are a reflection of molecular stmcture and intermolecular organization. The abiUty of certain polymers to form fibers can be traced to several stmctural features at different levels of organization rather than to any one particular molecular property. 

R. Meredith, Mechanical Properties of Textile Fibers, Interscience Pubhshers, New York, 1956. 

W. E. Morton and J. W. S. Heade, Physical Properties of Textile Fibers, 2nd ed.. The Textile Institute and Butterworths Scientific Pubhcations,... 

Another property, used to compare the flammabiUty of textile fibers, is the limiting oxygen index (LOI). This measured quantity describes the minimum oxygen content (%) in nitrogen necessary to sustain candle-like burning. Values of LOI, considered a measure of the intrinsic flammabiUty of a fiber, are Hsted in Table 2 in order of decreasing flammabiUty. 

Table 2. Limiting Oxygen Index of Textile Fibers...

The elongation of a stretched fiber is best described as a combination of instantaneous extension and a time-dependent extension or creep. This viscoelastic behavior is common to many textile fibers, including acetate. Conversely, recovery of viscoelastic fibers is typically described as a combination of immediate elastic recovery, delayed recovery, and permanent set or secondary creep. The permanent set is the residual extension that is not recoverable. These three components of recovery for acetate are given in Table 1 (4). The elastic recovery of acetate fibers alone and in blends has also been reported (5). In textile processing strains of more than 10% are avoided in order to produce a fabric of acceptable dimensional or shape stabiUty. 

Fibrillated Fibers. Instead of extmding cellulose acetate into a continuous fiber, discrete, pulp-like agglomerates of fine, individual fibrils, called fibrets or fibrids, can be produced by rapid precipitation with an attenuating coagulation fluid. The individual fibers have diameters of 0.5 to 5.0 ]lni and lengths of 20 to 200 )Jm (Fig. 10). The surface area of the fibrillated fibers are about 20 m /g, about 60—80 times that of standard textile fibers. These materials are very hydrophilic an 85% moisture content has the appearance of a dry soHd (72). One appHcation is in a paper stmcture where their fine fiber size and branched stmcture allows mechanical entrapment of small particles. The fibers can also be loaded with particles to enhance some desired performance such as enhanced opacity for papers. When filled with metal particles it was suggested they be used as a radar screen in aerial warfare (73). 

E. R. KasweU, Textile Fibers, Yams, andFabrics, Reinhold Publishing Corp., New York, 1953, p. 57. 

Textile Fibers Products Identification A.ct, US. Public Eaw 85—897 U.S. Federal Trade Commission, Washington, D.C., effective Mar. 3,1960. 

Poly(ethylene terephthalate), the predominant commercial polyester, has been sold under trademark names including Dacron (Du Pont), Terylene (ICI), Eortrel (Wellman), Trevira (Hoechst-Celanese), and others (17). Other commercially produced homopolyester textile fiber compositions iaclude p oly (1,4-cyc1 oh exa n e- dim ethyl en e terephthalate) [24936-69-4] (Kodel II, Eastman), poly(butylene terephthalate) [26062-94-2] (PBT) (Trevira, Hoechst-Celanese), and poly(ethylene 4-oxyben2oate) [25248-22-0] (A-Tell, Unitika). Other polyester homopolymer fibers available for specialty uses iaclude polyglycoHde [26124-68-5] polypivalolactone [24937-51-7] and polylactide [26100-51-6],... 

In the late 1980s, new fully aromatic polyester fibers were iatroduced for use ia composites and stmctural materials (18,19). In general, these materials are thermotropic Hquid crystal polymers that are melt-processible to give fibers with tensile properties and temperature resistance considerably higher than conventional polyester textile fibers. Vectran (Hoechst-Celanese and Kuraray) is a thermotropic Hquid crystal aromatic copolyester fiber composed of -hydroxyben2oic acid [99-96-7] and 6-hydroxy-2-naphthoic acid. Other fully aromatic polyester fiber composites have been iatroduced under various tradenames (19). 

Most textile fibers are delustered with 0.1—3.0 wt % Ti02 to reduce the gHtter and plastic appearance. Many PET fibers also contain optical bTighteners (17). Through the use of soluble dyes or pigments, including photochromic pigments (19), a wide variety of producer-colored fibers and effects is available. 

Originally, the word rayon was appHed to any ceUulose-based man-made fiber, and therefore included the cellulose acetate fibers. However, the definition of rayon was clarified in 1951 and includes textiles fibers and filaments composed of regenerated cellulose and excludes acetate. In Europe the fibers are now generally known as viscose the term viscose rayon is used whenever confusion between the fiber and the cellulose xanthate solution (also called viscose) is possible. 

The first successhil attempt to make textile fibers from plant cellulose can be traced to George Audemars (1). In 1855 he dissolved the nitrated form of cellulose in ether and alcohol and discovered that fibers were formed as the dope was drawn into the air. These soft strong nitrocellulose fibers could be woven into fabrics but had a serious drawback they were explosive, nitrated cellulose being the basis of gun-cotton (see Cellulose esters, inorganic esters). 

Asahi Chemical Industries (ACl, Japan) are now the leading producers of cuprammonium rayon. In 1990 they made 28,000 t/yr of filament and spunbond nonwoven from cotton ceUulose (65). Their continuing success with a process which has suffered intense competition from the cheaper viscose and synthetic fibers owes much to their developments of high speed spinning technology and of efficient copper recovery systems. Bemberg SpA in Italy, the only other producer of cuprammonium textile fibers, was making about 2000 t of filament yam in 1990. 

The bulk properties of regenerated cellulose are the properties of Cellulose II which is created from Cellulose I by alkaline expansion of the crystal stmcture (97,101) (see Cellulose). The key textile fiber properties for the most important current varieties of regenerated cellulose are shown in Table 2. Fiber densities vary between 1.53 and 1.50. 

Since the early 1980s, the viscose-based staple fibers have, like the cuprammonium and viscose filament yams in the 1970s, ceased to be commodities. They have been repositioned from the low cost textile fibers that were used in a myriad of appUcations regardless of suitabUity, to premium priced fashion fibers dehvering comfort, texture, and attractive colors in ways hard to achieve with other synthetics. They are stiU widely used in blends with polyester and cotton to add value, where in the 1980s they would have been added to reduce costs. 

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