Fibers and Fibrous Materials

The main constituent of all fibers of vegetable origin (see Table 88) is, almost exclusively, cellulose, a polymeric carbohydrate (see Textbox 53). Vegetable fibers are resistant to alkalies and to most organic acids but are destroyed by strong mineral acids. 

Vegetable Cotton, linen Fine fibers Cellulose, a polymeric carbohydrate 

Animal Hair, wooi Staple fibers Keratin, a protein 

Mineral Asbestos Fibers Fibrous mineral silicates 

The first fibers used by humans were probably those that occur naturally as tissues or excretions of either vegetables or animals (see Table 87). At much later times, after metals had been discovered, humans also learned to manufacture - from some of the ductile metals, mainly gold, silver, and their alloys - thin filaments (not fibers, however), which have since been used to decorate textile fabrics. It was only during the twentieth century, after synthetic plastics were discovered, that it became possible to make artificial human made fibers. The great majority of the natural fibers, such as cotton and wool, occur as staple fibers, short fibers whose length is measured in centimeters. Silk is different from all other natural fibers in that it occurs as extremely long and continuous filaments several hundred meters long. 

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Nature is full of fibers and fibrous materials, and it has been consistently recognized that the science and technology of fibers were learnt from silkworms and spiders, since their fiber-producing processes are good examples of biosynthetic and biospinning techniques in which they convert nonfiber foods by enzymes into proteins in the body and then spin fibers as a cocoon or net. 

There is a relationship that accommodates the wide range of fiber sizes and is independent of the composition or constitution of the fiber or fibrous material. The aspect ratio, or the relationship of the length to the thickness of the particle (length/thickness), can be calculated or estimated with relative ease. 

Rauch, H. W., Jr., W. H. Sutton, and L. R. McCreight (1968). Fibers and Fibrous Composite Materials. Academic Press, New York. 

Many important biological substances do not form crystals. Among these are most membrane proteins and fibrous materials like collagen, DNA, filamentous viruses, and muscle fibers. Some membrane proteins can be crystallized in matrices of lipid and studied by X-ray diffraction (Chapter 3, Section III.D), or they can be incorporated into lipid films (which are in essence two-dimensional crystals) and studied by electron diffraction. I will discuss electron diffraction later in this chapter. Here I will examine diffraction by fibers. 

It has been shown that even extremely small concentrations of additives can make plastics conductive if they are in the form of conductive fibers with length to diameter (LID) ratio of 100 or more. The striking difference between the use of chunky fragments and fibrous materials in their effect on conductivity can be seen from the diagram in Figure 5.13. 

Multifunctional Materials. Multifunctional property improvement by binding of specific polymers to fibers and fibrous products has been extensively investigated and reviewed (81). With poly(ethylene glycol) as the bound polymer, functional and aesthetic property improvements include thermal comfort, liquid absorbency/repellancy, increased wear life, soil release, resistance to static charge, antimicrobial activity, and resiliency. Numerous applications such as sportswear/ski wear, protective clothing for health care workers, durable and nondurable hygienic items, work uniforms, and space suits are being commercialized and evaluated. 

Feeder Operation It is common to sequence the addition of SPS ingredients to the compounding extruder. The pellets, crumb, oil, and powders are added at the feed funnel of the extruder. Glass fiber and fibrous fillers are fed through the side of the extruder barrel at the point the resin is melted and well mixed with the other ingredients that were introduced at the feed funnel. This is done to avoid excessive attrition of the fibrous additives. The amount of material that can be added to the extruder is dependent on the torque capabilities of the extruder. 

The twentieth century left a lasting impression of the First World War, during which toxic gases were used for the first time. This was the reason that after 1914, the further history of the development of filtration materials was cormected with absorbers of toxic substances manufactured with the use of charcoal and fibrous materials. The next discovery, which changed the approach to the designing of filtration materials, was done in 1930, Hansen, in his filter applied a mixture of fibers and resin as filtration materials. This caused an electrostatic field being created inside the material. The action of electrostatic forces on dust particles significantly increases the filtration efficiency of the materials manufactured. 

To understand the heat and moisture flow characteristics of textile fabrics, many mathematical models have been propounded. Matty computational tools like Computational Fluid Dynamics (CFD), artificial neural networks, fuzzy logic and many more are also being used to understand the complex relationships between the clothing parameters and the perception of comfort. This chapter deals with the studies on heat and mass transfer properties of textile assemblies. The phenomena covered here are diy steady state heat transfer, transient heat transfer, moisture vapor and liquid moisture transfer and coupled heat and moisture transfer properties of fibers, fiber bundles, fibrous materials and other textile stmctures. The processes involved in each and the woik done on modeling and simulation of the transfer processes till date, from the point of view of clothing comfort have been discussed. 

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182). 

Fibers are used ia the manufacture of a wide range of products that can generically be referred to as fibrous materials. The properties of such materials are dependent on the properties of the fibers themselves and on the geometric arrangement of the component fibers ia the stmcture. 

This brief overview of the types of fibrous materials is intended to indicate the broad range of materials that can be produced from fibers. Since the properties of fibrous materials depend both on the properties of the fibers themselves and on the spatial arrangement of the fibers in the assembly, a given type of fiber may be used in many different end products, and similarly a given end product can be produced from different fiber types. 

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

Physical testing appHcations and methods for fibrous materials are reviewed in the Hterature (101—103) and are generally appHcable to polyester fibers. Microscopic analyses by optical or scanning electron microscopy are useful for evaluating fiber parameters including size, shape, uniformity, and surface characteristics. Computerized image analysis is often used to quantify and evaluate these parameters for quaUty control. 

Fibrous ndFoa.medMa.teria.ls, Most sound-absorbiag materials are fibrous or porous and are easily penetrated by sound waves. Air particles excited by sound energy move rapidly to and fro within the material and mb against the fibers or porous material. The frictional forces developed dissipate some of the sound energy by converting it iato heat. 

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