Important Fibers

A study of the fiber industry is not complete without some knowledge of the characteristics of individual fibers. Since each is so different it is difficult to generalize or compare directly. This section presents a summary of each important fiber, including pertinent information on their manufacture, properties, uses, and current economics in a brief, informal and concise manner. 

Fewer processing steps, cheaper than wool 

Absorbs water but dries easily. If preshrunk, it is stable to washing and ironing more than other fibers. 

Hydrophilic—cool and comfortable. Comfort never matched by synthetics. Used especially in towels and drying cloths. Disadvantages creases easily, requiring frequent ironing  

Good warmth due to natural crimp (many folds and waves) which retains air, therefore a good insulator 

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Vegetable fibers are classified according to their source ia plants as follows (/) the bast or stem fibers, which form the fibrous bundles ia the inner bark (phloem or bast) of the plant stems, are often referred to as soft fibers for textile use (2) the leaf fibers, which mn lengthwise through the leaves of monocotyledonous plants, are also referred to as hard fibers and (J) the seed-hair fibers, the source of cotton (qv), are the most important vegetable fiber. There are over 250,000 species of higher plants however, only a very limited number of species have been exploited for commercial uses (less than 0.1%). The commercially important fibers are given ia Table 1 (1,2). 

Wool belongs to a family of proteins, the keratins, that also includes hair and other types of animal protective tissues such as horn, nails, feathers, and the outer skin layers. The relative importance of wool as a textile fiber has declined over the decades as synthetic fibers have increa singly been used in textile consumption. Wool is still an important fiber in the middle and upper price ranges of the textile market. It is also an extremely important export for several nations, notably AustraUa, New Zealand, South Africa, and Argentina and commands a price premium over most other fibers because of its outstanding natural properties of soft handle (the feel of the fabric), moisture absorption abiUties (and hence comfort), and superior drape (the way the fabric hangs) (see Fibers Textiles). Table 2 shows wool production and sheep numbers in the world s principal wool-producing countries. 

Utilized in spin dyeing, P.Gr.7 lends color to all types of commercially important fibers. The products demonstrate excellent lightfastness and weatherfastness. Used in polyacrylonitrile, for instance, P.Gr.7 satisfies the stringent requirements for use in outdoor textiles such as canvasses. Its textile fastness properties are almost, if not completely satisfactory. This textiles field is another area in which Copper Phthalocyanine Blue types are more than twice as strong as P.Gr.7. 

The important fiber rayon is simply regenerated cellulose from wood pulp that is in a form more easily spun into fibers. Cellophane film is regenerated cellulose made into film. One method of regeneration is formation of xanthate groups from selected hydroxy groups of cellulose, followed by hydrolysis back to hydroxy groups. 

Referring back to Fig. 16.1, we see that the value of U.S. shipments for cellulosic and noncellulosic fibers, though quite small compared to plastics, is still a big industry. While Plastics Materials and Resins (NAICS 325211) in 1998 was 44.9 billion, Noncellulosic Fibers (NAICS 325222) was 10.5 billion and Cellulosic Fibers (NAICS 325221) was 1.5 billion. These two fibers together have a 12.0 billion value, which is 3% of Chemical Manufacturing. We must also remember that many of these fibers are sold outside the chemical industry, such as in Textile Mill Products, Apparel, and Furniture, all large segments of the economy. The importance of fibers is obvious. In 1920 U.S. per capita use was 30 Ib/yr, whereas in 1990 it was 66 Ib/yr. From 1920 to 1970 the most important fiber by far was cotton. 

As first described in Section 1.4.2, there are a number of ways of further classifying fiber-matrix composites, such as according to the fiber and matrix type—for example, glass-fiber-reinforced polymer composites (GFRP) or by fiber orientation. In this section, we utilize all of these combinations to describe the mechanical properties of some important fiber-reinforced composites. Again, not all possible combinations are covered, but the principles involved are applicable to most fiber-reinforced composites. We begin with some theoretical aspects of strength and modulus in composites. 

Wet Classification Method. A second industrially important fiber-length evaluation technique is the Bauer-McNett (BMN) classification. 

This subcosmopolitan family produces one economically important fiber, jute, as well as some timber and local medicinals. 

Several fiber types have been mentioned so far, and several other types have been neglected that have been worked on over the past few years. Some of those not discussed may become important fibers for reinforcement in the years ahead. To date though, they have not been available in sufficient quantity for thorough evaluation in composite specimens. Included in this group are boron carbide, spinel, polycrystalline alumina and silica, titanium diboride, and miscellaneous silicides and intermetallics. Ten years from now as we look back on the 70s we no doubt will have an entirely different view of some of these materials. 

The most important fibers for printing are cellulosics (70%) and polyester (20%). All others account for less than 10%. 

The most important fiber blends consist of polyester and cellulose fibers or wool. Of the worldwide consumption of PES fibers, ca. 45 % is used in blends with cellulose fibers. In polyester-cellulose blends the cellulose component is usually cotton or viscose staple fibers The preferred mixing ratio is PES CEL 67 33 and, for textiles worn close to the skin, 50 50 to 20 80. 

The other important fiber in this category, which also was first produced commercially in the United States, is Kevlar , introduced in... 

Because most dyeings are applied from water solutions or dispersions, the effect of water absorption by the fiber is an important criterion. Table 13.3 shows the hydropho-bic/hydrophilic characteristics of the important fibers. The cellulosic and natural fibers are the most hydrophilic, and polyolefin is the most hydrophobic. 

In summary, cotton s future is positive. Cotton use should benefit from consumer demand stemming from favorable economic growth prospects and because of research. On the production side, global output should continue to provide an adequate supply for mill demand. Finally, cotton, one of the most important textile fibers and one of the world s important oilseed crops, should continue to be recognized as a significant commodity in world trade and the consumption of this important fiber, food, and feed crop will continue to grow but at a slower rate than synthetic fibers. 

The density of fibers is a very important attribute. We mentioned above the use of linear density or mass per unit length. That term is really suitable for giving m idea of the fiber size. Bulk density or mass per unit volume tells us how heavy a material is. Bulk density values of some important fibers are given in Table 2.2. The reader can easily verify that if we divide the linear density of a fiber by its... 

Although aramid fiber is by far the most successful fiber made via the liquid crystal route, there are some other important fibers that have been made by this process. For example, poly(p-phenylene benzobisthiazole) (PBT) (Wolfe et al, 1981a, 1981b) is synthesized from terephthalic acid and 2,5-diamino-l,4-ben-zenedithiol dihydrochloride (DBD). The DBD is first dissolved in poly-phosphoric acid (PPA), followed by dehydrochlorination. Terephthalic acid and more PPA are then added and the mixture is heated to 160°C to make a solution. The solution is heated to 180 C and reacted for 18 hours to obtain the... 

It is important to recognize that asbestos is not a single substance, but is the generic name for a family of six related poly silicate fibrous minerals of which one (chrysotile) belongs to the serpentine family and five (actinolite, amosite, anthophyllite, crocidolite, and tremolite) belong to the amphibole family. These minerals differ from each other in physical and chemical properties, and each mineral can exist in a wide range of fiber sizes. These differences between fiber type and, more importantly, fiber size (length and diameter) are believed to be important determinants of the health risks posed by asbestos. 

The most important fiber-reinforced inorganic-based product i,s asbestos cement, which has been used in the building indu,stry since 1900, Asbestos nbers (normally chrysotile) are bonded by Portland cement and the mixture sets to a fiber-rein forced material with 10 to 20% asbestos, which has excellent properties (Eternit , Fulgurit etc,)... 

Many important fibers, including cotton and wool, are naturally occurring polymers. The first commercially successful synthetic polymers were made not by polymerization reactions but through the chemical regeneration of the natural polymer cellulose, a condensation polymer of the sugar glucose that is made by plants ... 

Table 23.1 summarizes the structures, properties, and uses of some important fibers. 

Although natural fibers are usually classified according to their origin as animal or vegetable, chemists generally think of them from the viewpoint of their chemical nature as protein or cellulosic. The mineral kingdom also produces an important fiber—asbestos —which has had Incited use in the textile field because of processing difficulties. 

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