Synthetics fibers

Various synthetic fibers appear in clothing, upholstery, and industrial uses. They are better known by commercial names, that hide their source and composition. Quite often a blend of natural and synthetic fibers is offered. The first man-made fibers (that still are of major use) are essentially based on a modification of natural cellulose. Most common in use are rayon (viscose) and cellulose-acetate (called acetate). The oldest synthetic polymer in the textile industry is the polyamide (Nylon 6-6) developed in 1935. Currently there are many synthetic fibers, like the following  

Dacron or Terylene (a linear polyester based on teraphthalic acid). 

Saran is stable in water and withstands high temperatures. It is supplied as films or woven and it is extensively used for upholstery in household or transportation. It is found in interior clothing, suits, mgs, and tire reinforcement. Rayon suffers from high water absorbency and is frequently used as a blend with other fibers. An interesting product is found in PET (recovered from bottles) as a textile for interior and insulating clothing. Acetate is found as a blend in fine clothing and upholstery. Artificial fibers like Nylon and others can be used as a reinforcement to plastomers. A typical breakdown is shown in Table 6-2. 

The novel fibers serve as reinforcement for special performances like endurance at high temperatures and premium mechanical properties. They consist of aromatic polyesters and polyamides, polyimides and other high-performance polymers. Most distinguished are Kevlar , Nomex , Ekonol and PEEK . 

While many of the polymers used for synthetic fibers are identical to those in plastics, the two industries grew up separately, with completely different terminologies, testing procedures, and so on. Many of the requirements for fabrics are stated in nonquantitative terms such as hand and drape which are difficult to relate to normal physical property measurements, but which can be critical from the standpoint of consumer acceptance, and therefore the commercial success, of a fiber. 

A fiber is often defined as an object with a length-to-diameter ratio of at least 100. Synthetic fibers are spun (Section 19.12) in the form of continuous filaments, but may be chopped to much shorter staple, which is then twisted into thread before weaving. Natural fibers, with the exception of silk, are initially in staple form. The thickness of a fiber is most commonly expressed in terms of denier, which is the weight in grams of a 9000-m length of the fiber. Stresses and tensile strengths are reported in terms of tenacity, with units of grams/denier. 

The production of nylons and polyesters, which were first synthesized in the 1930s, has led to the development of man-made fibers. The complex sequence of catalytic reactions involved in both processes was originally based on 1930s technology but, as the reaction mechanisms came to be understood, catalysts were improved and, in some cases, new petrochemical feeds were introduced. 

Major fiber-making polymers are those of polyesters, polyamides (nylons), polyacrylics, and polyolefins. Polyesters and polyamides are produced by step polymerization reactions, while polyacrylics and polyolefins are synthesized by chain-addition polymerization. 

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The diazonium salt of 2-aminothiazole couples with 2-dimethylamino-4-phenylthiazole, giving the corresponding azo dye (194) (Scheme 123) used for dyeing synthetic fibers (404). 

The use of 2-aminothiazole derivatives as dyeing compounds is direct related to the development of synthetic fibers. Some typical examples are given in Table VI-14. The importance of these dyes lies in their performance on acetate fibers. They have excellent fastness to gas fumes, produce a bright blue shade, and have a high tinctorial strength. Their only disadvantage is their relatively low light fastness, which does limit their application. 

Pressure-sensitive copying paper containing 431 was recently patented (1650). 2-Thiazolyldiazonium chloride enters in the composition of synthetic fibers with ion-exchange properties (1551). 

The synthetic fiber industry as we know it began m 1928 when E I Du Pont de Nemours Company lured Professor Wallace H Carothers from Harvard University to direct their research department In a few years Carothers and his associates had pro duced nylon the first synthetic fiber and neoprene a rubber substitute Synthetic fibers and elastomers are both products of important contemporary industries with an economic influence far beyond anything imaginable m the middle 1920s... 

Synthetases Synthetic fatly acids Synthetic fiber blends Synthetic fibers... 

Control of relative humidity is needed to maintain the strength, pHabiUty, and moisture regain of hygroscopic materials such as textiles and paper. Humidity control may also be required in some appHcations to reduce the effect of static electricity. Temperature and/or relative humidity may also have to be controlled in order to regulate the rate of chemical or biochemical reactions, such as the drying of varnishes, the appHcation of sugar coatings, the preparation of synthetic fibers and other chemical compounds, or the fermentation of yeast. 

Chemical Manufacturing. Chemical manufacturing accounts for over 50% of all U.S. caustic soda demand. It is used primarily for pH control, neutralization, off-gas scmbbing, and as a catalyst. About 50% of the total demand in this category, or approximately 25% of overall U.S. consumption, is used in the manufacture of organic intermediates, polymers, and end products. The majority of caustic soda required here is for the production of propylene oxide, polycarbonate resin, epoxies, synthetic fibers, and surface-active agents (6). 

Essentially all the ammonium sulfate fertilizer used in the United States is by-product material. By-product from the acid scmbbing of coke oven gas is one source. A larger source is as by-product ammonium sulfate solution from the production of caprolactam (qv) and acrylonitrile, (qv) which are synthetic fiber intermediates. A third but lesser source is from the ammoniation of spent sulfuric acid from other processes. In the recovery of by-product crystals from each of these sources, the crystallization usually is carried out in steam-heated sa turator—crystallizers. Characteristically, crystallizer product is of a particle size about 90% finer than 16 mesh (ca 1 mm dia), which is too small for satisfactory dry blending with granular fertilizer materials. Crystals of this size are suitable, however, as a feed material to mixed fertilizer granulation plants, and this is the main fertilizer outlet for by-product ammonium sulfate. 

Table 2. Worldwide Synthetic Fiber Production by Fiber, 10 t...

In general, the geometric properties of the natural fibers are highly variable from fiber to fiber, both within a given lot and among lots of the same fiber type. In the synthetic fibers, the geometric properties are extremely uniform in view of the production control possible in a chemical plant but not in an agricultural product. 

The physical properties of these fibers are compared with those of natural fibers and other synthetic fibers in Table 1. Additional property data may be found in compilations of the properties of natural and synthetic fibers (1). Apart from the polyolefins, acryhcs and nylon fibers are the lightest weight fibers on the market. Modacryhcs are considerably more dense than acryhcs, with a density about the same as wool and polyester. 

The mechanical properties of acryUc and modacryUc fibers are retained very well under wet conditions. This makes these fibers well suited to the stresses of textile processing. Shape retention and maintenance of original bulk in home laundering cycles are also good. Typical stress—strain curves for acryhc and modacryUc fibers are compared with wool, cotton, and the other synthetic fibers in Figure 2. 

Visual and Manual Tests. Synthetic fibers are generally mixed with other fibers to achieve a balance of properties. Acryhc staple may be blended with wool, cotton, polyester, rayon, and other synthetic fibers. Therefore, as a preliminary step, the yam or fabric must be separated into its constituent fibers. This immediately estabUshes whether the fiber is a continuous filament or staple product. Staple length, brightness, and breaking strength wet and dry are all usehil tests that can be done in a cursory examination. A more critical identification can be made by a set of simple manual procedures based on burning, staining, solubiUty, density deterrnination, and microscopical examination. 

General schemes for the identification of natural and synthetic fibers have been estabhshed by the Textile Institute and by the American Association of Textile Chemists and Colorists (8). A comprehensive treatment of burning, solvent, staining, microscopy, and density techniques has been given (9) and a general discussion of procedures for identifyiag synthetic fibers has been presented (10). 

World Synthetic Fibers 1991 —2001, Tecnon UK, Ltd., Plantation Wharf, London, Aug. 1992. 

Cellulose acetate, the second oldest synthetic fiber, is an important factor in the textile and tobacco industries 731,000 metric tons were produced worldwide in 1991 (Fig. 11) (74). Acetate belongs to the group of less expensive fibers triacetate is slightly more expensive. An annual listing of worldwide fiber producers, locations, and fiber types is pubHshed by the Fiber Economics Bureau, Inc. (74). 

Physical Properties. Table 1 (2) shows that olefin fibers differ from other synthetic fibers in two important respects (/) olefin fibers have very low moisture absorption and thus excellent stain resistance and almost equal wet and dry properties, and (2) the low density of olefin fibers allows a much lighter weight product at a specified size or coverage. Thus one kilogram of polypropylene fiber can produce a fabric, carpet, etc, with much more fiber per unit area than a kilogram of most other fibers. 

Fig. 17. Distribution of U.S. synthetic fiber consumption A, acryUc I, olefin +, nylon and aramid A, polyester (71,72).

However, because of the low melting poiats and poor hydrolytic stabiUty of polyesters from available iatermediates, Carothers shifted his attention to linear ahphatic polyamides and created nylon as the first commercial synthetic fiber. It was nearly 10 years before. R. Whinfield and J. T. Dickson were to discover the merits of poly(ethylene terephthalate) [25038-59-9] (PET) made from aromatic terephthaUc acid [100-21-0] (TA) and ethylene glycol [107-21-1] (2G). 

Commercial production of PVA fiber was thus started in Japan, at as early a period as that for nylon. However, compared with various other synthetic fibers which appeared after that period, the properties of which have continuously been improved, PVA fiber is not very well suited for clothing and interior uses because of its characteristic properties. The fiber, however, is widely used in the world because of unique features such as high affinity for water due to the —OH groups present in PVA, excellent mechanical properties because of high crystallinity, and high resistance to chemicals including alkah and natural conditions. 

Moisture Absorbency. PVA fiber is more hygroscopic than any other synthetic fiber. The hygroscopicity varies depending on how the fiber is processed after spinning, ie, in heat-drawing, he at-treatment, acetalization, and the like. 

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