Fibers formation

It must be emphasized that after the solvent is removed, the polymer crystallizes. Thus the aromatic polyamide fibers, while existing in liquid crystal mesophases during preparation, are highly crystalline when fuUy formed. Again, because of the lack of chain folds and other imperfections, the fibers have higher moduli and higher strength. 

From the relation L=f(vij) it is obvious that the spinnability is governed by two processes, namely the cohesive break (or the swell effect) and the melt break (capillary break, melt fracture). According to Section 11.3.1, a certain amount of elastic energy can be stored in all viscoelastic fluids. This phenomenon leads, among others, to the Barus effect. 

Fi(/ure 12-4. Length of fiber L as a function of the fiber production rate o and viscosity fj in spinning solutions of cellulose acetate at different concentrations in an acetone-water ntixiuie (S5 15). L at the maximum is the spinnability, (From A. Ziabicki, according to data from Y. Oshima, H. Macda, and T. Kawai.) 

This results in a periodic swelling and breaking of the fiber. Sometimes this phenomenon is made use of commercially, since under carefully controlled conditions, periodic swelling leads to a fiber of decorative appearance and high bulk. 

Dye staining gives the microfibril a striated appearance under the electron microscope. 

Lysine residues predominate around the gaps, causing glycan attachment and polypeptide cross-linking. 

Site of fiber interactions with non-fibrous collagens 

The tropocollagen [5- and y-chains in Fig. 4.1 are respectively twice and three-times the size of the a-chain. Indeed, their amino acid composition is virtually identical to the a-chain in Fig. 4.1, except for the appearance of derivatives of lysine and hydroxylysine, mainly lysyl hydroxyl-norleucine and pyridinoline. They increase in amount with age of the organism. 

Cross-linking contributes to tissue strength and limits the need for fiber replacement, but it also inhibits repair following a mechanical injury or infection (Sect. 8.1.3.). Lysyl oxidase catalysis is self-limiting to avoid excessive cross-linking. The oxidation rate of lysine amine residues is limited to approximately 100 catalytic turnovers per enzyme molecule because ammonia and other reaction by-products inactivate it irreversibly. 

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Fig. 7. Fiber formation by MCVD, where V represents the O2—H2 flame, showing (a), tube setup (b), deposition and (c), coUapse.

Mechanical Properties. Polyester fibers are formed by melt spinning generally followed by hot drawing and heat setting to the final fiber form. The molecular orientation and crystalline fine stmcture developed depend on key process parameters in all fiber formation steps and are critical to the end use appHcation of the fibers. 

Incorporation of Flame Retardants in Fiber. Flame retardants suitable for cotton are also suitable for rayon. A much better product is obtained by incorporating flame retardants in the viscose dope before fiber formation. The principal classes of flame retardants used in viscose dope are tabulated aimuaHy (111). 

The mode of action has not yet been elucidated but the manufacturer states that it probably behaves like the herbicide triflurolin and its congeners. These materials inhibit cell division by binding to tubuHn thereby internipting micro-tubule development. This, in turn, stops spindle fiber formation essential to mitosis and cell division. Experiments with C-labeled Prime+ show that it is acutely toxic to fish with estimated LC q (96 h) of less than 100 ppb for rainbow trout and bluegiU. sunfish. However, channel catfish did not exhibit any toxic response at the maximum attainable water concentration (10). 

C. Characteristically, these nematic melts show the persistence of orientational order under the influence of elongational flow fields which result in low melt viscosities under typical fiber formation conditions even at high molecular weights. 

Materials. Supercritical fluids offer many opportunities in materials processing, such as crystallization, recrystallization, comminution, fiber formation, blend formation, and microceUular (foam) formation. 

Manufactured fibers produced from natural organic polymers are either regenerated or derivative. A regenerated fiber is one which is formed when a natural polymer or its chemical derivative is dissolved and extmded as a continuous filament, and the chemical nature of the natural polymer is either retained or regenerated after the fiber-formation process. A derivative fiber is one which is formed when a chemical derivative of the natural polymer is prepared, dissolved, and extmded as a continuous filament, and the chemical nature of the derivative is retained after the fiber-formation process. 

Chry sotile is a hydrated magnesium siHcate and its stoicliiometric chemical composition may be given as AIg2Si20 (0H)4 [12001 -29-5]. However, the geothermal processes wliich ield the chry sotile fiber formations usually involve the co-deposition of v arious other minerals. Tliese mineral contaminants comprise brucite [1317-43-7] (AIg(OH)2), magnetite [1309-38-2] (Fe O, calcite [13397-26-7] (CaCO ), dolomite [16389-88-1] (AIg,CaC02),... 

In contrast to chrysotile fibers, the atomic crystal stmcture of amphiboles does not inherentiy lead to fiber formation. The formation of asbestiform amphiboles must result from multiple nucleation and specific growth conditions. Also, whereas the difference between asbestiform and massive amphibole minerals is obvious on the macroscopic scale, the crystalline stmctures of the two varieties do not exhibit substantial differences. Nonfibrous amphiboles also exhibit preferential cleavage directions, yielding fiber-shaped fragments. 

More than 95% of current carbon fiber production for advanced composite appHcations is based on the thermal conversion of polyacrylonitrile (PAN) or pitch precursors to carbon or graphite fibers. Generally, the conversion of PAN or pitch precursor to carbon fiber involves similar process steps fiber formation, ie, spinning, stabilization to thermoset the fiber, carbonization—graphitization, surface treatment, and sizing. Schematic process flow diagrams are shown in Eigure 4. However, specific process details differ. 

The mesophase pitch is then extmded and melt spun through spinnerettes into fibers. The flow pattern of the mesophase during fiber formation has a strong influence on the morphology of the fiber (52—54) and can result in fibers with radial, onion-skin, or random microstmctures. Commercially available PBCFs have a round cross section, but this can be easily modified by changing the cross section of the spinnerette holes. Multilobal and C-shaped fibers have been produced with exceptional mechanical properties (55). 

Peebles, L. H., Carbon fibers from acrylic precursors. In Carbon Fibers Formation, Structure, and Properties. CRC Press, Boca Raton, FL, 1995, pp. 7 26. 

With respect to the formation of unwanted polyaromatic hydrocarbons in the pyrolytic process, it has been shown that conditions can be maintained where such fonuation is negligible according to EPA and OSHA standards. As production rates are increased, it will be incumbent on any manufacturer to maintain a set of operating parameters which produce an environmentally-benign product however, current information regarding the process for fiber formation reveals no barriers to accomplishing this. 

Faser-asbest, m. fibrous asbestos, -asche, /. fiber ash. -bildung, /. fiber formation, fibra-tion. -blende, /. fibrous sphalerite. Faserchen, n. little fiber, fibril, filament. Faserfarbung, /. coloration of the fiber, faserfdrmig, a. fibrous, filiform. 

As recognized by others in the case of TLCP blends, it may be detrimental to fiber formation if the matrix and TLCP are too compatible [12,13,49-51]. This can... 

In addition, it was found that the blends with highly fibrillar structure exhibited a significantly lowered viscosity. Increased shear rate caused slight changes in the blend morphology but did not enhance the fiber formation. Thus, in addition to shear, elongational forces are needed to achieve a well-fibrillated blend structure and significant mechanical reinforcement. 

Fibers in which the basic chemical units have been formed by chemical synthesis, followed by fiber formation, are called synthetic fibers. Examples include nylon, carbon, boron fibers, organic fibers, ceramic fibers, and metallic fibers. Among all commercially available fibers, Kevlar fibers exhibit high strength and modulus. (Kevlar is a DuPont trademark for poly [p-phenylene diamine terephthalamide].) It is an aromatic polyamide (aramid) in which at least 85% of the... 

Henrici-Olive, G. and Olive, S. The Chemistry of Carbon Fiber Formation from Polyacrylonitrile. Vol. 51, pp. 1—60. 

Amine salts of a-sulfonated fatty acids and esters are also used as antistatic agents. Mixtures of alkyl a-sulfo fatty acid ester diethanolamine salts and hexa-decyl stearate or butyl stearate are coated onto nylon yarn after fiber formation and before stretching [97]. Polypropylene can be made antistatic with an amine salt of a-sulfolauric acid [C10H21CH(SO3Na)COO +NH(CH2CH(OH) CH3)3] [98]. 

Elastin is a heavily crosslinked biopolymer that is formed in a process named elastogenesis. In this section, the role of elastin and the different steps of elastin production will be described, starting with transcription of the genetic code and processing of the primary transcript, followed by translation into the elastin precursor protein and its transport to the extracellular matrix. Finally, the crosslinking and fiber formation, which result in the transition from tropoelastin to elastin, are described. 

Research into elastin, its properties, and the fiber formation was for a considerable period of time hindered due to its insolubihty. However, discovery of the soluble tropoelastin precursor made new investigations possible. The tropoelastin protein can be isolated from copper-deficient animals. However, this is a very animal-unfriendly and low yielding process [2]. Therefore, it is preferred to obtain tropoelastin from overexpression in microbial hosts such as Escherichia coli (E. coli). Most studies are thus based on tropoelastin obtained via bacterial production. 

The same ceUs that secrete collagen also secrete fi-bronectin, a large glycoprotein present on cell surfaces, in the extracellular matrix, and in blood (see below). Fi-bronectin binds to aggregating precollagen fibers and alters the kinetics of fiber formation in the pericellular matrix. Associated with fibronectin and procollagen in... 

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