Spinning of fibers

Polymer melt spinning is one of the major processes for the manufacture of synthetic fibers. Typically, a polymer melt is extruded vertically downward through a spinneret or die, which may have hundreds of openings. The resulting filaments are simultaneously cooled by crossflow air and are stretched by the action of rollers. On solidification, the yam is wound onto a bobbin. Different aspects of this operation have been described in the literature.(, 59-63) When the fiber-spinning process is used as an extensional viscometer, the setup is simplified and only a single filament of circular cross section is employed. This is shown schematically in Fig 6. Also, the operation is run in an isothermal manner by spinning into an isothermal oven. 

Data on extensional stresses in fiber melt spinning, and their constitutive modeling for both isothermal and nonisothermal fiber spinning, can be found in the several books referred to earlier. Further modeling elforts are discussed by Denn.(66) However, it is fair to say that no totally acceptable rheological model has so far been found to quantitatively explain viscoelastic fiber-spinning results. The question of rheological constitutive equations is examined briefly in Section 7. 

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Sundaram RM, Koziol KKK, Windle AH. Continuous direct spinning of fibers of single-walled carbon nanotubes with metallic chirality. AdvMater. 2011 Nov 16 23(43) 5064-8. 

Figure 17.3 Spinning of fibers for use in earpets. (Courtesy of Du Pont)...

The synthesis of intermediary inorganic sols or polymers in solution whose rheological properties may be attractive for the film deposition techniques such as spin coating or the spinning of fibers. 

Polyvinyl Halides. Chlorinated Polyvinyl Chloride It was produced in Germany up to three decades ago, but this was primarily a 1,1-disubstituted product of increased solubility for dry-spinning of fibers. Goodrich has developed a light-activated suspension chlorination process which produces 1,2-dichlorinated structures of increased hot strength, thermal stability, and flame resistance. 

Capillary Viscometer. The end products from the liquid mixtures are usually obtained by extruding the liquid mass through narrow tubes or slits (e.g., spinning of fibers, injection molding, or film extrusion). Therefore, the pressure flow through a capillary is of technological interest. Hence, we analyzed the flow of a liquid mixture through a capillary with circular cross-section and compared the results of theory and measurement. 

A considerable amount of subsequent research and process development has been carried out to produce silicon carbide with a reduced level of excess carbon via processes that allow more facile cross-linking.2 -32 Several hundred papers and patents on this topic exist in the literature, and only a few examples will be mentioned here. One process development involves the slurry spinning of fibers in place of melt spinning.33 In this process, silicon carbide powder, made by a conventional industrial process, is dispersed in a solution of carbosilanes in toluene. The syrupy paste is spun into fibers and then pyrolyzed to silicon carbide. These fibers are reported to be stable at 1,500 °C for 120 hours. 

As an example using NMMO solution, the spinning of fibers consisting of blends of cellulose with cationic starch was investigated for the purpose of improving moisture absorbability, dyeability, and enzymatic degradability compared with standard Lyocell fibers [69]. 

Fig. 12.14 Effect of the method of measurement on the value of D/Do for HDPE. Curve 1, frozen extrudates Curve 2, extrudates annealed at 160°C in hot silicon oil Curve 3, photographs of extrudates emerging from capillary Curve 4, photographs of extrudates in hot silicon oil. [Reprinted by permission from J. L. White and J. F. Roman, Extrudate Swell During the Melt Spinning of Fibers-Influence of Rheological Properties and Take-up Force, J. Appl. Polym. Sci., 20, 1005 (1976).]...

J. L. White and J. F. Roman, Extrudate Swell During the Melt Spinning of Fibers—Influence of Rheological Properties and Take-up Force, J. Appl. Polym. Sci., 20, 1005 (1976). 

Cotton bolls dehisce at maturity, leaving the fibers fully exposed to air and sunlight. The water content of the fiber decreases rapidly, the cytoplasm dries against the inner surface of the wall, and a large lumen is left where the central vacuole was once located. The formerly tube-shaped cell collapses and assumes a twisted ribbon conformation with a kidney-like cross-sectional pattern. These twists, or convolutions, permit the spinning of fiber cells into yarns. 

The spinning of fibers from the nematic liquid crystalline state may at least in principle result in fibrous structures exhibiting nearly perfect molecular orientation. Imperfections such as chain ends should then be randomly distributed. A large amount of work has been performed in recent years on semicommercialized LCP s and also on more research based LCP s (13-161. 

FIGURE 1.37 Motor-driven laboratory scale fa- wet spinning of fibers. 

FIGURE 1.41 Large-scale setup for dry spinning of fibers. 

Phase separation spinning was reported in detail by Zwick [134]. This method allows spinning of fibers at winding speeds of 10-1000 m/min from solutions of polymer contents of 10-25%, with the use of modified melt-spinning equipment. T o realize phase separation, the concentration of the solution has to be chosen so that, on the way from the spinneret to the winder, and at a temperature between that of the spinneret and room temperature, the thin streams of polymer undergo phase separation into a concentrated gel, or pure polymer phase, and a solvent phase. 

The Russian Fenilon process utilizes low-salt content MPDI solutions [89]. Most of the hydrochloric acid generated during the polymerization process is removed by treatment with ammonia. The resulting insoluble ammonium chloride is filtered from the polymerization solution. Residual HCl is likely neutralized with an organic base. The neutralized solution is suitable for wet spinning of fibers. 

Molecular theories of mesomorphic polymers may serve to give a better insight into the mechanisms involved in the formation of ordered phases in macromolecular liquids. The importance of parameters such as chain length, chain flexibility... can be explored and the results used in synthesis of new systems with well-defined characteristics. Studies of the influence of solvents on the mesomorphic phase transition and the possibility of ordering by external fields (electric, magnetic, flow) are problems of technological in-ter>est in the spinning of fibers and in the formation of new polymer blends. 

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