Fiber melt-spun

Properties. As prepared, the polymer is not soluble in any known solvents below 200°C and has limited solubiUty in selected aromatics, halogenated aromatics, and heterocycHc Hquids above this temperature. The properties of Ryton staple fibers are in the range of most textile fibers and not in the range of the high tenacity or high modulus fibers such as the aramids. The density of the fiber is 1.37 g/cm which is about the same as polyester. However, its melting temperature of 285°C is intermediate between most common melt spun fibers (230—260°C) and Vectran thermotropic fiber (330°C). PPS fibers have a 7 of 83°C and a crystallinity of about 60%. 

HoUow-fiber fabrication methods can be divided into two classes (61). The most common is solution spinning, in which a 20—30% polymer solution is extmded and precipitated into a bath of a nonsolvent, generally water. Solution spinning allows fibers with the asymmetric Loeb-Soufirajan stmcture to be made. An alternative technique is melt spinning, in which a hot polymer melt is extmded from an appropriate die and is then cooled and sohdified in air or a quench tank. Melt-spun fibers are usually relatively dense and have lower fluxes than solution-spun fibers, but because the fiber can be stretched after it leaves the die, very fine fibers can be made. Melt spinning can also be used with polymers such as poly(trimethylpentene), which are not soluble in convenient solvents and are difficult to form by wet spinning. 

Melt-spun fiber is produced from PMP at 280°C and is drawn around three times in air at 95°C its fiber strength is 0.18—0.26 N/tex (2—3 g/den), its elongation is around 30%. Melt-spun hoUow fibers are also manufactured. PMP has one of the highest permeabiHties for gases, and many of its appHcations capitalize on this property. 

Delusterants reduce the transparency, iacrease the whiteness, and alter the fiber s reflectance of light. Ti02 is the delusterant of choice for aU melt-spun fiber types because of its high cover, whiteness, and chemical and thermal stabUity. Nylon is translucent and requires ia most textile and... 

Fibers produced by dry spinning have lower void concentrations in comparison to melt-spun fibers because the presence of solvent molecules causes voids that are often remembered by the polymer. This is reflected by greater densities and lower dyeability for the dry spun fibers. 

Slit and Split Films. Thick incUistiial-giade yams aic often pioduccd by slitting films, providing a less expensive alternative to melt spun fiber. Cast film is slit in the machine direction by parallel rotary knives. The resulting tape can then be cold drawn in an oven in a manner similar to melt spun fibers to produce the final fiber. 

Not only must precursor fibers be self-supporting as extruded, they must also remain intact (e.g. not melt or creep) during pyrolytic transformation to ceramic fibers. Thus, precursor fibers (especially melt spun fibers) must retain some chemical reactivity so that the fibers can be rendered infusible before or during pyrolysis. Infusibility is commonly obtained through reactions that provide extensive crosslinking. These include free radical, condensation, oxidatively or thermally induced molecular rearrangements. 

P. W. Bell and D. D. Edie, Calculated Internal Stress Distribution in Melt-spun Fibers, J. Appl. Polym. Sci., 33, 1073-1088 (1987). 

Among melt-spun fibers, those based on thermotropic liquid-crystalline melts have the highest strength and rigidity reported to date, and appear comparable to polyamides spun from lyotropic liquids-crystalline solutions. This was a very active field of research in the 1970s and later, and many comonomers have been reported. Obviously, these compositions must contain three components at a minimum, but many have four or five com-... 

Figure 7.7. Yield stress vs draw ratio k for SWCNT-PMMA melt spun fibers containing 0 wt% (white), 1 wt% (blue), 5 wt% (red), or 8 wt% (green) of purified soot. Reprinted with permission from Elsevier (21).

Figure 6.13 (cont.) (b) A stabilized, round inviscid melt spun fiber (c) An unstable fiber with Raylei waves frozen on its surface, a condition just before breakup (courtesy of F. Wallenbeiger). 

Polymers from Table II that are typically wet or dry spun are aramids, acrylics, modacrylics, and cellulosics. The polyesters, polyamides, and polyolefins are melt spun fibers. 

Kennedy, J. and Liu, C.-K., Absorbable Melt Spun Fiber Based on Glycolide-containing Copolymer, U.S. Patent (to U.S. Surgical Corp.) 5,425,984,1993. 

In addition, surface forces [240] and shear fields [%, 188, 241-243] have successfully been employed in orienting the LCPs. Solid state extrusion [10, 188] and mdt-spinning [96] produce fibers, with nearly perfect aligoonent of the director axes 0.9). This is demonstrated in Fig. 30. The H NMR spectra Ctop row) refer to melt-spun fibers of LCP 4 (a-CD ) and five different orientations of fiber axis and magnetic field. Drastical lineshape chan are observed when the sample is rotated. A detailed analysis, based on spectral simulations (bottom row), provides the parameters of micro- and macroorder, summarized in Table 9 [96]. 

Lee, S. H., and Youn, J. R., Properties of polypropylene/layered-silicate nanocomposites and melt-spun fibers, J. Appl. Polym. Sci, 109, 1221-1231 (2008). 

High modulus melt-spun PE from Hoechst Celanese Certran has a modulus of about 40 GPa (common unreinforced engineering TPs have a modulus in the range 2.3 to 3 GPa) showed a longitudinal modulus of 37 GPa for imidirectional fiber and 110 MPa longitudinal strength, a transverse modulus of 3.9 GPa and transverse strength 28 MPa. The process continues to be applied to all melt-spun fibers. 

Knot/ straight tenacity % Melt-spun fiber (diameter = 15-25 pm) 50-80 (2)... 

The cross-links formed in the molecular structure are key to the superior heat resistance of XLA. As the temperature increases, crystallites gradually disappear and cross-links take over keeping the network structure retention. After cooling down, crystallites will reform. This makes XLA very different from conventional melt-spun fibers, which rely on crystallites for both recovery and heat resistance. Figure 3.2 shows the percent tenacity retention of chlorine-treated XLA elastic fibers and elas-tane fibers evaluated under accelerated conditions. XLA elastic fiber retains more than 80% of the mechanical tenacity up to 40 hours of treatment. However, the mechanical property of elastane quickly deteriorates to 45% of its starting tenacity within only 10 hours. 

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