Fiber solution spinning

Fig. 20. A hoUow-fiber solution-spinning system. The fiber is spun into a coagulation bath, where the polymer spinning solution precipitates forming the...

Doped silicon, conductivity in, 23 35 Doped/undoped electrochromic organic films, 6 580-582 Dope-dyeing, 9 197 Dope-making process, in acrylic fiber solution spinning, 11 204 Dope solids, in air gap spinning, 11 209 Doping, 23 838—839 calcium, 23 842-844 conducting polymers, 7 528-529... 

Two methods are used to prepare hollow fibers solution spinning and melt spinning [98,99], The most common process is solution spinning or wet spinning, in which a 20-30 wt% polymer solution is extruded and precipitated... 

Key words synthetic fibers, fiber extrusion, fiber melt spinning equipment, fiber solution spinning processes. 

One of the principal problems in early commercialization of acryUc fibers was the lack of a suitable spinning method. The polymer caimot be melt spun, except possibly at high pressure in the presence of water. Solution spinning was the only feasible commercial route. However, hydrogen bonding between... 

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. 

Fig. 19. Twin-orifice spinnerette design used in solution-spinning of hoUow-fiber membranes. Polymer solution is forced through the outer orifice, while...

The second type of hoUow-fiber module is the bore-side feed type illustrated in Figure 23b. The fibers in this type of unit are open at both ends, and the feed fluid is usually circulated through the bore of the fibers. To minimize pressure drops inside the fibers, the fibers often have larger diameters than the very fine fibers used in the shell-side feed system and are generally made by solution spinning. These so-called capillary fibers are used in ultrafiltration, pervaporation, and in some low to medium pressure gas appHcations. Feed pressures are usually limited to less than 1 MPa (150 psig) in this type of module. 

Melt spinning polyesters is preferred to solution spinning because of its lower cost. Due to the hydrophobic nature of the fiber, sulfonated terephthalic acid may be used as a comonomer to provide anionic sites for cationic dyes. Small amounts of aliphatic diacids such as adipic acid may also be used to increase the dyeability of the fibers by disturbing the fiber s crystallinity. 

Dynel, a modacrylic fiber, is produced by copolymerizing vinyl chloride with acrylonitrile. Solution spinning is also used where the polymer is dissolved in a solvent such as acetone. After the solvent is evaporated, the fibers are washed and subjected to stretching, which extends the fiber 4-10 times of the original length. 

Under these conditions, many types of continuous oxide fiber were developed. The physical properties of these oxide fibers are shown in Table 2 [11]. Methods for preparation of these oxide fibers include spinning of a sol, a solution, or slurry, usually containing fugitive organics as part of a precursor. 

Spinnerets, for olefin fiber extrusion, 22 627, 630-631, 11 231-232 Spinner flasks, 15 691-692 Spinning. See also Solution spinning Yarn spinning technologies air gap, 11 209 of continuous-filament yarns,... 

Melt spinning is not used for polyacrylics because they are sensitive to high temperatures. They actually begin to decompose before they reach melting temperature. Solution spinning is used instead. The dried polymer is dissolved in a polar solvent like acetone or dimethyl formamide (DMF). The spinning mechanics are otherwise the same, except the solvent is recovered as it vaporizes, immediately after the extrusion through the spinneret. Most acrylics are sold and used in the form of staple fiber. 

Sollinger and Voges8 at Akzo Nobel (Obemburg, Germany) used off-line transmission NIR to monitor the key quality parameters in cellulose fiber (viscose) spinning solutions over time. The business value lay both in reducing the time and cost of analysis by consolidating four or... 

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