Spinning solutions

The overall performance difference between the artificial fibroin silk and natural silk is induced by many factors. Composition of the spinning dope is critical but not the only factor. Important to understand is that the spinning process which determines the condensed structure of silk is crucial. It suggest that knowing the spinning process details it should be feasible to produce high-performance silk artificially and design silk. 

Regenerated spidroin and fibroin dissolved in various solvents are used as spinning dope while the coagulation baths are mainly alcohol (Table 4). In addition certain fiber post-treatments, such as drawing, are used as well. 

The wet spinning of regenerated spidroin was reported in the early 1990s by Jelinski et al. They dissolved spider silk in hexafluoroisopro-panol (HFIP) at a concentration of 2.5 wt% to produce an artificial fiber using water, methanol, isopropanol, and acetone as coagulation bath. The reconstituted silk could only be shaped in acetone but the structure 

Pioneering work in fibroin wet spinning can be traced back to 1930s. After that, little work has been done until the late 1980s, when more research was done to investigate the spinning dope systems, and structure and properties of the artificial fibroin silk. The composition of the dope is very important to the properties of the final fiber. Several kinds of solvents, such as LiBr—EtOH, Ca(NOo,)2—MeOH, formic acid, HFIP, hexafluoro acetone (HFA), and so on, are used to prepare the spinning dope (Table 4). Very recently, an ionic liquid was used as dope solvent (Phillips et al., 2005). 

Hudson et al. used Ca(NC 3)2—MeOH to dissolve silkworm silk and did not manage to obtain good fibers directly. They also casted film from such a solution and then dissolved the film in formic acid and trifluoroacetate acid 

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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...

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

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. 

Spinn-faser, /. flber for spinning, textile flber specif., staple rayon, -fett, n. (Textiles) mill oil. -fliissigkeit, /. spinning solution, spin-... 

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. 

Copolymers of acrylonitrile are sensitive to heat, and melt spinning is not used. Solution spinning (wet or dry) is the preferred process where a polar solvent such as dimethyl form amide is used. In dry spinning the solvent is evaporated and recovered. 

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. 

Fe(6-Mepy)3tren](PF6)2- Within the series of iron(II) complexes of the type [Fe(6-Mepy)3 (py) tren](PFg)2 containing the hexadentate ligand tris[4-(6-R)-2-pyridyl]-3-aza-3-butenyl]amine, R = H or CH3, the compounds with X = 1, 2 show a similar HS <- LS transition in solution as well as in the solid state [170]. In solution, spin-state conversion rates have been obtained as shown in Table 3. The complex with x = 0 is pure HS in solution, whereas in the solid state a gradual transition is observed extending over the range... 

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... 

Solution prepregging, 20 284-285 Solution processing, 14 80 Solution process, of ethylene-propylene polymer manufacture, 10 708-710 Solution properties of lignin, 15 13 of polyampholytes, 20 479 ofVDC copolymers, 25 703-706 Solution spectrophotometry, 9 232 Solution spinning... 

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. 

The deuterium NMR spectra of toluene-d0 in aPS solutions consists of two resonances which are resolved and assigned to the methyl and aromatic groups. In these solutions spin-spin or dipolar couplings are small and consequently are not observed. As the temperature is lowered, the aromatic resonance systematically broadens while the methyl resonance remains relatively constant in width. The linewidths of the aromatic resonances are the same as those which would be predicted from the T2 measurements reported below. The separated resonances make it possible to determine the relaxation times of each type of resonance. 

Although the term dry solution spinning may seem like an oxymoron, it simply describes a process by which a polymer is dissolved in an appropriate solvent, and the solution is pumped through a spinneret in much the same manner as in melt... 

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... 

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