Wet-spinning method

In most of the previous work with polyimide fibers, the fibers were spun from poly(amic acid) precursors, which were thermally imidized in the fiber form. However, high degrees of imidization were not achieved. Thus, tensile properties of these polymers were not as good as those of high-performance fibers. Work in our laboratories has shown that when the fibers are spun directly from preimidized polymers, it is possible to achieve tensile properties that are as good or even better than those of poly(p-phenyleneterephthalamide) (PPTA or Kevlar ) fibers. For example, fibers have been prepared from m-cresol solutions of BPDA-PFMB using a dry-jet wet-spinning method. The as-spun fibers were then extensively drawn and annealed above 400°C to achieve excellent mechanical properties. 

A bisphenol A imprinted PES hollow fibre membrane obtained by the dry-wet spinning method was shown to be an interesting alternative to a flat sheet membrane because of its higher surface area [228]. 

Matsumoto, K., Uejima, H., Iwasaki, T., Sano, Y., and Sumino, H. "Studies on regenerated protein fibers 3. Production of regenerated silk fibroin fiber by the self-dialyzing wet spinning method". J. Appl. Polym. Sci. 60(4), 503-511 (1996). 

Figure 4.18 Comparison of the dry jet-wet spinning method used with nematic liquid oystals and the spinning of a conventional polymer (after Jaffe and Jones, 1985).

The linear structure of chitosan is mainly responsible for the fiber forming property. Chitosan fibers are produced by wet spinning method. In general, chitosan is dissolved in acetic acid to give a solution of 3% w/v and then extruded through the spinneret into... 

Wet-spinning method Wet-spinning of PVC fiber was used for the manufacture of Leavil by the Montefibre Company. According to their process, syndiotactic PVC is dissolved in cyclohexanone, and the solution is spun into a coagulating bath of a water-alcohol mixture. 

Khulbe et al. [4] conducted an AFM study of the cross section of UF poly(ether-imide) hollow fibers, fabricated by the dry-wet spinning method at various air gaps. 

Fibers containing intrinsically conductive polymer are manufactured from a composition containing an organic acid salt of an intrinsically conductive polymer, a matrix polymer, and a spinning solvent. Polyaniline is the intrinsically conductive polymer. Polyaniline alone cannot be processed into fiber because of its low solubility (standard wet spinning methods require a polymer concentration of 15-20%). Many polymers can be used as the matrix polymer. For this application, polyacrylonitrile was selected. A variety of solvents can be used but dimethylacetamide was found to be the most useful. 

Charged PVB hollow fiber ultrafiltration membranes were fabricated with perfluorosulfonic acid as additive by a wet-spinning method (28). Perfluorosulfonic acid with N-methyl-2-pyTrolidone promotes an instantaneous demixing mechanism and the precipitation rate increases with the addition of perfluorosulfonic acid. Fibers fabricated with 50% ethanol in aqueous solution as a bore liquid for... 

Fibers were formed using a wet spinning method. The hot cellulose solution was prepared as described above by the method of Jin [10] and modified by Hoepfiier [24]. 

Since PPT melts with decomposition at ca 560°C (36), melt spinning cannot be employed. Thus, solution spinning techniques (31) must be used to prepare fibers. Although dry, wet, and dry jet-wet spinning methods have all been used to... 

Fibers from the anisotropic phase of cellulose/NH3/NH4SCN solution have been spun. High mechanical properties have been obtained with these cellulose fibers giving tenacity above 4.5 g den and modulus above 200 g den The solutions were extmded by the dry-jet wet spinning method. A schematic of this process is displayed in Fig. 12.5. The temperature of the solution was adjusted to 30°C by using a heater block and heater sleeves. 

Membrane surfaces can also be modified by heat treatment. The PES HFMs were prepared by dry-wet spinning method and heated in an oven at 120,150, and 180°C. The membrane shrank by heating. It was noticed that pore size decreased from 8.16 nm for untreated hollow fiber to 3.8 nm with 1 minute heating and then increased to about 6 nm with 5 min heating at 150°C. With an increase in heating temperature, the pore size of the membrane decreases [77,78]. Charkoudian et al. reported increased levels of protein adsorbed in thermally treated poly-acrylamide-modified PVDF microporous membranes in comparison to thermally untreated polyacrylate-modified membranes [79]. 

Polyacrylonitrile (PAN) is produced by the additional polymerization of acrylonitrile always, the second and the third monomers are used for the modihcation of dyeability and spinnability. They can then be spun into fibers by dry or wet spinning methods, such as how Orion with a distinctive dumbbell cross section is spun by dry process produced by DuPont, and Acrilan had circular cross section and is spun by the wet extrusion technique produced by Monsanto. PAN fiber can also get the crimp structure like wool by using the bicomponent spinning process in fiber preparation. Properties of PAN fibers are listed in Table 2.27. 

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