Dry-jet wet spinning processing

In a typical commercial dry jet-wet spinning process, PPT polymer of inherent viscosity 6.0 dL/g is added to 99.7% sulfuric acid in a water-jacketed commercial mixer in a ratio of 46 g of polymer to 100 mL of acid. The mixture is sealed in a vacuum of 68.5—76 mL of mercury. Mixing takes place for 2 h... 

In both cases a dry-jet wet-spinning process is used employing coagulation baths of water or water/methanesulphonic acid. 

Method to Trace the Evolvement of Morphology in a Dry-Jet Wet Spinning Process... 

Nascent fiber in a dry-jet wet-spinning process with a reasonable air-gap distance. (Short-range and random chain structure)... 

FIGURE 5.68 Schematic of skin morphologies in the wet-spinning and dry-jet wet-spinning processes. (After Chung, T. S. and Hu, X. 1997. /. Appl. Polym. Sci., 66, 1067. With permission.)... 

Extrusion of the highly viscous spinning dope at elevated temperatures through an air gap into a coagulation bath (dry-jet wet-spinning process)... 

FIGURE 10.45 Dry-jet wet-spinning process for cellulose solutions in anhydrous phosphoric acid (Akzo process). (From Boerstoel, H., Liquid Crystalline Solutions of Cellulose in Phosphoric Acid for Preparing. Cellulose Yarns, Ph.D. dissertation, University of Groningen, 1998.)... 

Kwolek [106] demonstrated in her early work at DuPont that p-aramid fibers could be spun from amide and salt solutions using a conventional wet-spinning process. These solutions were typically of low concentration. The resulting fibers had low strength but high modulus after heat treatment. In later development,p-aramid fibers were spun from more concentrated solutions using dry-jet wet-spinning processes [107]. These solutions contained aramid polymer above a critical solids concentration and were anisotropic. 

Heat treatment increases the crystallinity of the core (211,213). The magnitude of the skin-core differences is believed to result from the dry-jet wet spinning process involving diffusion of the solvent and fiber coagulation. 

High modulus fibers from lyotropic aromatic polyamides, poly(p-phenylene terephthalamide) (PPTA), were first conunercialized imder the Kevlar trademark by DuPont [414]. The aromatic polyamides, or aramids, are produced by a dry jet-wet spinning process where the nematic structure in solution is responsible for the high modulus fiber performance [415-419]. Another class of lyotropic fibers, also produced by dry jet-wet spinning, are the rigid rod polymers developed as part of the U.S. Air Force Ordered Polymers Program [420-424]. The most conunon of these ordered polymers, poly(p-phenylene benzobisthiazole) (PBZT), is difficult to process, but it exhibits the highest tensile properties of all the LCP fibers produced to date. 

In the dry-jet wet spinning process, the polymer solution is extruded from a dry jet and subsequently followed by coagulation as in conventional wet spinning. The polymer solution enters into an air gap before it is precipitated in the coagulation bath, hence the name dry-jet wet spinning. This method can allow stress relaxation for polymer chains in the air gap, and as a result the as-spun fibers are less oriented and more uniform than those from an immersed jet. This permits orientation by subsequent drawing to produce fibers with higher tenacity. 

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