Fiber processing gel-spinning

Spectra AUied Signal s trade name for its ultrathin polyethylene fibers that are about 10 times stronger than steel. See fiber processing, gel-spinning fiber processing, solution-spinning. 

Rotations around torsional barriers induce changes in chain conformation. For conjugated systems like polydiacetylenes, flow-induced changes in chain conformation can have a profound influence on the photon absorption and electronic conductivity properties of the material [73]. Flow-induced changes in molecular conformation form the basis for several technically important processes, the best known examples are the production of oriented fibers by gel spinning [74], the compatibility enhancement [75] and the shear-induced modification of polymer morphology [76]. 

Cationic dyes are also used to dye polyacrylonitrile fibers during the spinning process either from dimethylformamide solution or in the gel stage subsequent to aqueous spinning processes. 

Figure 4.11 Flow diagram of the gel-spinning process of making ultra high molecular weight polyethylene fiber.

In the reinforcing sector, a-Al203-fibers are the furthest in development. Low diameter fibers are obtained by the sol-gel process, the spinning of solutions or suspensions and from melts. 

We close this section with a few comments regarding the ultrahigh-modulus acrylic fibers. It is estimated that the theoretical crystalline modulus for polyethylene is 240 GPa hence there has been an intense effort over the last 10-15 years to develop spinning processes to exploit the high-modulus potential. This goal has been achieved by gel-spinning techniques [177]. Allen et al. [178] have estimated the theoretical modulus that might be obtained for... 

PAN by use of gel-spinning or other techniques to create a completely extended chain. Their estimate, based on a comparison of the rod-like PAN conformation with helical chain conformations of other polymers, is that the maximum tensile modulus of atactic PAN would be about 55 GPa. They conclude that PAN with ultrahigh modulus cannot be made by gel spinning, or by any other means, due to the intrinsic chain properties. It is proposed that the strong intramolecular nitrile repulsions that cause the PAN to adopt a rod-like, semiextended conformation do not allow the chain to unravel completely from its semiex-tended conformation. Attempts to develop gel-spinning processes in acrylic fibers are discussed in Section 12.5.4. 

H. Yasuda et al.. Gel spinning processes, in Advanced Fiber Spinning Processes, P.T. Nakajima, Ed., Woodhead Publishing Limited, Cambridge, p. 174 (1994). 

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