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1 High-Performance Fiber Technology
Pages 6-17

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From page 6...
... , the orientation of the layered carbon planes, and the degree of crystallization. Commercial carbon fibers are made by extrusion of some organic precursor material into filaments, followed by a carbonization process to convert the filaments into carbon.
From page 7...
... PAN-Based Carbon Fiber More than 90 percent of all commercial carbon fibers are produced by the thermal conversion of PAN precursor fibers. PAN-based carbon fibers are produced in three distinctly separate process steps: polymerization and wet spinning, stabilization, and carbonization.
From page 8...
... This step drives off most of the non-carbon elements, creating a carbon fiber. Since the PAN precursor is approximately 67 percent carbon, it is not surprising that the overall process conversion efficiency for PAN-based fibers (pounds of carbon fiber per pound of precursor fiber)
From page 9...
... However, the defects inserted by crimping, as well as the difficulty in maintaining uniform tension, small oxygen concentration gradients, and a uniform temperature profile, result in carbon fibers from the large textile tows having slightly lower mean strength and greater strength and stiffness variability compared to SAF-based materials. Pitch-Based Carbon Fiber Like PAN-based carbon fibers, the peculiarities of pitch-based fibers are the direct result of the precursor and the process used to convert it to fiber form.
From page 10...
... This, in addition to developing purer mesophase precursors, has allowed the introduction of new varieties of pitch-based carbon fibers with improved tensile strengths. Similarly, manufacturers such as Cytec have begun using improved mesophase precursors and linearizing the transverse texture during extrusion to create new varieties of pitch-based carbon fibers with thermal conductivities that are at least three times that of copper.10 Most agree that these highly ordered textures can be produced only by using a liquid crystalline precursor.
From page 11...
... As a result, PAN-based carbon fibers have a low degree of graphitization. The turbostratic layers in PAN-based carbon fibers appear to follow the original fibrillar structure of the PAN precursor fiber.
From page 12...
... In other words, polymeric precursor fibers, such as PAN fibers, offer natural advantages when compression properties are critical. Developing superior compressive properties in pitch-based carbon fibers could be much more difficult.
From page 13...
... FIGURE 1.4 Specific tenacity versus specific modulus for several advanced organic fibers. DATA SOURCE: Composites Design.
From page 14...
... To achieve melt processibility into fibers, various copolymer compositions have been used and materials have to be spun at low molecular weight. To obtain adequate physical properties, a slow heat treatment process has to be applied.
From page 15...
... M5 is a rigid polymer spun from an anisotropic solution; its properties are given in Table 1.3. While the tensile properties realized are similar to those of PBO, the fiber offers potential for significant improvement of compressive properties above those of any of the commercial organic fibers.
From page 16...
... The new fiber M5, which is in precommercial development, offers a potential for a unique combination of properties that promises a unique set of applications. Raw Materials for Organic Fiber Development The development of advanced organic fibers is a complex and expensive endeavor.
From page 17...
... However, there is general agreement that the strength values attained for organic fibers are further from theoretical values than are the modulus values. For example, demonstrated values of strength are estimated at 30 to 50 percent of theoretical expectations.


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