Carbon Fibers from Isotropic Pitch

Low-cost carbon fibers are produced from an isotropic pitch with a low-softening point. The precursor is melt-spun, thermoset at relatively low temperature, and carbonized. The resulting fibers generally have low strength and modulus ( 35 - 70 GPa). They are suitable for insulation and filler applications. Their cost dropped to less than 20/kg in 1992.  

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Korai Y, Ishida S, Watanabe F, Yoon SH, Wang YG, Mochida I, Kato I, Nakamura T, Sakai Y, Komatsu M, Preparation of carbon fiber from isotropic pitch containing mesophase spheres. 

Carbon fibers from isotropic pitch Isotropic pitch or a pitch-like material, such as molten polyvinyl chloride, is melt spun at high strain rates to align the molecules parallel to the fiber axis. The thermoplastic fiber is then rapidly cooled and carefully oxidized at a low temperature (<100 °C). The oxidation process is rather slow, so as to ensure stabilization of the fiber by cross-linking to make it infusible. However, upon carbonization, relaxation of the molecules takes place, producing fibers with no significant preferred orientation. This process is not industrially attractive due to the lengthy oxidation step, and because only low-quality carbon fibers with no graphitization are produced. These fibers are used as fillers in various plastics to form thermal insulation materials. 

Fibers produced from pitch precursors can be manufactured by heat treating isotropic pitch at 400 to 450°C in an inert environment to transform it into a hquid crystalline state. The pitch is then spun into fibers and allowed to thermoset at 300°C for short periods of time. The fibers are subsequendy carbonized and graphitized at temperatures similar to those used in the manufacture of PAN-based fibers. The isotropic pitch precursor has not proved attractive to industry. However, a process based on anisotropic mesophase pitch (30), in which commercial pitch is spun and polymerized to form the mesophase, which is then melt spun, stabilized in air at about 300°C, carbonized at 1300°C, and graphitized at 3000°C, produces ultrahigh modulus (UHM) carbon fibers. In this process tension is not requited in the stabilization and graphitization stages. 

Characterization of Pore Distribution in ACF Prepared from Isotropic Pitch-Based Carbon Fiber... 

Until 1987, the only route to short carbon fibers was a metal catalyzed chemical vapor deposition. Since then, a novel process has become available [19] that facilitates the growth of discontinuous carbon fibers from mesopitch by a continuous liquid phase centrifuge process. Pitch may be considered to consist of a complex mixture of polycyclic aromatic hydrocarbons. It is a semisolid at room temperature but, depending on the composition, it melts above 100°C. Pitch has two phases, a high melting anisotropic, and a low melting isotropic, phase. The anisotropic phase, called mesopitch, is preferred for this process. 

Pitch as a precursor material is cheaper than PAN as a precursor fiber, but the conversion of pitch into mesophase pitch and subsequent fiber formation is complex and costly. When a pitch is not transformed into a mesophase and is spun as an isotropic liquid, the resulting carbon fibers have extremely poor mechanical properties. These considerations explain why more than 90% of today s carbon fibers are fabricated from PAN based precursors. Processes for fabricating carbon fibers from PAN or pitch based precursor fibers differ in important aspects, but also share important commonalties (Figure 2). Finally, the carbon yield from PAN based precursor fibers is 50%, that from mesophase pitch is 70-80%, and that from rayon is 25%. 

The oxidation reaction starts at a temperature that depends on composition, structure, and microtexture. For example, the oxidation of carbon fibers derived from isotropic pitch precursor fibers in flowing air starts at about 400°C whereas that of the mesopitch based UHM fibers starts at a higher temperature [64]. At a given temperature, the variation of the weight loss, AJmo, as a function of time is linear, to a first approximation, within a rather large domain of weight loss [65-66]. This property is used to characterize the oxidation rate with a kinetic constant, k, defined as ... 

The.se fibers are sometimes referred to as isotropic carbon fibers, since they are made from isotropic pitch. These pitches are prepared from high boiling fractions of petroleum feedstocks, usually heavy slurry oils produced in catalytic cracking of crude oil. 

Figures 1.6a and 1.6b present the Nj isotherms for ACs prepared using two types of carbon fiber (CF) precursors [88,98] (1) anisotropic PAN-based carbon fibers from Hexcel, and (2) isotropic coal tar-pitch-based fibers from Donac. It...

Park, S. H., C. Kim, Y. I. Jeong, D. Y. Lim, Y. E. Lee, and K. S. Yang (2004a). Activation behaviors of isotropic pitch-based carbon fibers from electrospinning and meltspinning. Synthetic Metals 146(2) 207-212. 

Low density, carbon fiber-carbon binder composites are fabricated from a variety of carbon fibers, including fibers derived from rayon, polyacrylonitrile (PAN), isotropic pitch, and mesophase pitch. The manufacture, structure, and properties of carbon fibers have been thoroughly reviewed elsewhere [3] and. therefore, are... 

A recently developed adsorbent version of ORNL s porous carbon fiber-carbon binder eomposite is named carbon fiber composite molecular sieve (CFCMS). The CFCMS monoliths were the product of a collaborative researeh program between ORNL and the University of Kentueky, Center for Applied Energy Researeh (UKCAER) [19-21]. The m.onoliths are manufactured in the manner deseribed in Section 2 from P200 isotropic pitch derived fibers. While development of these materials is in its early stages, a number of potential applieations can be identified. 

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