Isotropic pitches, fibers from

It was found that melts of copolyesters containing 40-90 mole percent para oxybenzoyl segments exhibited behaviors similar to those of nematic liquid crystals. 

MECHANICAL PROPERTIES OF LIQUID CRYSTALLINE POLYMER CONTAINING 60 MOL. % p-OB 

McFarlane and coworkersL have synthesized other polymers containing other moities that are also known to lead to liquid crystallinity in non-polymeric forms. Thus, a wide variety of high molecular weight copolymers exhibiting liquid crystalline melts may be prepared. Structural shapes consisting of a high degree of molecular orientations and chain extensions may be easily fabricated from such liquid crystalline melts. 

Polymers with Liquid Crystalline Side Chains 

Extensive work has been done in a number of labora-toriesZ-lUL on the synthesis and characterization of several polymers with liquid crystalline side chains. Various of the papers in this monograph deal with various aspects of such polymers containing mesomorphic side chains. A review of the potential applications of such side chain liquid crystalline polymers therefore, will be redundant. 

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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... 

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. 

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. 

Two categories of pitch-based fiber exist isotropic carbon fiber produced from an isotropic pitch precursor, and an oriented, anisotropic fiber produced from a mesophase pitch precursor. Isotropic fibers were developed from low melting point isotropic pitches The precursor was melt-spun into fibers, which were oxidized to render them infusible, and then carbonized. Their low strengths and moduli make these fibers unsuitable for use in advanced composites. Orientation was accomplished by a hot-stretching process (>2200°C), but it is accompanied by the same processing difficulties encountered in the rayon precursor process. A different approach was suggested by the discovery of carbonaceous mesophase. ... 

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