Kyukoshi method

Figure 6. Flow charts for the preparation of fiber-spinning pitches by the Gundai (dormant mesophase) and Kyukoshi methods.

Figure 7. Relations between softening points, quinoline-insoluble contents, and mesophase contents of precursor pitches prepared by the Gundai and Kyukoshi methods. The volume percentage of mesophase is indicated by the numbers adjacent to some points.

Three points are noteworthy for the Kyukoshi method. (i) Rapid heating of the hydrogenated pitch to above 450°C produces a pitch suitable for smooth spinning. (ii) This pitch appears to be isotropic at the spinning temperature of 370°C. (iii) The viscosity-temperature relationship, plotted in Figure 8 in terms of the Andrade equation... 

The mechanical properties as a function of heat treatment temperature are shown in Figure 9 for fibers prepared by the Kyukoshi method. Fiber heat-treated to 2000°C or higher have strengths above 3GPa (435 kpsi) and tensile moduli of the order of 500 GPa (72 Mpsi). The present authors now believe that, in the near future, it will be possible to produce carbon fiber of equivalent properties by selection of suitable raw pitch materials and by development of specialized pretreatment procedures for the pitch to replace the extensive hydrogenation technique described here. 

Figure 8. Viscosity of mesophase pitches prepared by the Kyukoshi method, with schematic microstructures of fibers spun at temperatures in the range of 300 to 400°C.

Figure 9. Mechanical properties, as a function of heat treatment temperature, of carbon fibers spun from mesophase pitch prepared by the Kyukoshi method.

The introduction of HPCF by Union Carbide in the USA initiated intensive research and development to improve the processability of mesophase pitch (MP). Riggs and Diefendorf in the US worked on a neo-mesophase pitch based on a solvent extraction technique. Yamada and co-workers discovered the pre-mesophase pitch [41,42] using hydrogenation followed by a rapid heat treatment, while workers at the Kyushu Industrial Research Institute in Japan hydrogenated an anisotropic pitch (preferably a coal tar pitch), which after heat treatment produced a dormant mesophase pitch [43,44], a process known as the Kyukoshi method and able to produce a type of carbon fiber intermediate between a GP and HP fiber. Mochida and co-workers used a Lewis acid, such as AICI3, for the catalytic polymerization of an isotropic pitch, but found that an excessive amount of catalyst was required to achieve mesophase formation. 

A method developed by the Kyushu Industrial Research lnstitute(known as Kyukoshi in Japan), utilized hydrogenation of a coal tar pitch, which was first de-ashed, followed by distillation as required and then hydrogenated in the presence of a hydrogen donor solvent such as tetrahydroquinoline ... 

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