Voids in the Carbon Fibers Produced from Lignin and PVA

Abstract

Some kinds of carbon fibers are produced from lignin and PVA. One graphitized and four carbonized grade fibers of this species were selected and the latters were heat-treated up to 2000°C.The pattern of X-ray small angle scattering for the original fibers was observed only in the center, except for the following two: the graphitized grade one and the fiber the precursor of which was dried with a higher speed. With increase of heat-treatment temperature, these patterns streched isotrotropically to wider angle. A weak and circular long periodic pattern was observed for some of the heat-treated fibers.The Porod's law held for all fibers heat-treated at 2000°C and for some fibers heat-treated at lower temperatures.Judging from the scattering power, there would be voids in almost all fibers.The result of the measurement of density showed that there would be open and closed pores in all fibers.Radius of gyration varied over the range of 8-16A. There could be pores with a larger radius of gyration in all of the fibers.The fibers contain more or less sodium and its compounds. An elimination of them with diluted hydrochloric acid had no effect on the profile of X-ray small angle scattering and a little on density.A wavy surface and a cross-section with pores were observed for all fibers. The surface of the original fibers were more complicated than that of their heat-treated products.