AUTHOR: Rodney Andrew
Center for Applied Energy Research, University of Kentucky, Lexington, KY 40511-8410
Our interests have focused on the synthesis of carbon fibers and activated carbon fibers from a range of isotropic pitch precursors of different origins, including coal extracts, to ascertain the suitability of these materials for fiber production. The overall aims are to elucidate the basic relationships between precursor composition and properties and: the ability to form fibers; the mechanisms and kinetics of the stages required to produce carbonized and activated fibers; and their structure and properties.
Changes in fiber weight that occur during the oxidative stabilization of green fibers are inversely related to the observed axial contraction. The weight gain upon stabilization also increases, and the contraction decreases, with increasing pitch carbon content and aromaticity while the opposite occurs with increasing hydrogen and heteroatom (H, N, O and S) content. Similar trends are found for fiber carbonization. The combined effects of stabilization and carbonization give a fiber yield of between 50 to 86% of the green fibers, with axial contractions of 12 to 28%, the highest yield corresponding to the smallest contraction. The net yield increases with pitch carbon content and aromaticity, and decreases with heteroatom content, while the overall axial contraction decreases. The fiber tensile strength was found to increase with precursor carbon content, carbon yield and aromaticity. The activation rate of the derived fibers increased with increasing heteroatom content, especially oxygen content. While most fibers were microporous upon activation, fibers from shale oil and the subbituminous coal extract, developed a more mesoporous structure.
In this presentation, we describe how the properties of the precursor determine the preparation that is required for fiber spinning, and how they influence the processes of fiber stabilization, and carbonization to form fibers. In continuing work, we will address the synthesis and properties of novel fibers formed from carbon nanotube doped pitch, as well as a novel fiber spinning technique under development at CAER.