Characterization of amorphous carbon fibers produced from thermally stabilized polyamide 6 fibers

Abstract

Amorphous carbon fiber from polyamide 6 (PA6) precursor was produced using a multi-step procedure consisting of oxidative stabilization in air at 180℃ in the presence of cupric chloride impregnation, pre-carbonization at 250℃ and carbonization at temperatures ranging from 500℃ to 1000℃ in nitrogen. The results obtained from thermal analysis data suggested that cupric chloride impregnation enhanced thermal stability. During the oxidative stabilization process, a polymorphic structure consisting of α- and γ-phases was eliminated due to the decrystallization process. The pre-carbonization step was found to be necessary to enhance the thermal stability of oxidatively stabilized PA6 fiber prior to carbonization. The results suggested that the pre-carbonization step improved the aromatization and crosslinking reactions. The results obtained from the experimental data suggested that the carbonization temperature had an effective role on the molecular structure and properties of the resulting carbon fibers. The carbon fibers obtained from stabilized and pre-carbonized PA6 fibers showed physical and structural changes with rising temperature. They were characterized by a reduction in fiber diameter, linear density, carbon fiber yield, hydrogen and nitrogen content values due to the removal of non-carbon elements together with increases in the values of density, crystallite thickness, carbon content, C/H ratio and electrical conductivity values. The results obtained from X-ray diffraction, IR spectroscopy and elemental analysis suggested that the crystalline structure was totally lost and converted to a carbonized structure at 500℃ and above due to the formation of an amorphous carbon structure during carbonization reactions.