Characterization of Pitch-based Carbon Fibers. Part 1. Carbonization Behavior of Stabilized Mesophase Pitch Fibers.

Abstract

Stabilized pitch fibers, precursors of high performance carbon fibers, have been prepared on a laboratory scale by spinning from mesophase coal tar pitch and then oxidizing in air at 310°C. Their physical and chemical behaviors during carbonization process (400-2, 300°C) have been investigated by using thermogravimetric analysis (TGA), gas adsorption technique and X-ray photoelectron spectroscopy (XPS). Weight losses of the stabilized pitch fibers were observed in the temperature range from 400 to 800°C, with the maximum rate of weight loss at 450-550°C. However, in the range 800-1, 000°C an increase in the specific surface area took place, which was accompanied with a structural transformation from a rheological state to infusible hydrocarbon polymers designated as coke. The surface functional groups produced by oxidization at 310°C in air disappeared below 600°C. However, the surface oxygen-containing functional groups appeared again when carbonization temperature was raised to 1, 000°C. The C-1s bearing hydroxyl group increased with increasing carbonization temperature from 1, 000 to 2, 000°C. Since such groups decreased their intensity by etching, it is concluded that the surface oxides are produced by oxygen and/or water both of which are contaminants of the stream during carbonization.