RAPID STABILIZATION OF PITCH FIBER PRECURSOR BY MULTISTEP THERMAL-OXIDATION

A multi-step oxidation procedure was developed to stabilize an isotrop ic pitch fiber prior to carbonization. In the first step, the temperat ure was raised to 170-220 degrees C in 1 minute and kept isothermally for 4 minutes. The temperature was then increased in the same manner t o 250, 300 and 350 degrees C. Stabilized fiber precursors were finally carbonized at 1000 degrees C. The three-step oxidation of 220-250-300 degrees C required only 15 minutes and stabilized the pitch fiber wit hout fusion. However, the tensile strength of the resultant carbon fib er was 70% of that of the carbon fiber stabilized by a conventional sl ow heating method (2.5 degrees C/min to 360 degrees C). The four-step oxidation, taking 20 minutes in total, was more effective. The tensile strength of the carbon fiber was 82 and 88% by procedures of 220-250- 300-300 degrees C and 220-250-300-350 degrees C, respectively. Oxidize d fibers were characterized by differential scanning calorimetry (DSC) in a nitrogen atmosphere. The three-step oxidation of 220-250-300 deg rees C decreased the heat capacity of the fiber but did not completely stabilize the microstructure of the fiber. The four-step oxidation up to 350 degrees C, however, diminished the endothermic peak in the DSC profile seen with fibers oxidized by the three-step procedure. The DS C profile of the fiber prepared by the four-step oxidation was very cl ose to that prepared by the slow heating method.