RAPID STABILIZATION OF PITCH FIBER PRECURSOR BY MULTI-STEP THERMAL OXIDATION

摘要

A multi-step oxidation procedure was developed to stabilize an isotropic pitch fiber prior to carbonization. In the first step, the temperature was raised to 170-220℃ in 1 minute and kept isothermally for 4 minutes. The temperature was then increased in the same manner to 250, 300 and 350℃. Stabilized fiber precursors were finally carbonized at 1000℃. The three-step oxidation of 220-250-300℃ required only 15 minutes and stabilized the pitch fiber without fusion. However, the tensile strength of the resultant carbon fiber was 70% of that of the carbon fiber stabilized by a conventional slow heating method (2.5℃/min to 360℃). 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℃ and 220-250-300-350℃, respectively. Oxidized fibers were characterized by differential scanning calorimetry (DSC) in a nitrogen atmosphere. The three-step oxidation of 220-250-300℃ decreased the heat capacity of the fiber but did not completely stabilize the microstructure of the fiber. The four-step oxidation up to 350℃, however, diminished the endothermic peak in the DSC profile seen with fibers oxidized by the three-step procedure. The DSC profile of the fiber prepared by the four-step oxidation was very close to that prepared by the slow heating method.