Unveiling the microcrystal structure evolution of carbon fibers induced by thermal soaking of mesophase pitch.

Carbon fibers produced from mesophase pitch are superior in many properties such as high thermal conductivity and high tensile modulus, which originated from the high graphitizability and high carbon yield of the raw materials. Any variation in mesophase pitch microstructure will be inherited in derived carbon fibers. Herein, we monitored the microcrystal structure evolution of carbon fiber derived from thermal soaked mesophase pitch and the caused variation in mechanical properties. Results showed that mesophase pitch with prolonged soaking time from 1 to 12 h produced the carbon fibers with improved microcrystal structure, reduced diameter, and crack angle, contributing to an apparent increase in tensile strength from 1.70 to 2.72 GPa and tensile modulus from 152 to 246 GPa. Thermal soaking upon elevated temperature from 320 to 335 °C also contributes an improvement in microcrystalline development. However, the attendant increment in diameter and open crack angle lead to deterioration in tensile strength and modulus, the highest value of which is only 1.53 GPa and 190 GPa. This work provides useful information on thermal soaking parameter selection and is of particular interest for future optimization of carbon fiber production. [ABSTRACT FROM AUTHOR]