Stretching modification on mesophase-pitch-based fibers during carbonization process: From laboratory batch experiments to pilot continuous production

Mesophase-pitch-based carbon fibers (MPCFs) have excellent physical performance and are widely used in many cutting-edge fields. The regulation and control of temperature-dependent crystalline structure is very vital for improving their physical properties. Herein, a stretching technique was applied in the carbonization process to produce performance-improved MPCFs, through testing initially in laboratory batch experiments, and then upgrading into a pilot continuous production. For batch carbonization stretching on a bundle of fixed-length fibers, it is found that applying an appropriate tension helps improve their crystalline structure and physical properties. Compared to the one-stage constant tension, the two-stage variable tension is more conducive to the growth and orientation of graphite microcrystals in MPCFs and the improvement of their physical properties owing to the good match of tension and temperature. For continuous carbonization stretching on a bundle of long filaments, the optimal condition is under a suitable stretching ratio of 0.965 at 500-780 degrees C for 40 min. The tensile strength and modulus of the 300 degrees C-graphitized large-diameter MPCFs rise by similar to 35% and similar to 10%, respectively. The axial electrical resistivity (1.66 mu Omega m) decreases by similar to 25%, while the thermal conductivity (759.64 W/m K) increases by similar to 33%. The effect of the continuous carbonization stretching has been verified to be well accordant with that of the batch in this work, which will pave the road for the wide application of hot stretching in industrial production of high-performance MPCFs.

Automated summary

In this study, a stretching technique was used to carbonize mesophase-pitch-based carbon fibers (MPCFs) and improve their physical properties. The application of tension, whether in batch experiments or continuous production, was found to enhance the crystalline structure and physical properties of the fibers.