In-situ doping B4C nanoparticles in PAN precursors for preparing high modulus PAN-based carbon fibers with boron catalytic graphitization

The high modulus PAN-based carbon fibers (CFs) were prepared using the B4C-doped PAN as a precursor which was synthesized by in-situ polymerization of acrylonitrile monomer with B4C nanoparticles, and were characterized to investigate the effects of B4C nanoparticles on stabilization and carbonization behaviors of the as-spun fibers and to compare the structural properties of the B4C-doped CFs (B-CF) with the pristine CFs (P-CF). The results showed that the B-CF-1000 prepared at carbonization temperature of 1000 degrees C had lower tensile strength than P-CF-1000 due to the defects and disordered structures in the B-CF-1000 caused by the doped B4C, while the B-CF-3000 prepared at graphitization temperature of 3000 degrees C had much higher tensile modulus of 399 GPa than P-CF-3000 of 251 GPa under the effect of boron catalytic graphitization. Moreover, the skin-core structure of B-CF had significantly improved compared to P-CF, which was caused by the fact that B4C inhibited the oxidation reaction and limited the shrinkage of the fibers during stabilization so as to benefit the entry of oxygen into the fiber core. The above results indicated that the in-situ doped B4C does play a significant role in catalytic graphitization and improving microstructure of PAN-based CFs.