High-molecular-weight PAN solutions behave as shear-thinning non-Newtonian fluids; their viscosity decreases as concentration increases, and the spinning dope system exhibits predominantly elastic characteristics. The concentration and temperature of the coagulation bath, as well as the apparent negative draw ratio applied within it, exert a significant influence on the circular cross-sectional shape and surface morphology of the nascent fibers. Under optimized processing conditions-specifically, a coagulation bath concentration of 80% and a temperature of 40°C-nascent fibers possessing excellent surface morphology and superior physical-mechanical properties can be obtained. Following post-treatment processes such as boiling water drawing and steam drawing, high-performance PAN precursor fibers with a tensile strength reaching 0.96 GPa can be successfully produced.
The physical properties of pitch-based carbon fiber precursor fibers vary depending on the specific precursor material utilized. Isotropic pitch-based carbon fibers typically take the form of chopped fibers, featuring diameters ranging from 12 to 18 μm, a density of approximately 1.6 g/cm³, and a relatively low modulus of around 40 GPa. In contrast, mesophase pitch-based carbon fibers are typically produced as continuous filaments, with diameters ranging from 7 to 10 μm; these fibers possess a density between 1.7 and 2.2 g/cm³ and can achieve a modulus ranging from 600 to 965 GPa.
As a critical precursor for carbon fibers, polyacrylonitrile (PAN) possesses a molecular chain structure and thermal stability that enable its precursor fibers to be effectively transformed-during subsequent thermal treatment processes-into carbon fibers characterized by high strength and high modulus.
