Draw-Induced Structural Optimization of PAN-Based Carbon Fibers During High-Temperature Carbonization

This study investigates the effect of tensile strain during high-temperature carbonization on the microstructural development and mechanical properties of polyacrylonitrile (PAN)-based carbon fibers. The wet-spun stabilized PAN precursor fibers were carbonized at 1400 °C under various tensile draw ratios (0%, 5%, 10%, and 15%), followed by stress-free graphitization at 2400 °C in an argon atmosphere for 1 h to isolate the effects of the carbonization-stage tension. Structural characterization using XRD, 2D-XRD, Raman spectroscopy, and HR-TEM revealed that moderate tensile strain (5-10%) promoted significant improvements in crystallinity, orientation, and graphene layer alignment. Notably, the fiber drawn at 10% performed the best, with a reduced interlayer spacing (d₀₀₂), increased lateral crystallite size (L_a), high orientation factor, and minimal turbostratic disorder. These structural developments translated into the best mechanical properties, including a tensile strength of ~2.44 GPa, a Young's modulus of ~408.6 GPa, and the highest measured density (1.831 g/cm³). In contrast, excessive strain (15%) induced microstructural defects and reduced performance, underscoring the detrimental effects of overstretching. The findings highlight the critical role of draw control during carbonization in optimizing the structure-property relationships of carbon fibers, offering valuable insight for the design of high-performance fiber processing strategies.