Processing, structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Abstract

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry-jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent-free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from -50 to 25 degrees C. The effect of fiber processing conditions was studied to understand their effect on the as-spun fiber cross-sectional shape, as well as the as-spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as-spun fibers were then drawn to investigate the relationship between as-spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as-spun fibers with an irregular cross-sectional shape produced using a -50 degrees C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross-section.