Multifilament continuous hollow carbon fiber tows with a honeycomb cross-section have been produced using a gel-spun bicomponent islands-in-a-sea precursor with polyacrylonitrile (PAN) as the sea component and polymethylmethacrylate (PMMA) as the sacrificial island component. The density of the hollow carbon fibers is 1.15 g/cm3, more than 30percent-flag-change lower compared to commercial carbon fibers. The tensile strength of these fibers is in the range of 2.3-3.0 GPa and tensile modulus between 202 and 234 GPa. The tensile strength is over 80percent-flag-change higher than the 1.6 GPa strength value reported earlier for hollow carbon fibers. The specific tensile strength is 30percent-flag-change higher than T300 carbon fibers. The specific tensile modulus is 60percent-flag-change higher than T300 carbon fibers and 20percent-flag-change higher than aerospace grade IM7 carbon fibers. The manufacturing was successfully scaled up from a single filament to 740 filament tow without affecting the carbon fiber structural parameters. The tensile strength is limited by the size of the largest defects present, estimated to be in the range of 40-65 nm for the hollow carbon fibers.
