Low-density and high-modulus carbon fibers from polyacrylonitrile with honeycomb structure

The density of commercially available polyacrylonitrile-based carbon fibers is in the range of 1.75–1.93 g/cm3. It will be of great benefit to reduce the density of carbon fiber without compromising mechanical properties, so that high-performance structures made from such fibers can be lighter than those made from the solid carbon fibers. With the goal to produce high-strength and high-modulus carbon fibers with densities in the range of 0.9–1.3 g/cm3, polyacrylonitrile (PAN) based precursor fibers were produced with a honeycomb structure. Using dry-jet wet spinning and an islands-in-a-sea geometry bi-component spinning method, honeycomb precursor fibers were manufactured that consisted of PAN as the sea component and poly(methyl methacrylate) (PMMA) as the islands component. Subsequently, the precursor fibers were stabilized and carbonized to produce hollow carbon fibers. Resulting carbon fibers have an estimated density of around 1.2 g/cm3 with high tensile modulus of up to 209 N/tex. Raman spectroscopy mapping of the carbonized honeycomb fiber cross-section exhibited a strong Raman G-band intensity not only at the outer surface of the carbon fiber but also at the surface of inner walls of the honeycomb structure, suggesting that highly ordered graphitic structure was developed at these regions.