Carbon fibers having unique surface geometries, from circular to hollow gear-shaped, are produced from polyethylene using a versatile fabrication method. The resulting carbon fiber exhibits properties that are dependent on processing conditions, rendering them highly amenable to myriad applications. As reported in physorg.com, polyethylene could be turned into something far more valuable through a process being developed at the Department of Energy's Oak Ridge National Laboratory. A team led by Amit Naskar of the Materials Science and Technology Division outlined a method that allows not only for production of carbon fiber but also the ability to tailor the final product to specific applications. Using a combination of multi-component fiber spinning and their sulfonation technique, the team demonstrated that they can make polyethylene-base fibers with a customized surface contour and manipulate filament diameter down to the submicron scale. The patent-pending process also allows them to tune the porosity, making the material potentially useful for filtration, catalysis and electrochemical energy harvesting. The sulfonation process allows for great flexibility as the carbon fibers exhibit properties that are dictated by processing conditions. For this project, the researchers produced carbon fibers with unique cross-sectional geometry, from hollow circular to gear-shaped by using a multi-component melt extrusion-based fiber spinning method. The fiber bundle is dipped into an acid containing a chemical bath where it reacts and forms a black fiber that no longer will melt. This sulfonation reaction transforms the plastic fiber into an infusible form.