Novel process converts polyethylene into carbon fibre

Researchers at the US Department of Energy's Oak Ridge National Laboratory have discovered a new method for converting polyethylene - a common material used in plastic bags - into carbon fibre.

The team also found that they could fine tune the properties of the fibres themselves, allowing different types of carbon fibre to be created for specific applications. "Our results represent what we believe will one day provide industry with a flexible technique for producing technologically innovative fibres in myriad configurations such as fibre bundle or non-woven mat assemblies," said Amit Naskar, who led the team. Using a combination of multi-component fibre spinning and a sulfonation technique, Naskar and his colleagues found they could make polyethylene-base fibres with a customised surface contour and manipulate filament diameter down to the submicron scale. The patent-pending process also allowed them to tune the porosity, making the material potentially useful for filtration, catalysis and electrochemical energy harvesting. It is hoped that it could also be used in the automotive industry to make lightweight, inexpensive car parts. Naskar noted that the sulfonation process allows for great flexibility as the carbon fibres exhibit properties that are dictated by processing conditions. For this project, the researchers produced carbon fibres with unique cross-sectional geometry, from hollow circular to gear shaped by using a multi component melt extrusion based fibre spinning method. "The possibilities are virtually endless," said Naskar. "We dip the fibre bundle into an acid containing a chemical bath where it reacts and forms a black fibre that no longer will melt. It is this sulfonation reaction that transforms the plastic fibre into an infusible form. "At this stage, the plastic molecules bond, and with further heating cannot melt or flow. At very high temperatures, this fibre retains mostly carbon and all other elements volatise off in different gas or compound forms." The findings have been published in the journal Advanced Materials.