Converting an Abundant Polymer Into Carbon Fibers

Carbon fibers made from polyethylene
Carbon fibers made from polyethylene.

Polyethylene from plastic bags could be turned into valuable carbon fibers, thanks to a process developed by scientists at the Oak Ridge National Laboratory (ORNL). In a paper published in Advanced Materials on Tuesday, March 27, Amit Naskar and colleagues described a way to make carbon fibers specifically tailored for different applications.

Among other things, carbon fibers are used to make composite polymer materials. The global demand for carbon fibers is estimated to be $13.2 billion for 2012. The aircraft and aerospace, wind energy, and automotive industries are among the largest users of carbon-fiber materials.

According to an accompanying ORNL press release by science writer Ron Walli:

‘Our results represent what we believe will one day provide industry with a flexible technique for producing technologically innovative fibers in myriad configurations such as fiber bundle or non-woven mat assemblies,’ Naskar said.

The investigators used multi-component fiber spinning combined with a sulfonation technique in their process. Their method allowed them to make polyethylene-based fibers with surface contours and filament diameters, as low as submicrons, tailored to specifications for a given application.

Naskar and colleagues can also manipulate the porosity so the fibers can be used for potential applications such as filtration and electrochemical energy harvesting. The cross-sectional geometries of the carbon fibers could be made to specifications.

The press release has Naskar describing the process:

‘We dip the fiber bundle into an acid containing a chemical bath where it reacts and forms a black fiber that no longer will melt,’ Naskar said. ‘It is this sulfonation reaction that transforms the plastic fiber into an infusible form.

‘At this stage, the plastic molecules bond, and with further heating cannot melt or flow. At very high temperatures, this fiber retains mostly carbon and all other elements volatize off in different gas or compound forms.’

The investigators say their method can produce lightweight carbon-fiber materials that can be used, for example, in the auto industry to make cars that get more miles per gallon and not hinder safety or comfort. The raw material for the process is polyethylene, which can be cheaply and easily obtained from plastic bags found at grocery stores and  scraps from carpet backing.

Source: “ORNL process converts polyethylene into carbon fiber,” Oak Ridge National Laboratory press release, 03/27/12
Image by ORNL, used under Fair Use: Reporting.

Rajendrani "Raj" Mukhopadhyay is a science writer and editor who contributes news stories and feature articles on scientific advances to a variety of magazines. Raj holds Ph.D. in biophysics from Johns Hopkins University.