Researchers have found a way to transform plant waste left behind during industrial processes into carbon fibre that is strong enough to be used to make parts for cars or planes.
The plant waste, lignin, is left over in the form of a residue when plants and trees are used to make a variety of products, including paper and ethanol.
Conventionally it is considered a useless by-product, and often is burnt or finds its way to a landfill site, however scientists at Washington State University (WSU) have successfully developed a method to turn it into automobile-grade carbon fibre, giving it a valuable use.
“Lignin is a complex aromatic molecule that is mainly burned to make steam in a biorefinery plant, a relatively inefficient process that doesn’t create a lot of value,” said study lead investigator Dr Birgitte Ahring, a professor at The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, WSU.
“Finding better ways to use leftover lignin is really the driver here. We want to use biorefinery waste to create value. We want to use a low-value product to create a high-value product, which will make biorefineries sustainable.”
The research, which is presented today at the 254th National Meeting & Exposition of the American Chemical Society, also presents a more affordable alternative to conventional carbon fibre, which is normally made from the expensive, non-renewable polymer polyarylonitrile (PAN).
“PAN can contribute about half of the total cost of making carbon fiber,” explained Dr Jinxue Jiang, a postdoctoral fellow in the Ahring laboratory at WSU. “Our idea is to reduce the cost for making carbon fiber by using renewable materials, like biorefinery lignin.”
However, while the lignin-based carbon fibre makes use of the previously ignored substance, it cannot be made entirely out of the waste material. Other researchers have attempted to make 100% lignin carbon fibre, but this is too weak to use in cars and planes.
As a result, this carbon fibre uses some PAN with the lignin to produce a strong yet affordable and more environmentally friendly product, finding that 20-30% lignin is acceptable before strength begins to reduce.
“We wanted to combine the high strength of PAN with the low cost of the lignin to produce an automobile-grade carbon fiber,” said Jiang.
The researchers say their material could be used to make castings, tyre frames and internal car parts. However the next step will be to use it in a real-world setting within a car plant, in order to demonstrate its strength.
“If we can manage to get a fiber that can be used in the automobile industry, we will be in a good position to make biorefineries more economically viable, so they can sell what they usually would discard or burn,” said Ahring.
“And the products would be more sustainable and less expensive.”