The laws of physics tell us that more work is required to accelerate a heavy object than a light one and, when it comes to cars, that means more fuel consumption and emissions. Novel processing technology is turning lignin into carbon fibre to reinforce tomorrow’s lightweight composites.
The automotive industry has made important strides in reducing the weight of vehicles by replacing heavy steel with plastics and composites. Common plastics are relatively ubiquitous but carbon fibre-reinforced ones – stronger materials that can even be used for structural components – are still quite expensive and primarily used in high-end sports cars and race cars. The EU-funded GreenLight project has developed a processing method to manufacture carbon fibre from lignin, an inexpensive by-product of the pulp and paper industry. Benefits abound for the paper and pulp industry, the automotive industry, and the environment.
Marginalising fossil fuels in more ways than one
The carbon fibre market is expected to grow from about USD 5 billion in 2019 to more than USD 13 billion in 2029, with automotive being the fastest-growing end-use industry in terms of value. About 90 % of carbon fibres are currently produced from the synthetic precursor polyacrylonitrile (PAN). PAN is derived from fossil fuels and producing carbon fibres from it is difficult and expensive. An eco-friendly alternative would reduce dependence on fossil fuels. Further, as project coordinator Ewellyn Capanema explains: “Cost-efficient biobased carbon fibres would enable an increased replacement of steel with carbon-fibre composites in cars. This would decrease the weight and fuel consumption of the car fleet, significantly reducing emissions.” Kraft lignin is a carbon-rich biopolymer produced during the kraft process converting wood into pulp. It can be isolated from pulp mill ‘black liquor’ (the by-product after cellulose fibres have been retrieved) in solid form. Unlike PAN, lignin can be processed via melt spinning, or melt-extruding, which is simpler and cheaper than PAN processing via solution spinning that also requires the use, removal, and recovery of organic solvents. However, large-scale melt-spinning methods to turn lignin into carbon fibre did not exist.
Let the spinning wheel turn
The team has filed a patent for their novel lignin spinning process that allows continuous spinning and winding with automatic spool change. “GreenLight has now demonstrated continuous multifilament spinning (about 1000 filaments) of softwood lignin produced from the kraft process. The resulting fibres have the highest tensile properties reported to date for melt-spun pure lignin-based carbon fibres, and the conversion process is faster than that previously reported. Based on their mechanical and surface properties, lignin-based carbon fibres could be used to manufacture short-fibre composites that have lower production costs and broad applications,” Capanema explains.
Plant-based car parts could be around the corner
Kraft lignin accounts for about 85 % of global lignin production and GreenLight’s technology can quickly and cost-effectively turn it into lignin-based carbon fibres. With the carbon fibre market predicted to nearly triple in the next decade, the forest and pulp and paper industries could have a substantial new market for lignin. The favourable outcomes of GreenLight’s techno-economic and life-cycle assessments support the financial and environmental benefits of lignin-based carbon fibre. As the GreenLight consortium moves toward commercialisation, plant-derived carbon fibre composites could be around the corner in tomorrow’s lightweight cars with small carbon footprints.