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Lignin and cellulose create a strong bio-based carbon fibre

In order for Sweden to reach its climate goals and become fossil-free by 2045, a switch to lightweight materials in the transport sector is needed. Carbon fibre composite could replace steel, lowering the weight of a vehicle, but the carbon fibre that is commercially available today is primarily fossil-based and far too expensive to be a viable alternative to steel. This will not necessarily be the case in the future. RISE, Chalmers and KTH have partnered with Valmet and SCA to develop bio-based carbon fibre with promising mechanical properties from raw material harvested from Swedish forests.

The transport sector, which includes road traffic, shipping and aviation, currently accounts for a large percentage of greenhouse gas emissions. By lowering the weight of cars, trucks, boats and airplanes, emissions can be reduced, fuel economy can be improved and vehicle range (e.g. for an electric car) can be improved.

One way to reduce the weight of a vehicle is to replace steel with a lighter material with similar properties, such as carbon fibre composite. The problem is that the carbon fibre that is on the market today is manufactured from expensive, fossil-based raw materials.

– Commercial carbon fibre is expensive, which limits its use to advanced applications. The use of renewable raw materials can instead result in a cheaper, greener carbon fibre which opens the door to brand new applications, says Tobias Köhnke, project manager for LightFibre and Manager for Bio-based Fibres at RISE.

Mixture of lignin and cellulose

In the project LightFibre, RISE has developed a carbon fibre based on raw materials harvested from the Swedish forests. The development of bio-based carbon fibre is nothing new; research on the production of carbon fibre using lignin has been underway for a number of years. The challenge in the development of bio-based carbon fibre before has been creating a material strong enough to be viable for use in composite materials. But by mixing lignin with cellulose, scientists have come closer to the goal of producing a competitive bio-based carbon fibre with adequate mechanical properties at a reasonable price.

– This project has taken great strides in research and development towards achieving the necessary mechanical properties and process improvements required to produce a competitive lignin-based carbon fibre, says Henrik Linda R&D Manager at Valmet AB.

Carbon fibre from the pulp mill

Lignin and cellulose, which are found in large quantities in wood, are the starting point for production of the bio-based carbon fibre. Cellulose is produced in a (paper) pulp mill, and high quality Kraft lignin is extracted from the pulp mill’s black liquor through the LignoBoost© process developed by RISE and Chalmers which is now owned by Valmet AB. In the project, a method has been developed where Kraft lignin and cellulose are first wet spun into continuous fibres which are then converted into strong, bio-based carbon fibre.

The most significant effect of a cost-effective, carbon fibre based on forest raw materials will be increased use. From a Swedish perspective, it would be a tremendous benefit if a Swedish actor can secure a place in the value chain by converting forest raw material to carbon fibre, thus giving rise to a new Swedish industry, says Elisabeth Sjöholm, senior lecturer at RISE and senior researcher in LightFibre.


LightFibre

LightFibre is a three-year project collaboration between RISE, Chalmers, KTH, Valmet and SCA. In March 2019, the project presented two licentiate theses; Spinning of lignin-cellulose carbon fiber precursors byJenny Bengtsson and Carbon fibres from lignin-cellulose precursors by Andreas Bengtsson with Chalmers and KTH respectively. The project is financed by the Swedish Energy Agency.