Life cycle assessment of lignin-based carbon fibres

As vehicle manufacturers attempt to decrease the weight of their products, and consequently the fuel consumption during the use phase, carbon fibre reinforced polymers, CFRPs, are becoming more common. However, as the carbon fibre production route has proven to be very energy intensive, CFRP may not perform as well as conventional materials such as steel when using an environmental life cycle perspective. Carbon fibres are usually made from polyacrylonitrile, PAN, a fossil-based polymer. Research has shown that a possible route to reduce the environmental impact from carbon fibres is to replace PAN with a bio-based alternative, such as lignin. Lignin is a main by-product of many biorefinery processes that use ligno-cellulosic material as feedstock. A switch to lignin instead of PAN could reduce the environmental impact of the carbon fibres, decrease the dependence on oil as well as reduce the cost of the carbon fibres. This paper, which is a part of Frida Hermansson PhD-project will include findings from the life cycle assessment of lignin-based carbon fibres as well as discuss how different allocation methods will have effect on the final results. The production of lignin-based carbon fibres was assessed using life cycle assessment. The functional unit was 1 kg of carbon fibres at the factory gate. Results show that replacing PAN with lignin as a precursor fibre material could decrease the energy consumption as well as climate impact. However, as lignin is bio-based, land use will increase. The impact results for the lignin-based carbon fibres largely depend on how much of the environmental impact is allocated to lignin for a given biorefinery process. Lignin’s relatively low price in combination with its large quantity leads to the economic allocation method being the most favourable. Lignin has long been considered a waste product, but as the demand for lignin increases so should the price. This means that the type of allocation applied will have significant influence on the environmental impacts of lignin-based carbon fibres.