Assessing the future environmental impact of lignin-based and recycled carbon fibres in composites using life cycle assessment

Sammanfattning: Carbon fibre reinforced polymers (CFRPs) are composite materials that are gaining attention for their lightweighting and strengthening properties in a wide range of applications. However, using them instead of conventional materials (such as steel or other composites) does not automatically lead to a decrease in life cycle climate impact or energy use. This is the result of the energy-intensive production of the carbon fibres. Two routes that could mitigate this problem are: 1) the use of lignin for carbon fibre production and 2) the use of recycled carbon fibres. This thesis assesses how these two routes could decrease the environmental impact of carbon fibres in composites, and how challenges connected to assessing these emerging technologies can be handled using life cycle assessment (LCA). The two routes were assessed by conducting a meta-analysis of earlier LCAs of CFRPs and lignin production and three different LCA case studies. Results show that both using lignin as a raw material and using recycled carbon fibres have good potential to decrease the environmental impact of CFRPs, making them more environmentally competitive than other materials. It was found that the transition from polyacrylonitrile (PAN) to lignin as a raw material has good potential to decrease the environmental impact of future carbon fibres. However, the extent of this potential depends on both internal factors, such as process development, and external factors, such as the development of the lignin market and the future energy supply system.