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1. Introduction Life cycle assessment is a powerful tool for quantifying the environmental impacts of products and services and is an essential part of product development. It can, for example, be used to identify hotspots to find ways to keep environmental impacts as small as possible. Assessing a product or service under development requires a prospective approach. A problem in prospective life cycle assessment (pLCA) is, however, the lack of data, which can lead to inconclusive results. The prospective context, however, also implies that there is still room for process changes and improvements [1]. This paper will present a work procedure for pLCA that grew out of a multi-year project aimed at developing lignin-based carbon fibres for composites (see LIBRE [2]). The intention with this contribution is to provide practitioners guidance on how LCAs in early stages of material development can be handled. 2. Method:The development ofa work procedure for pLCA When starting the LIBRE project, there were no data available for the production of the fibres, and efforts needed to be made to: 1) identify hotspots in the life cycle of carbon fibre composites to show the possible influence of transitioning to a lignin-based fibre, and 2) identify other important routes for decreasing the environmental impact of the composite. This was then done by developing a meta-analysis framework for using results found in available literature on LCAs of carbon fibre reinforced polymers (CFRP) and of lignin production. The results found in the literature were carefully extracted and recalculated to the same functional unit to enable comparisons between studies. The meta-analysis found that a shift to lignin could decrease the environmental impact of carbon fibre composites, but that this is heavily dependent on the allocation approach used to allocate the impacts between co-products at a mill where the lignin is produced. The meta-analysis also identified recycling and recovery of fibres as promising, but that this also is very dependent on how allocation is handled, in this case allocation between life cycles [3]. To explore the influence of the allocation approach for lignin production, allocation approaches found in literature were applied to a case study of the climate impact of lignin extracted from a Kraft pulp mill (see Hermansson et al. [4] for details). In addition, two new allocation approaches were developed: 1) considering the impacts from the lignin extraction process in a subdivision style approach, and 2) partitioning the impacts of the system between energy streams and material streams based on mass conversion, followed by either energy allocation (for energy streams) or mass allocation (for material streams). Results showed that the climate impact of the lignin is highly sensitive to the choice of allocation approach. As the intention was to apply the allocation approaches in a pLCA, they were assessed based on sensitivity to changes in demand for lignin, as this is an aspect of this specific system that could change much over time. The outcome was that many allocation approaches are sensitive to the temporal settings of the study, in particular with regard to prices and/or what is considered the main reason for lignin being extracted from the mill. The influence of allocation approaches in recycling of CFRP was also assessed in a case study. Different allocation approaches were redefined to handle the multiple outputs of both polymer and fibre from composite recycling. The redefined allocation approaches were applied to different fictitious recycling systems that employed different recycling methods. Results showed that the outcome of the assessment is highly dependent on the inherent incentives for recycling in the allocation approaches. For example: The cut- off approach provides no incentive to recycle the product, whereas the end-of-life recycling approach and the circular footprint formula (CFF) do. Recommendations were to, if possible, include both the end-of-life recycling approach and the cut-off approach as two extremes in pLCAs, as the result of the case study showed a large sensitivity to quality and demand for recycled carbon fibres. The CFF, which can be seen as a compromise between the two other allocation approaches but that is dependent on information on the supply and demand for secondary material and therefore challenging to apply in a prospective context, can then be avoided [5]. When different technology routes and allocation approaches had been identified, the findings were applied in a case study of carbon fibre composites in road vehicles (see Hermansson et al. [6]). The technology routes were assessed both separately and grouped into coherent scenarios, as it is likely that some technology development routes will happen simultaneously [7]. By assessing them separately, the individual routes that are most promising for decreasing the environmental impact of the system could be identified. By assessing them together, it was possible to assess under which overarching conditions in society, for example due to aspects related to legislation or R&D funding, the environmental impact would be reduced the most. The end-result, where carbon fibre composites reduced the vehicles’ environmental impact in almost all futures [6], should be seen as an indication of the possible future environmental impacts of the system under study and can provide guidance to technology development. 3. Results,Discussion, and Conclusions The work procedure that grew out of the work in the LIBRE project is visualized in Figure 1. The procedure proved useful for tackling the issue of lack of data in early stages of materials development and helped identifying key parameters in both the technical development and in the surrounding world that would have a large influence on the end result. Figure 1: The procedure for prospective life cycle assessment in materials development, which grew out of the context of assessing carbon-fibre composites Key findings include the usefulness of mining and extracting LCA results from available literature to identify the most important parameters in early stages of materials developments. They also include recommendations on how allocation should be handled for both multi-output processes and recycling systems in pLCAs, also including some new options for multi-output processes. While the procedure was initially used and developed for assessing CFRP, we argue that it is likely applicable to many emerging technologies, especially when the assessment of these face the same types of difficulties in terms of data availability and uncertainties regarding changes to, for example, market demand and prices. 4. References [1] Arvidsson, R., et al., Environmental Assessment of Emerging Technologies: Recommendations for Prospective LCA. Journal of Industrial Ecology, 2018. 22(6): p. 1286-1294. [2] LIBRE. LIBRE-Lignin Based Carbon Fibres for Composites. 2016 [cited 2018 9:th of november]; Available from: http://libre2020.eu. [3] Hermansson, F., M. Janssen, and M. Svanström, Prospective study of lignin-based and recycled carbon fibers in composites through meta-analysis of life cycle assessments. Journal of Cleaner Production, 2019. 223: p. 946-956. [4] Hermansson, F., M. Janssen, and M. Svanström, Allocation in life cycle assessment of lignin. The International Journal of Life Cycle Assessment, 2020. [5] Hermansson, F., et al., Allocation in recycling of composites - the case of life cycle assessment of products from carbon fiber composites. The International Journal of Life Cycle Assessment, 2022. 27(3): p. 419-432. [6] Hermansson, F., et al., Can carbon fiber composites have a lower environmental impact than fiberglass? Resources, Conservation and Recycling, 2022. 181: p. 106234. [7] Langkau, S. and M. Erdmann, Environmental impacts of the future supply of rare earths for magnet applications. Journal of Industrial Ecology, 2021. 25(4): p. 1034-1050. Acknowledgement - This project has received funding from the Bio Based Industries Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 720707 and Chalmers University of Technology - Energy Area of Advance (ECE profile) Transport Area of Advance.