Cellulose nanocrystals (CNC) are versatile nanomaterials of exceptional strength with many applications ranging from packaging to medical uses. While typically produced from Kraft pulp, novel experimental pathways have been developed to obtain CNC from by-products; however, their environmental impacts have not been assessed at a future industrial scale. In this article, a prospective life cycle assessment (pLCA) is conducted for CNC production in two routes coupling acetosolv pulping and acid hydrolysis, with alternative feedstocks: mango seed shells (MSS) and oil palm mesocarp fibers (OPMF). The study is conducted from cradle to gate for 1 kg CNC (solids, in suspension) and follows an adapted version of the "SIMPL" approach for scenario-based prospective life cycle inventory (pLCI) modeling, while incorporating a pLCI database for 2040 (based on the "premise" framework). Upscaling assumptions based on process calculations, extrapolation, and expert advice are integrated into scenarios with consistency checks. Impact assessment covers climate change, freshwater eutrophication, and fossil resource depletion. A current technology (2024) is compared with future (2040) scenarios with varying degrees of technological progress and climate policy ambition. The MSS route consistently outperforms the OPMF route, with climate change impacts of 18.9-79.6 kg CO2 eq (MSS) vs. 26.1-127.8 kg CO2 eq (OPMF). However, the MSS route shows higher impacts than Kraft pulp-CNC (11.2 kg CO2 eq), mainly due to energyintensive acetosolv solvent recovery. Drastic modifications to the pre-treatments are necessary for MSS-CNC to compete with Kraft pulp-CNC. Insights to reduce CNC impacts and recommendations for upscaling bioprocesses are provided.
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