Nanocelluloses as sustainable emerging technologies: State of the art and future challenges based on life cycle assessment

Cellulose nanomaterials (CNs) are valuable, emerging green materials distinguished by their exceptional properties and a broad spectrum of potential applications in traditional and innovative fields. These nanomaterials exhibit high mechanical strength, a high aspect ratio, transparency, and a highly reactive chemical surface area. Additionally, they are biodegradable and produced from cellulose, an abundant and renewable resource. Such attributes position CNs as promising candidates in the rapidly growing sector of sustainable materials. However, like other nanomaterials in the developmental stage, the production, use, and end-of-life (EoL) management of these materials raise environmental, economic, and social concerns that need addressing. Emphasizing ecodesign and sustainable processes is crucial, particularly because the technologies for producing CNs are predominantly in the early to intermediate stages of technological maturity, as indicated by their low Technology Readiness Levels (TRL). Recognizing these challenges, this tutorial review aims to analyze the life cycle and environmental implications of CNs to enhance their ecodesign, an increasingly critical aspect of these emerging materials. To achieve this, a comprehensive review of peer-reviewed literature on the production processes and life cycle assessments (LCA) of CNs was conducted. This review systematically and thoroughly evaluates the environmental effects associated with various raw materials, processes, and applications from a life cycle perspective. By highlighting how methodological decisions can influence LCA outcomes, the review pinpoints critical impact areas and evaluates the environmental performance of CNs compared to alternative materials. Additionally, the review brings to light the main challenges, and identifies opportunities within LCA studies on CNs. A SWOT (strengths, weaknesses, opportunities, and threats) analysis was utilized to gather insights into the significance of integrating LCA in CN research for informed decision-making. This analysis has identified research opportunities, particularly in multi-product processes, multiple CN-based products, consequential modeling, and their end-oflife considerations. Future challenges include the need for primary company data, toxicity data for LCA, prospective LCA, and a multidisciplinary team with LCA expertise to address these issues. Drawing from the SWOT analysis, this review suggests a strategic framework to guide future LCA research on CNs, intending to improve their eco-friendly design and support the worldwide bioeconomy.