Environmental and process implications of lignin-based rigid polyurethane foams for thermal insulation: a comparative life cycle assessment

Rigid polyurethane foam provides efficient thermal insulation, ideal for energy-saving applications in building construction. Typically derived from fossil-based polyols and diisocyanates, polyurethane is now being innovated with renewable alternatives like lignin, a byproduct of the pulp and paper industry, offering a potentially sustainable path to lower fossil dependency and enhance environmental performance. This study focuses on scaling up three lignin-based lab processes of rigid polyurethane foam synthesis to evaluate their energy consumption and industrial feasibility. The processes include: (1) direct lignin incorporation without modification, replacing 30wt.% of fossil polyols; (2) hydrolytic depolymerization of lignin, substituting 50wt.% of fossil polyols; and (3) oxypropylation of depolymerized lignin, allowing for complete replacement of fossil-based polyols. The scale-up of these lab processes involved the development of life cycle inventories (LCIs) to be implemented in the SimaPro® software, establishing system boundaries and enabling a cradle-to-gate life cycle assessment (LCA) to determine the comparative environmental impact of each process. The LCA approach was chosen to provide a comprehensive view of the production chain, capturing the environmental trade-offs between lignin-based and conventional fossil-based polyurethanes. LCA quantifies impacts, identifies bottlenecks, and sets intervention priorities, while a sensitivity analysis was conducted to extend this perspective by examining variations across key process parameters to assess their influence on sustainability outcomes. This approach supports a clearer roadmap toward more eco-friendly polyurethane production at industrial scale.