How multifunctionality modelling in LCA affects decision-making: The case of chemical recycling of plastic waste

Chemical recycling (CR) holds promise for closing the plastic loop, but demonstrating its environmental benefits is crucial for policy and economic support. Life cycle assessment (LCA) assesses environmental sustainability, yet variations in modelling, such as multifunctionality, complicate decision-making. This study contributes to LCA multifunctionality modelling theory by examining its effects on LCA outcomes. Using two CR plastic waste case studies, seven modelling approaches were analysed, varying the functional unit (product/waste perspective), co-product multifunctionality (substitution (Sub)/basket of products (BoP)), and end-of-life (EoL) multifunctionality (cut-off/circular footprint formula (CFF)). Results showed consistent impact deltas for BoP and Sub with well-defined boundaries and cut-off EoL when comparing CR's impact with conventional waste management and production systems. However, differences in absolute results and comparative metrics for Sub and BoP highlight the risk of misinterpretations. By demonstrating the influence of modelling choices, this study provides actionable insights for policymakers, industry, and researchers, enhancing informed LCA-based decision-making.