Towards comparable life cycle assessments: Remodeling-based harmonization of polylactic acid waste depolymerization studies

As the use of polylactic acid (PLA) bioplastics grows, sustainable waste management options such as depolymerization become increasingly important. Evaluating its environmental impact relies on life cycle assessment (LCA), but differences in methodological choices (e.g., LCIA method), product system characteristics (e.g., geographical scope), and modeling environment (e.g., software) often lead to incomparable results. This study examined how such variations affect LCA results for PLA depolymerization through a two-stage approach, consisting of (i) a comparative assessment of all 9 life cycle inventory (LCI) datasets identified in the literature (from 6 studies up to December 2023), which revealed key inconsistencies such as insufficient process detail and data gaps on additives and catalysts, and (ii) a remodeling-based harmonization of the studies using consistent LCA parameters, addressing often overlooked factors including database choice, geographic location, and life cycle impact assessment (LCIA) method. The harmonized results show that the choice of LCI database significantly affects outcomes, especially regarding substitution products. Geographic differences related to energy mix also have notable impacts, while the LCIA method choice has minimal effect. The harmonized global warming potential (GWP) of PLA depolymerization ranges from −2869 to −1378 kg CO₂-eq per megagram (Mg, 1000 kg) of PLA waste. This remodeling-based harmonization can be applied across different fields to improve the consistency and comparability of LCA studies, enabling assessments that can reflect the actual performance of different product systems. The findings highlight the need for transparency in LCA assumptions; therefore, we provide recommendations to improve the reliability and reproducibility of future studies.