Revealing optimal end-of-life options for biodegradable plastic bags: A cradle-to-grave life cycle assessment

Growing environmental concerns over plastic waste and fossil fuel consumption have driven the exploration of sustainable alternatives such as biodegradable plastics. Previous studies mainly focused on the PBAT, PLA and their blends with different scope, data source, and EOL scenarios in different degradation conditions, which leads to the bias in the degradation rate of biodegradable plastics and environmental impact results. This study conducted a comparative life cycle assessment of commercial biodegradable plastic bags made from PLA/PBAT and PLA/PPC blends based on the localized life cycle inventory for biodegradable plastic in China. Four end-of-life (EOL) options including industrial composting, anaerobic digestion, incineration and landfill were considered to identify the optimal environmental performance of biodegradable plastic bags, and environmental performance of biodegradable plastic blended bags replacing conventional plastic bags in the express and takeaway industries were evaluated. Results revealed that PBAT/PLA/CaCO₃ plastic bags showed superior environmental performance across 10 impact categories compared to other blended biodegradable plastic bags (with reduction ranging from 8 % to 48 %), primarily evident in human toxicity (27 %-48 % reduction), ecotoxicity (35 %-40 % reduction), terrestrial acidification (36 %-39 % reduction) and marine eutrophication (24 %-27 % reduction). This advantage stems from the high inorganic filler content, which reduces the consumption of virgin petroleum polymers. In contrast, due to lower CO₂ emission and energy consumption in feedstock production, PLA/PPC plastic bags performed superior performance across other seven impact categories, such as ozone depletion (80 %-87 % reduction), ionizing radiation (22 %-25 % reduction) and global warming potential (22 %-26 % reduction). The cradle-to-grave GWP of PLA/PPC (70/30) plastic bags is 4.22 kg CO₂ eq per kg, 26 % lower than that of PBAT/PLA/CaCO₃ (67/3/30) plastic bags. Biodegradable plastic bags have better environmental performance in anaerobic digestion and incineration conditions, the worst in composting condition. Anaerobic digestion is the optimal EOL option for PPC/PLA plastic bags, offsetting 2 %-65 % of the cradle-to-gate environmental impact across 18 impact categories. Incineration is the optimal EOL option for PBAT/PLA plastic bags, offsetting 1 %-43 % of the cradle-to-gate environmental impact across 18 impact categories. The substitution of PVC bags with biodegradable plastic in the express industry has significant environmental gains, with impacts reduction ranging from 16 % to 97 % across 9 impact categories. Substituting HDPE bags with biodegradable alternatives in the takeaway industry has limited benefits, achieving emission reductions ranging from 3 to 96 % across only 5 impact categories. This study provides insights for green substitution and sustainability of biodegradable plastic packaging, and sustainable management of plastic packaging waste.