Defining the Sustainability Threshold of Circularity: A Comparative Assessment of Plastic Recycling Pathways

This research study examines the potential conflict between increasing plastic recycling rates (SDG 12) and achieving global carbon reduction targets (SDG 13). Although plastic recycling is widely promoted as a key circular economy strategy, its climate performance depends strongly on the carbon intensity of the electricity systems supporting recycling processes, a relationship that has received limited comparative attention. Using a desktop-based comparative environmental assessment, this study analyzes peer-reviewed literature and industrial reports published between 2015 and 2025 to determine the energy requirements and lifecycle carbon emissions of different waste management methods, ranging from mechanical recycling to chemical and advanced recycling. Mechanical recycling exhibited the lowest environmental burden, with approximately 130 kg CO₂-eq/t and an energy demand of about 1.8 GJ/t, whereas chemical recycling required 12–32 GJ/t and generated approximately 739 kg CO₂-eq/t. “Advanced recycling” demonstrated potential net climate benefits (− 348 kg CO₂-eq/t) under favourable lifecycle assumptions and low-carbon electricity systems. By comparing countries with renewable-dominant and fossil-fuel-dependent electricity grids, the study identifies the “sustainability threshold,” at which recycling becomes more carbon-intensive than virgin plastic production. The proposed comparative sustainability-threshold framework provides a practical basis for selecting recycling technologies according to national energy-system characteristics. The findings herein offer evidence-based guidance for policymakers and industry to align circular economy strategies with climate mitigation objectives, ensuring resource recovery does not compromise global decarbonization.