Circular Economy Sustainability Analysis Framework for Plastics: Application for Poly(ethylene Terephthalate) (PET)

The establishment of the circular economy (CE) for plastics aims to reduce material losses and dependence on virgin materials; however, this practice does not necessarily imply reduction of life-cycle impacts. In this study, a CE sustainability analysis framework combining life-cycle assessment (LCA) and material flow analysis (MFA) was developed to simultaneously evaluate the life-cycle impacts and circularity metrics of implementing different CE strategies of production of plastic packaging, using poly­(ethylene terephthalate) (PET) bottles as an example. The strategies included increasing the recycling rate of PET bottles and integrating two chemical recycling technologies in industrial development: enzymatic hydrolysis and methanolysis. The energy use of enzymatic hydrolysis and methanolysis was estimated to be 57 and 38 MJ/kg PET, respectively, while the two technologies accounted for greenhouse gas (GHG) emissions of 3.0 and 2.0 kg CO2 e/kg PET, respectively. The analysis at the system level demonstrated that compared to the current practice, relying on 97% virgin PET resin, the joint implementation of these strategies generated similar GHG emissions (3.2 kg CO2 e/kg bottle) but reduced virgin material use and solid waste generation by 56 and 64%, respectively. Based on present technology development, increasing the share of mechanically recycled resin in bottle manufacturing and using a decarbonized electricity grid resulted in 14 and 9% lower GHG emissions, respectively, than the current supply chain.