(82b) Unveiling the Truth: Energy-Environment-Economic (3E) Assessment on Sustainability of Bioplastics and Recycling

Are bioplastics sustainable? The empirical evidence surrounding this debate abounds, but the answer is inconclusive. Comparability among the studies has been the issue.

This paper presents an unprecedented energy, environment, and economic (³E) assessment of 16 studies on the life cycle and techno-economic assessments of bioplastics. All end-of-life scenarios were evaluated including landfill, incineration, composting, mechanical recycling, and chemical recycling. For benchmark, ³E factors of petroleum-based plastics were compiled. The research answers the question by concentrating on three factors, namely non-renewable energy use in MJ/kg-plastic (energy), global warming potential in kg-CO₂e/kg-plastic (environment), and profitability in US$/kg-plastic (economic).

It was revealed that comparable outcomes can only be achieved when careful categorization is applied to sensitive elements such as database, methodology, biogenic carbon uptake, methane release during biodegradation, production scale, and capability of recycled plastic to substitute virgin plastic. From these revelations, we proposed a novel standardization method in this study. Sixteen existing studies in literature were carefully selected based on similar database and methodology of life cycle and techno-economic analyses. Then, we performed regression and cost-benefit analyses to reliably identify new trends and compare ³E factors of different processes.

Following our proposed novel standardization protocol, the ³E assessment demonstrated that bioplastics are sustainable only under specific conditions. When biogenic carbon is accounted for and no methane is released during biodegradation, the life cycle of bioplastics showed significantly lower global warming potential. Lower non-renewable energy use was found in production of bio-based plastics with average value of 39 MJ/kg-plastic, while average value for petroleum-based plastics is 80.2 MJ/kg-plastic. Regression analysis in this study revealed that inclusion of biogenic carbon uptake reduces the global warming potential of bioplastics by 2.1 kg-CO₂e/kg-plastic, and a linear correlation can be observed where global warming potential increases linearly with non-renewable energy use. In terms of economic performance, as the average costs of lignocellulosic biomass (US$0.8/kg) is lower than polyethylene (US$1.7/kg), it is profitable to produce lignocellulosic-based plastic with strong polymeric linkages without major alteration.

Recycling was deemed the most sustainable plastic disposal method in all three factors. Compared to direct energy recovery (incineration), recycling of 100,000 ton-plastic/year resulted in reduction of non-renewable energy use by 51.0-63.0 MJ/kg-plastic, reduction of global warming potential by 3.2-3.8 kg-CO₂e/kg-plastic and increase in profitability by US$237.0-330.3/kg-plastic. It was also found that recycling was highly affected by production scale. When production scale decreases from 100,000 to 40,000 tons-plastic/year, the profitability decreases from 403.6 to 75.9 US$/ton-plastic. However, it is important to note that most existing studies in literature assumed that recycled plastics can substitute virgin plastic. In reality, mechanically recycled plastics often have lower quality than virgin plastics. Furthermore, applications of recycling are currently hindered by technological limitations. Automatic sorting and efficient logistics for waste collection are necessary to achieve continuous and sustainable recycling.

It is hoped that the standardization method developed in this study not only enables reliable ³E comparison of existing literature data, but also provides a guideline for future assessments on bioplastics. However, this method has a limitation as it only considers the ³E factors. It is suggested that future research consider factors such as eutrophication and land use requirements for bioplastics to obtain a more comprehensive sustainability evaluation.