Research Questions Bioplastics’ Sustainability

March 1, 2021
New model points to carbon footprints exceeding previous estimates

A move to bioplastics use doesn’t necessarily lead to more climate protection, warn researchers at the University of Bonn in Germany. They found the sustainability of plant-based bioplastics depends largely on the country of origin, its trade relationships and the raw material being processed.

Agricultural engineers Neus Escobar and Wolfgang Britz from the Institute for Food and Resource Economics (ILR) and the Center for Development Research (ZEF) at Bonn updated the ILR and ZEF’s global economic model used to simulate the impact of rising supplies of bioplastics based on information from the Global Trade Analysis Project (GTAP), a worldwide network of researchers and policy makers conducting quantitative analysis of international policy issues coordinated by Purdue University, West Lafayette, Indiana.

The researchers first modified the earlier model by disaggregating both conventional plastics and bioplastics, as well as crops such as maize and cassava.

“This is crucial to better represent the bioplastics supply chain in major producing regions and assess their environmental impacts from a lifecycle perspective,” explains Escobar.

Then, after introducing concepts inherent to optimizing circular economy networks such as waste acquisition, outsourced materials and end-of-life alternatives for waste to the model, it was able to represent how traditional processes can satisfy the demand for bulk chemicals. For example, it can compare open-cycle end-of-life alternatives such as landfill or incineration with circular counterparts such as plastic pyrolysis and the recovery and reuse of monomers produced this way.

The modified model identifies the most promising waste processing network for a particular substance, and also recognizes and highlights those that perform poorly. It can generate new transformation steps that may close process chains, too.

The model also considers different sources and forms of data uncertainty, e.g., in the cost of applying different technologies, or in the yields of the required transformation processes. It can include multiple optimization criteria such as profit maximization and environmental impact minimization.

The model investigated the world’s main producers of biodegradable and bio-based plastics, including the European Union (EU), the United States, Brazil, China and growing prospect, Thailand. It simulated 36 different scenarios for each region.

“We found that the carbon footprints of commercially available bioplastics are much larger than the values previously estimated in scientific literature and policy reports,” notes Escobar. Carbon dioxide (CO2) emissions from changes in land use outweigh the greenhouse gas savings resulting from replacing fossil raw materials in the long term.

However, Thailand-produced bioplastics were found to save an average of 2 kg CO2/t of product. This, say the researchers, mainly stems from the relatively smaller increase in bioplastics production simulated, which translates into minor adjustments in food prices and associated land cover changes. Increasing bioplastics production from cassava and sugarcane in Thailand to match other regions can result in the loss of the country’s carbon-rich ecosystems.

The overall calculations show no particular region is clearly better positioned than another to become a hub for sustainable bioplastics production. More details are described in a recent article in Resources, Conservation & Recycling.

Chinese bioplastics likely has the largest land footprints, while the EU has the largest average carbon footprint: bioplastics produced there take an average of 232.5 years to offset global CO2 emissions. U.S.-based bioplastics production causes the greatest land and carbon spillovers, i.e., generating greater agricultural land expansion, deforestation and carbon emissions in the rest of the world than within the country. Bioplastics production in Thailand and Brazil comes at the cost of significant forest cover loss, which may impair biodiversity.

“Our study shows that an expansion in bio-based production should be carefully assessed on a region-by-region case in order to understand potential sustainability risks and trade-offs,” concludes Escobar.

The researchers emphasize that the proposed metrics can be used in the future to monitor the long-term sustainability of bioeconomic interventions globally. Among other things, they add, the metrics could help identify where complementary policies are needed — e.g., to prevent deforestation.

Seán Ottewell is Chemical Processing's editor at large. You can email him at [email protected].

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