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Plastics have become an essential part of our economy. They show the highest production growth of all bulk materials and are responsible for 4.5% of global Greenhouse gas (GHG) emissions. This thesis assesses strategies to reduce the GHG emissions and resource consumption of the plastics sector by creating a dynamic, long-term model of the global plastics sector and conducting a case study on waste management pathways for plastic bottles. The model projects a doubling of global plastic production by 2050 and more than a tripling by 2100, with an almost equivalent increase in CO2 emissions if we follow current trends. This thesis shows that both a bioeconomy and a circular economy (CE) strategy can reduce GHG emissions in the plastics sector but that they also have trade-offs. A pure bioeconomy strategy could lead to the sequestration of biogenic carbon (negative emissions) but would continue to rely on new primary resources. A pure CE strategy, in contrast, would still depend on fossil resources for new materials and could limit the potential of biogenic carbon sequestration in the long-term. This thesis introduces the concept of a circular bioeconomy (CBE) for plastics and investigates the concept’s role in European industry clusters. Together, the chapters demonstrate that a circular bioeconomy, which combines biomass use with circular economy strategies, presents a synergy between climate and circular economy targets. It could turn the plastics sector eventually into a net carbon sink while reducing the need for primary resources.

Integrated assessment models (IAM) study the interlinkages between human and natural systems and play a key role in assessing global strategies to reduce global warming. However, they largely neglect the role of materials and the circular economy. With the Plastics Integrated Assessment model (PLAIA), we included plastic production, use, and end-of-life in the IAM IMAGE. PLAIA models the global plastics sector and its impacts up to 2100 for 26 world regions, providing a long-term, dynamic perspective of the sector and its interactions with other socioeconomic and natural systems. This article summarizes the model structure, mathematical formulation, assumptions, and data sources. The model links the upstream chemical production with the downstream production of plastics, their use in different sectors, and their end of life. Therefore, PLAIA can assess material use and emission mitigation strategies throughout the whole life cycle in an IAM, including the impacts of the circular economy on mitigating climate change. PLAIA projects plastics demand, production pathways and specifies the annual plastic waste generation, collection, and the impact of waste management strategies. It shows the fossil and bio-based energy and carbon flows in product stocks, landfills, and the emissions in production and at the end of life. • We included plastics production, use, and waste management into an Integrated Assessment Model (IAM). • Our model PLAIA provides a long-term, dynamic perspective of the global plastics sector until 2100 and its interactions with other sectors and the environment. • PLAIA can assess the impact of material use and emission mitigation strategies throughout the whole life cycle of plastics.

Biomass is projected to play a key role in meeting global climate targets. To achieve a resource-efficient biomass use, European bioeconomy strategies increasingly consider the concept of a circular bioeconomy (CBE). We define the term CBE via a literature review and analyze the concept’s role in north-west European bioeconomy clusters through interviews. We identify strategies regarding the clusters’ feedstock and product focus, and investigate what role biorefineries, circular solutions, recycling and cascading play. Finally, we discuss gaps in CBE literature and the potential contributions of the CBE to sustainability. The analyzed bioeconomy clusters move towards a CBE by increasingly considering residues and wastes as a resource, developing integrated biorefineries and focusing more on material and high value applications of biomass. However, there is so far only little focus on the end-of-life of bio-based products, i.e. on circular product design, recycling and cascading. Key challenges for implementing circular strategies are policies and regulations, costs and the current small size of bio-based markets. Amongst the product sectors the interviewees identified as promising for the bioeconomy, plastics and construction & building materials have most recycling and cascading potential. While the CBE could contribute to improving the sustainability of the bioeconomy, the concept is not inherently sustainable and its potential trade-offs need to be addressed. Especially social aspects, cascading, circular product design, and aspects related to product use seem to be underrepresented in CBE literature, while the topics biorefinery, wastes and residues as well as waste management are significantly covered.