Product System Realism in the Circular Economy: The Role of Stakeholder Decisions

Circular economy research and policy increasingly promote strategies such as recycling, reuse, repair, and design for circularity, yet implementation continues to fall short of ambition, as reflected in the decline of the global circularity rate from 9.1% in 2018 to 6.9% in 2025. A central reason for this gap is that circularity is often assessed through generic representations of product systems that do not adequately reflect how products are actually designed, used, collected, and managed in specific geographical and temporal contexts. This matters because the feasibility and environmental performance of circular strategies are context-dependent and shaped by stakeholder decisions across the product system.

The thesis is built around three connected concepts. First, circular economy transitions provide the normative and policy rationale by defining the direction of change. Second, stakeholder-informed product-system definitions explain how these transitions are shaped in practice, since stakeholders influence design, use, collection, and end-of-life pathways across specific contexts. Third, Life Cycle Assessment (LCA) provides the quantitative framework for evaluating the potential environmental impacts of these stakeholder-shaped product systems. Together, these concepts form the analytical foundation of the thesis.

The overall aim of the thesis is to improve the realism and decision relevance of circular economy assessment by integrating context-sensitive empirical evidence from stakeholders into product-system definition and LCA. It addresses three research questions:

RQ1: How can empirical methods generate context-sensitive data for product-system definition by capturing stakeholder-shaped system conditions?

RQ2: How can such context-sensitive data improve the understanding of product-system circularity?

RQ3: How can context-sensitive data on product systems be systematically integrated into LCA modelling?

To address these questions, the thesis applies two empirical methods, waste characterization and stakeholder interviews, in two contrasting case studies: cosmetic and personal hygiene primary plastic packaging returned through a retailer-managed take-back system in Denmark, and on-grid crystalline-silicon photovoltaic panels used in Denmark, with particular attention to end-of-life pathways extending beyond Europe, using Kenya as an illustrative case. These systems were selected because they represent very different circularity challenges: a short-lived consumer product with rapid material turnover and near-term policy relevance, and a long-lived, technologically complex infrastructure product whose end-of-life is separated by decades from its design and installation.

The thesis shows that circularity is not an intrinsic property of products alone, but an outcome of how stakeholder decisions interact with material characteristics, infrastructures, governance arrangements, and user practices in specific contexts. In the cosmetic packaging case, waste characterization revealed that the returned stream was not a homogeneous plastic fraction, but a heterogeneous and stakeholder-shaped stream containing non-target items, missing components, problematic color choices, and substantial residual product content. These findings challenged simplified assumptions about recyclability and showed that packaging circularity depends on the interaction between packaging design, product formulation, return behavior, collection-system configuration, and sorting conditions. In the photovoltaic case, stakeholder interviews showed that circularity is shaped by fragmented life-cycle geographies, formalized but incomplete circularity in Denmark, and highly variable end-of-life pathways beyond Europe, including reuse, hibernation, informal repair, storage, and disposal.

A key methodological finding is that empirical method choice should follow the dominant uncertainty in the product system. Waste characterization is most appropriate when uncertainty concerns the physical condition of the waste stream, whereas stakeholder interviews are most useful when uncertainty concerns how the system functions across actors, institutions, and places. By strengthening the product-system definition, these methods also improve LCA in distinct but complementary ways. Waste characterization provides primary, quantitative, product-centered data that particularly strengthen the inventory phase by replacing generic assumptions with measured information on material composition, design features, and contamination. It also supports goal and scope definition by clarifying what physically enters end-of-life management. Stakeholder interviews provide broader systemic insight by revealing missing pathways, actor dependencies, governance gaps, and future developments, thereby strengthening system boundary definition, parameter selection, and scenario construction. Neither method is inherently superior; their value depends on the type of uncertainty being addressed.

Because most LCA studies remain largely literature-based and make limited effort to integrate stakeholder perspectives, despite broad recognition of their importance, the thesis advances stakeholder analysis as a bridge between stakeholder-informed knowledge and LCA. Stakeholder-informed LCA, grounded in stakeholder analysis, is proposed as a default starting point for assessing circular economy transitions. Even without primary data collection, it improves purely literature-based LCA by making actors, assumptions, missing pathways, and parameter choices more explicit. Where major uncertainties remain, especially regarding physical product characteristics or pathway configurations, this baseline should be complemented by waste characterization or stakeholder interviews. The stakeholder analysis framework has so far been developed and tested for the cosmetic packaging case and therefore requires further application across other product systems and policy contexts.

The thesis contributes at three levels. Conceptually, it reframes stakeholders as analytical enablers of product-system realism rather than actors who are merely consulted or managed. Methodologically, it compares two empirical methods as distinct evidential pathways for product-system definition, shows that their value depends on the type of uncertainty present, and advances stakeholder analysis as a structured integration approach. Empirically, it generates two novel context-specific datasets: a granular waste characterization of cosmetic primary plastic packaging returned through a retailer-managed take-back system in Denmark, and a structured stakeholder-based account of circularity barriers and end-of-life pathways for on-grid photovoltaic panels across Denmark and Kenya.

The findings are situated and case-based. They are grounded in two product systems and specific geographical contexts and should not be treated as universally transferable. The methods also have clear limits. Waste characterization captures the material outcomes of stakeholder decisions, but not the motivations or institutional conditions behind them. Stakeholder interviews provide interpretive and forward-looking insight, but cannot quantify physical waste characteristics or material-level barriers. Neither method resolves all uncertainties on its own, which is why the thesis argues for their complementary use within a broader stakeholder-informed LCA approach.

The implications are relevant for research, policy, and practice. For research, the thesis shows that product-system definition should be treated as a major analytical step rather than a preparatory formality, and that empirical method selection should follow the dominant source of uncertainty. For policymakers, it shows that circular economy targets cannot be meaningfully assessed without attention to infrastructure, actor coordination, and future system readiness. For industry and practitioners, it shows that returned products and waste streams provide evidence of how systems actually operate, and that circularity depends on conditions no single actor controls. Overall, the thesis argues that improving circular economy assessment does not primarily require more abstract modelling sophistication. It requires better empirical ways of understanding how product systems actually operate, where circularity is constrained, and which stakeholder-shaped conditions must change for circular strategies to become feasible in practice. Product-system realism is therefore a precondition for credible circular economy assessment.