(46c) Guiding the Transition to a Sustainable and Resilient Circular Economy: An Eco-Inspired Quantitative Framework

Circular Economy (CE) presents an alternative business model to the prevailing business-as-usual economy. Unlike the linear consumption pattern of finite resources without product recovery at the end of their life, CE emphasizes closing the loop for products. This approach has the potential to tackle various environmental issues, including resource depletion, climate change, and biodiversity loss, by promoting the reuse, recycling, and regeneration of materials within the economy.

A considerable body of literature examines the potential of the CE and has developed indices and metrics to assess the level of circularity across different scales, ranging from product-level to industrial parks and the global economy. Product-level metrics, in particular, are extensively studied and are designed to measure the circularity of individual products within an economy. These product-level CE metrics serve as valuable tools for companies and other stakeholders to evaluate the circularity of their products and supply chains. By identifying the degree of circularity and pinpointing bottlenecks, these metrics can inform strategies to enhance the overall circularity of products and supply chains.

While existing metrics primarily emphasize circularity strategies centered around recovery rates based on material and energy flows, they often overlook other crucial aspects of Circular CE strategies. CE strategies extend beyond supply chain and technological interventions aimed at improving recovery rates of materials and products at the end-of-life stage. Changes in consumption patterns and business models also play a significant role in enhancing product circularity and facilitating the transition to a sustainable CE. Unlike strategies focused solely on product recovery, these approaches are often evaluated qualitatively. To our knowledge, there is currently no comprehensive systematic framework available to quantitatively assess the degree of circularity achieved through various CE strategies, including those targeting consumption patterns and business models.

Furthermore, alongside promoting circularity, CE strategies should also strive to foster a sustainable and resilient economy, which ultimately constitutes the overarching objective of CE. Achieving environmental and economic sustainability necessitates access to comprehensive information regarding material, energy, economic, and environmental flows. However, such detailed data is often lacking during the initial stages of designing a CE. This gap in information availability poses a challenge, and closing this gap is essential for enabling informed decision-making and enhancing the effectiveness of CE initiatives at an initial stage of a design.

Focusing solely on enhancing the circularity of a supply chain may inadvertently lead to network designs that lack resilience and flexibility. Therefore, it is crucial to incorporate resilience considerations into the evaluation of CE solutions to assess their robustness in the face of system shocks. A resilient CE should be able to withstand perturbations with minimal damage, highlighting the importance of capturing resilience in CE supply chains. While dynamic engineering resilience metrics have been utilized to assess the impact of perturbations on system survival, these methods require extensive static and dynamic information about the system, which may be lacking at the early design stage [1]. Hence, there is a need for a framework that can evaluate resilience at an early design stage based solely on product flow information. Such a framework would enable the assessment of CE solutions' resilience potential and inform decision-making processes to enhance the robustness of supply chain designs.

In this study, we aim to overcome the above-mentioned limitations of existing CE frameworks and address gaps in the literature by developing an ecologically inspired (eco-inspired) framework rooted in the principles of Ecological Network Analysis (ENA). This framework comprises three sets of metrics. The first focuses on capturing the circularity and resource efficiency achieved through CE strategies. These metrics align with conventional CE metrics, measuring factors such as product recovery rates at the end of life and virgin resource consumption rates. The second set of metrics assesses the sustainability and resilience of a CE system during the early design stages, utilizing physical flow network of products. Importantly, this set of metrics does not require detailed economic, environmental, or dynamic flow data. Lastly, the third set of metrics is designed to evaluate the effectiveness of various CE strategies, ranging from closed- and open-loop recycling to changes in consumption patterns such as product refusal. These metrics serve to guide the improvement of CE designs by informing decisions about adopting or modifying CE strategies.

We have defined the following metrics by tailoring their counterparts in ENA to suit the unique characteristics of product-level CE:

• Detritivory to herbivory ratio (D:H): This metric serves as a conventional circularity metric, reflecting the recovery rate within a product-level CE.
• Resource Consumption Efficiency (RCE): This metric measures the rate of resource consumption required to produce a certain quantity of product.
• Network Intensity (NI): NI quantifies the intensity of a network based on the flow quantities within it. It can be used as an initial tool to compare the environmental and economic intensity of different CE strategies.
• Robustness: Robustness, akin to ecological resilience, assesses the degree of order within a CE network. It gauges the network's ability to withstand shocks in the event of a disturbance.
• Loop Tightness: This metric evaluates the tightness of loops within a CE, favoring closed-loop recycling with tighter loops.
• Mean Circularity Level: Based on a CE hierarchy of different design strategies, this metric assigns scores to various CE strategies, with refusing (reducing consumption) being the most favorable and littering (waste disposal to the environment) the least favorable. It provides a holistic assessment, capturing not only product recovery strategies but also changes in consumption patterns or product design.

This framework was applied to a case study involving multi-layer plastic films utilized in Sheet Molding Compound Production (SMC film). SMCs are commonly employed in the manufacturing of bathtub products. SMC films are used for their carrier and barrier properties but result in a significant amount of waste annually. This waste presents a substantial opportunity for recovery and valorization at the end of their useful life.

In this study, we proposed several circularity strategies to promote the circularization of SMC films. These strategies include:

• Reuse: Mechanical and solvent-based recovery techniques are employed to clean the SMC film, allowing for its reuse in the same production process [2].
• Recycle: A solvent-based method is utilized to extract various polymer layers in the film and recycle the resin to produce new film [3].
• Downcycle: The film waste undergoes pelletization and injection molding processes to create other types of products. This approach represents an open-loop recovery, as the recovered material is not reintegrated into the same product system [2].
• Diverse End-of-Life (EoL): A combination of the previous three end-of-life alternatives is employed to treat the film waste. This scenario demonstrates the impact of utilizing a diverse set of EoL strategies on the robustness of a CE network.
• Refuse: This scenario considers CE strategies beyond EoL recovery to reduce the demand for SMC films. For example, changes in consumer behavior driven by environmental awareness can decrease SMC film consumption. Similarly, innovations in product design and business models, such as adopting in-mold coating technology [4] or implementing a product-as-a-service model [5] for bathtub products, can reduce the production and consumption of SMC films.

Using the eco-inspired framework, we conduct a comparative analysis and ranking of the circularity strategies based on their circularity, resilience, and sustainability. This framework facilitates the identification of bottlenecks in circularity, resilience, and sustainability, allowing for modifications to the CE strategies to achieve targets in all three areas. The results of the framework reveal that a combination of the refuse and diverse EoL strategies prove to be the most effective in meeting circularity, resilience, and sustainability targets. This scenario was identified as our best case scenario. Furthermore, by comparing the circularity, resilience, and greenhouse gas (GHG) emissions of the best case scenario with the business-as-usual linear economy for SMC films, significant improvements were observed. Specifically, there was a 77% improvement in circularity, a 51% enhancement in resilience, and a substantial 90% reduction in GHG emissions. These results highlight the practical application of the eco-inspired framework in designing circular, sustainable, and resilient solutions for a wide range of products. The framework offers valuable insights for designing CE strategies that achieve environmental, economic, and social sustainability goals.

Reference:

[1] Chatterjee, A., & Layton, A. (2020). Mimicking nature for resilient resource and infrastructure network design. Reliability Engineering & System Safety, 204, 107142.

[2] Nazemi, F. et al. (2024). Life cycle and circularity assessment of multilayer films used in Sheet Molding Compound Process (Under Preparation).

[3] Costamagna, M., Massaccesi, B. M., Mazzucco, D., Baricco, M. & Rizzi, P. Environmental assessment

of the recycling process for polyamides - Polyethylene multilayer packaging films. Sustainable Materials

and Technologies 35, e00562 (2023).

[4] Ko, S., Ouyang, X., Straus, E. J., Lee, L. J. & Castro, J. M. Processability study of in-mold coating for sheet molding compound compression molded parts. Polymer Engineering Science 59, 1688–1694(8 Aug. 2019).

[5] Tukker, A. Product services for a resource-efficient and circular economy – a review. Journal of Cleaner Production 97, 76–91 (2015).