Importance of Material, Product and System Analysis in Design for Plastic Circularity

Plastic, although recognised as a revolutionary material integral to various aspects of our lives, has emerged as a stark emblem of human environmental impact. Despite active calls and emerging policies supporting a transition to the circular economy to help mitigate climate change and resource depletion, the current state of plastic circularity remains far from satisfactory. In the past two decades, European plastic flows have continued, and will continue, to grow exponentially, with most waste directed towards incineration or landfilling. In the idealised concept of circular economy (CE), plastic waste is envisioned as a valuable resource that can substitute virgin primary materials if effectively recirculated back into production systems, potentially eliminating the demand for new raw primary materials. In this perspective, recycling has been promoted as a solution for transforming waste into a valuable secondary resource. However, the circular material use rate (CMUR) of all materials, which measures the share of materials replacing virgin primary material in production processes, is 12% in the European Union (EU). Nevertheless, this rate highlights the gap between the amount of recyclable plastic fed back in plastic production and the demand for primary resources. Considering the ever-increasing demand for plastic, this low rate indicates that a large amount of primary raw material for plastic production is still needed. As such, implementing the concept of the CE in plastics requires identifying and addressing the barriers to plastic circularity in order to shift from disposable plastic waste to valuable circular materials.

This PhD thesis aimed to evaluate and identify barriers and levers encountered in moving towards CE for plastics. The goal of conducting comprehensive analyses is to gain insights into whether or not we are advancing closer to achieving the overarching plastic circularity, i.e., reducing waste, keeping materials in circulation, and reducing reliance on fossil resources. The study seeks to provide a nuanced understanding of the current state of plastic circularity and pave the way for informed strategies to overcome barriers and accelerate progress towards achieving circularity goals in the plastic sector.

This research is structured into three analysis levels: system, product, and material. These analysis levels are identified as key layers within which plastic circularity practices must be investigated (Chapter 1). This includes the following four analyses:

1. Analysis of the organisation of the plastic value chain to implement initia-tives that promote plastic circularity, complying with the CE principles.

2. Analysis of the circularity of plastic products by examining their potential for recycling and their ability to substitute virgin materials once recycled.

3. Analysis of how material selection for plastic products influences plastic circularity, with a focus on identifying contaminants that may impede recycling efforts.

4. Analysis of circularity indicators to estimate the implementation of plastic circularity in EU27 from 2020 to 2050, comparing two scenarios that promote plastic circularity to a business-as-usual (BAU) approach.

The findings of this thesis comprehensively capture the various contexts, challenges, and intricacies linked to implementing plastic circularity at the system, product, and material levels. First, at the system level, the effectiveness of the plastic value chain in fostering circularity is analysed through a systematic qualitative framework (Chapter 4.1). The analysis of 54 initiatives underscored the necessity for coordinated waste management, enhanced stakeholder awareness, improved understanding of the end-market, and the need for policies to support the transition. This thesis then goes on to explore the role of design in plastic circularity at both the product and material scales to understand where and why failures occur when considering recycling as waste treatment. A recyclable product is defined as a product undergoing collection, sorting, reprocessing, and replacement of virgin resources in production (Chapter 4.2). Considering these steps independently or partially is found insufficient to assess plastic circularity. Thus, estimating the potential substitution values must account for quality and physical losses during the waste treatment processes from initial collection to finally being returned to market. Insights from this discussion highlight the need to bridge polymer science–which quantifies property changes in mixed plastic waste for use in new products–with environmental engineering to build models and assessment tools that prevent overestimating plastic circularity. Lastly, at the material level, the impact of inks printed on flexible plastic packaging during mechanical recycling is investigated (Chapter 4.3). The analysis revealed that the selection of inks does not hinder blown-film sample production. However, the pigment aggregation occurring upon degradation of the nitrocellulose binder, and the emission of volatile organic compounds from the polyurethane binder contribute to lowering the quality of the recycled material. The analysis identifies the two solvent-based inks as contaminating the recycled material by restricting the use of re-cycled materials in low requirements products, such as bin bags.

In addition to investigating plastic circularity at the system, product and material levels, this PhD research examines forecasted plastic circularity improvements of the European plastic flows between 2020 and 2050 (Chapter 4.4). The material flow analysis (MFA) provides a comprehensive perspective on large-scale plastic flows and allows for a discussion of societal implications (Chapter 5). Implementing an enhanced circular scenario that promotes CE principles to the system boundary of the MFA is projected to increase the CMUR from 14% in the BAU scenario to 42% in the most optimistic scenario by 2050. The MFA forecasts show that recycling rates will increase when improved waste management scenarios are implemented. However, the increasing plastic consumption might out-balance the implementation of plastic circularity.

This PhD research highlights the imperative to analyse plastic circularity through multiple lenses, first independently at the material, product and system levels and then by forecasting the EU plastic circularity in 2050. The results demonstrated that the future of plastic circularity relies on the ability of the plastic value chain to implement concerted efforts to implement a systemic change. Plastic should be designed and manufactured for durability and circularity, ensuring compatibility with effective waste management systems. In this way, plastics can serve continuously without compromising the integrity and utility of recycled materials. This thesis serves as a call for discussion to act, first to build upon drastic upstream measures (pre-consumption, e.g., reducing production and designing plastic for circularity) and then continue implementing downstream measures (post-consumption, e.g., effective collection and recycling).