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Materials Flow Analysis: Supporting a Circular Plastics Economy

Ginny Lee | January 22, 2021
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Plastics have become a significant material in many sectors but have contributed to a detrimental amount of environmental degradation. With current consumption patterns, continued plastic production will increase oil use. A report from the Ellen MacArthur Foundation even predicts that the world’s oceans will contain more plastic than fish by 2050. Even with today’s limited recycling, plastic use has largely been unsustainable as only about 9% of plastic waste is recycled.

To find potential solutions to global use and accumulation of plastic, the Program on Plastics, Ecosystems, and Public Health (PEPH) at the Institute for Sustainability and Energy at Northwestern University (ISEN) prioritizes the examination of the entire lifecycle of plastics. PEPH also leverages research on the impact of plastic waste on ecosystems and public health and the development of environmentally benign substitute materials. As part of their initiative to explore the implications of everyday plastic use, PEPH hosts a webinar series which brings together collaborators from academic, civic, NGO, and industrial partner institutions.

As part of this series, on December 10, Jennifer Dunn, Research Associate Professor of Chemical and Biological Engineering at Northwestern, presented research findings in a virtual seminar titled “Materials Flow Analysis in Support of Circular Plastics Economy Development: Polyurethane in the United States.”

The current plastics economy tends to follow a linear flow rather than a circular flow, which means that much of the plastic we dispose of ends up in landfills rather than being reused or repurposed sustainably. With China no longer accepting global plastic imports for recycling as stated in the country’s 2018 National Sword Policy, the value of plastic waste has decreased, which has resulted in an increase in diversion of plastic materials to landfills.

Dunn’s research focused on analyzing how polyurethane flows through the economy in favor of supporting a circular and more sustainable plastic flow. Her goal is to increase plastic recyclability rather than a linear flow that often leads to landfills and incineration.

Polyurethane is a type of polymer that is ranked 6th in worldwide production. Therefore, this material is used in many products and applications such as in foams, electronics, and adhesives. The versatility and widespread use of this material creates a unique challenge in analyzing its pathway. “I kind of view polyurethane as a challenge case for recycling and for increasing bio-based content because it has so many formulations and applications,” stated Dunn.

Although polyurethane has been useful in a wide array of products and applications, it poses multiple sustainability challenges. The production of the material itself requires fossil fuels, isocyanates, and polyols. Isocyanates are powerful irritants while polyols are compounds that make up resins that can cause slight irritation to the eyes and skin. Isocyanates especially are physically dangerous to humans because they irritate mucous membranes in the eyes as well gastrointestinal and respiratory tracts. However, they are only highly regulated in Europe. 

According to Dunn, when disposed of, about 30% of polyurethanes ends up in landfills. 40% is incinerated, which releases toxins and greenhouse gas emissions into the atmosphere, contributing to air pollution, and creates toxic byproducts such as bottom ash. Though the remaining 30% is recycled, there is a limited market for recycled polyurethane goods and such products often hold low economic value.

Polyurethane also has a long product lifetime. Though the period of decomposition depends on the structure and type of polyurethane, some polyurethane products can take up to 1,000 years to fully decompose. This means that even though such substances have been increasingly banned or phased out over the years, polyurethane materials from as far back as the 1950s, when polyurethane became commercially available, remain in landfills and continue to flow into today’s post-consumer waste cycle.

“We want to take the design process all the way back to the beginning—how can we design that polymer to be inherently recycled and incorporate bio-based material up to 50%?” said Dunn regarding addressing the challenges of recycling polyurethane. Dunn also stressed the importance of being able to account for any additional degradation that may occur in air and water.

To build a cohesive data flow analysis for polyurethane, Dunn’s team gathered data from governmental databases, literature, market reports, and industrial experts. Information on polyurethane waste streams, trades, and stocks were also observed from various industries.

From this analysis, Dunn’s team concluded that the most commonly recycled form of polyurethane is post-industrial carpet underlayment, which is a type of flexible foam. With more research, Dunn stated that carpet underlayment is a good target for maximizing recyclability of polyurethane, as this is today’s most dominant recycled polyurethane product and can therefore play an important role in learning how to enhance the circularity of the plastics economy.

The research further exhibits the potential for chemical recycling to become the ultimate recycling option in the United States. Currently, rebonding or mechanical recycling, a process that involves adhering small foam particles back together, is the primary recycling method that operates on a commercial scale in the United States.

The material flow analysis conducted by Dunn’s team is a quantitative tool for evaluating how bio-based materials can impact end-use markets and the environment. This research plays an essential role in discovering any limitations within the current material flow system as well as supporting the development of a circular economy.

The next stage of Dunn’s research will involve the analysis of economics and life cycle environmental impacts of individual pathways. During the seminar, Dunn stated that test cases were being chosen for this next phase of research, which is set to begin this January.

PEPH will continue to host informative virtual seminars throughout the year to continue this series, bringing together collaborators from a wide range of industries to address the implications and solutions of everyday plastic use.