Gauging the flows

A recent assessment of material flows for various resins indicates a need for significant improvement in recovery and end-of-life processes to ensure a truly circular economy.

Graphic PET and polyolefin material flows

The graphic featured has been reprinted with permission from Chaudhari, U.S., Johnson, A.T., Reck, B.K., Handler, R.M., Thompson, V.S., Hartley, D.S., Young, W., D. and Shonnard, D., 2022. Material Flow Analysis and Life Cycle Assessment of Polyethylene Terephthalate and Polyolefin Plastics Supply Chains in the United States. ACS Sustainable Chemistry & Engineering, 10 (39), pp.13145-13155. DOI: 10.1021/acssuschemeng.2c04004. Copyright 2022 American Chemical Society.

Many large retailers and brands have goals to steadily increase their use of recycled content in plastics packaging in hopes of achieving a circular economy for those plastic products. These companies also have announced goals to ensure they design their products with recyclability in mind to achieve that circular economy.

Yet, is a circular economy for plastics achievable, and is it better than a linear economy for plastics?

Several researchers from Michigan Technological University (MTU) want to answer these questions. MTU researchers submitted a proposal to the Reducing Embodied-Energy And Decreasing Emissions (REMADE) Institute to study polyethylene terephthalate (PET) and polyolefin material flows to gauge whether a circular economy is achievable for these materials as well as learn about emissions and energy consumption levels from these materials. The REMADE Institute approved the proposal, and a few MTU researchers began a two-year study on this topic, with help from Resource Recycling Systems (RRS), Ann Arbor, Michigan, and a few other academic researchers and organizations.

The researchers completed phase one of the study in September and released a report titled “Material Flow Analysis and Life Cycle Assessment of Polyethylene Terephthalate and Polyolefin Plastics Supply Chains in the United States.” The report was published by Washington-based ACS Publications, which is a division of the American Chemical Society.

Report authors include Utkarsh S. Chaudhari of MTU, Anne T. Johnson of RRS, Barbara K. Reck of Yale University, Robert M. Handler of MTU, Vicki S. Thompson of the Idaho National Laboratory, Damon S. Hartley of the Idaho National Laboratory, Wendy Young of Chemstations Inc. and David Shonnard of MTU.

The report provides material flow and life cycle assessment data sets for polyethylene terephthalate (PET) and polyolefin polymers in the U.S. while also estimating total supply chain greenhouse gas (GHG) emissions and energy consumption. Polyolefins researched include high-density polyethylene (HDPE), polypropylene (PP), low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE).

Shonnard says phase one findings show where improvements need to be made to achieve a circular economy for plastics.

“We were able to develop a systems analysis of the entire U.S. plastics supply chain for these plastics,” he says. “Previous studies had looked at these and other plastics in a more limited sense, perhaps just for resin production, neglecting end-of-life processes. We assembled the whole system and conducted an analysis for these plastic types. … We have a better understanding of the nature of the plastic material we attempt to have a closed-loop system on.”

Circularity challenges

Mapping out material flows for PET and other polyolefins highlighted some gaps in the material flow system for some plastics.

When analyzing material flow value chains for plastics, Johnson of RRS says PET tends to have the healthiest recovered value chains. “PET is widely recognized as being recyclable by consumers,” she says. “Often, when it is collected, it finds a home. It is a valued commodity.”

Johnson adds that voluntary commitments from brands and retailers to use recycled content also have increased demand for PET.

“There’s a lot of market pull for this material,” she says. “Quite frankly, the bottleneck is the supply of PET is not sufficient to meet the demand out there for recycled content of the quality that’s needed.”

Although PET has many good end markets, Johnson says the same cannot be said for polyolefins.

While natural HDPE is in high demand for food-grade packaging, Johnson says colored HDPE has a harder time finding circular end markets. “A lot of HDPE is colored—like detergent bottles. But that material can’t go into food-contact packaging through mechanical recycling processes and is limited in other packaging applications due to its color. So, [colored HDPE] is typically put into plastic lumber, decking, pipe or other types of durable goods that we’re not likely to bring back into the system.”

Shonnard says LDPE and LLDPE have the most challenging material flows—the U.S. is producing more virgin LDPE and LLDPE by weight than it is of other resin types, but very little LDPE or LLDPE is recycled. According to the study, the U.S. produces about 12 million metric tons per year of virgin LDPE and LLDPE.

“What that tells us is to achieve a circular economy for films, we need to have different infrastructure to gather, collect and process them compared to what we have now,” Shonnard says.

Johnson adds that many programs focus on recycling packaging, but not as many work around ensuring nondurable and durable plastic goods ultimately are recycled.

“There’s a lot of focus on packaging,” she says. “While important, there’s opportunity that’s lost. We look at things like textiles. We have a lot of textiles that are principally polymer based. Today, we have no system to collect, sort or recycle [textiles]. We have a lot of durable goods out there. So, we need to be thinking forward as to what are the systems needed to bring those products back?”

Material complexity presents more challenges to the plastics supply chain, such as recycling multilayer plastic packaging. Shonnard says it’s possible to recycle multilayer plastic packaging, but it’s not nearly as economical as recycling monomaterial packaging.

Additionally, Shonnard says it is challenging to have consistent community engagement and consumer behavior around recycling PET and polyolefins across the U.S. He says, “Even if we have the infrastructure and great chemical recycling processes, if nobody puts stuff in the bin, it’s not going to work. We need to think beyond technical and engage with communities and policy to achieve greater levels of circularity.”

Addressing shortcomings

The first phase of MTU’s study highlights that work needs to be done to recover more plastics and reduce emissions and fossil energy usage tied to those materials.

“I think we’ve really lacked that system thinking when it comes to how we sustainably manage a class of materials like plastics,” Johnson says. “I think we need to step back and look at the entire material system and take a more comprehensive approach with policy and as we consider technology.”

Johnson adds that the study also stressed the need to apply various recycling collection and processing methods to achieve circularity for plastic supply chains.

“We have to have a much broader point of view on circular economy,” she says. “Mechanical recycling alone is not going to get us there. … We also need to be thinking about much different collection strategies. Textiles, for instance, have been one of the fastest growing categories of municipal waste for quite some time now, but we have paid zero attention to developing any sort of infrastructure to collect or reclaim them. There are industry initiatives working on that, but we don’t really see that translating into any municipal activity at scale.”

She continues, “If we aspire to have a circular economy for plastics or even packaging, we really need to be pretty committed to thinking about what are the policy interventions, incentives and education awareness needed to make the connection between these materials and those systems to recover them.”

This year, MTU researchers are conducting a second phase of this study, focused on assessing whether a circular economy for plastics offers better energy efficiencies than a linear economy. Shonnard says MTU hopes to publish findings from the second phase of the study by September 2023.

“We’re trying to accomplish as much as we can [with the study], but it’s a large, complex research question,” he says. “We can’t answer every question, but we want to take strides.”

The graphic featured has been reprinted with permission from Chaudhari, U.S., Johnson, A.T., Reck, B.K., Handler, R.M., Thompson, V.S., Hartley, D.S., Young, W., D. and Shonnard, D., 2022. Material Flow Analysis and Life Cycle Assessment of Polyethylene Terephthalate and Polyolefin Plastics Supply Chains in the United States. ACS Sustainable Chemistry & Engineering, 10 (39), pp.13145-13155. DOI: 10.1021/acssuschemeng.2c04004. Copyright 2022 American Chemical Society.

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