Creating Plastics With a Purpose

Most places now have prominent recycling bins for glass, paper and plastic. The problem is that almost none of that plastic actually gets recycled. A 2022 Greenpeace report found that, at most, only 5% of plastic gets recycled (a percentage that continues to drop). The remainder ends up in landfills or incinerators to keep the rest of your trash company. While some may vilify the prevalent use of plastics, these materials provide enormous benefits to society in food preservation, water filtration and health care. The reason so much of it goes unrecycled comes down to the disparate chemical components of various plastics, which currently cannot be recycled together. Additionally, the loss of performance of the materials that occurs during recycling means they often cannot be repurposed into the same products that they started in.

Megan Robertson, a professor in the University of Houston Cullen College of Engineering, is leading a research team to address these challenges. With a $4 million grant from the Welch Foundation, she and her team of six faculty members, including professors Alamgir Karim and Ramanan Krishnamoorti from the Department of Chemical and Biomolecular Engineering, and professors Brad Carrow, Olafs Daugulis and Maurice Brookhart from the Department of Chemistry, will collaborate on the project, along with more than 20 students and post-doctoral researchers. Their mission? To develop new chemical paradigms that will revolutionize our approach to recycling.

Robertson and her team have identified polymer molecules that can be added to the plastic waste as needed, allowing diverse plastics to be recycled together, without the need to separate them.

The project, titled “Enabling Polyolefin Circularity Via Chemical Functionalization, Compatibilization, and Upcycling,” embarks on three separate efforts that Robertson and her team expect will enhance recycling practices without losing the very properties that make plastics so beneficial.

“We know there are numerous benefits of plastics and what they do for society, but we need to address their limitations in a way that’s better for the environment,” Robertson says. In particular, the team will focus on a class of plastics called polyolefins, such as polyethylenes and polypropylenes, which represent more than 60% of all U.S. plastics but have dismal recycling rates.

Compatibilization

The first goal is to tackle the issue of compatibilization. As Robertson explains, the current plastic recycling process involves heating the material until it becomes liquid, then reforming and cooling it in pellets ready for the manufacturing pipeline. But first, recycling centers must sort the plastics based on molecular composition. Otherwise, the different plastics won’t mix—much like oil and water—unless a stabilizing agent is added. Robertson and her team have identified polymer molecules that can be added to the plastic waste as needed, allowing diverse plastics to be recycled together, without the need to separate them.

“On any given day, recycling facilities don’t know what they’ll be dealing with. Having modular compatibilzers that can be mixed and matched as needed to the types of plastics coming into the recycling facility would keep the process moving without the extensive sorting that is required currently,” she says.

Upcycling

The second focus of their research is on upcycling: converting single-use plastic waste into long-lasting, value-added products, thus extending their lifespan outside of landfills. To do this, Robertson’s team is working to convert plastics into thermosets, particularly polyurethanes used in insulating foams, coatings, furniture and infrastructure materials.

“What we’re trying to do is make the plastic more functional by running it through a commercially-relevant process involving extrusion that turns the plastic into a thermoset. This type of thermoset is used for durable products that have a longer life and greater consumer value than the types of plastics used for food packaging, as an example, which end up in landfills much faster,” Robertson says.

Degradability

A more recent approach, called chemical recycling, breaks the plastics down into monomers (the building blocks of polymers), which can then be used to make the polymers again. This is a circular process, as the same polymer can be broken and reformed many times over. Because polyolefins are highly stable, they are very energy-intensive to break down chemically, which, as Robertson notes, makes it difficult to apply chemical recycling processes to these types of polymers.

Their plan, simply stated, is to create degradable polyolefins that retain their original qualities and functionality, but that can be recycled and reused through this chemical recycling approach.

“Think of it like a loop: instead of making plastic, using it and then trashing it, instead we can create a circular economy aimed to keep the same plastic in circulation for as long as possible while simultaneously retaining its value and avoiding chemical leakage into the environment,” Robertson says.

In total, Robertson and her team plan to introduce these three approaches to enhance current recycling practices and envision a future in which plastic waste is converted into useful products and kept out of landfills.