University of Houston granted $4m to pursue waste polyolefins research

Planned projects include developing compatibilizers, advancing upcycling and boosting degradability

The University of Houston has received a $4 million grant to expand its research into the recycling and upcycling of polyolefins into useful end products. The funds will be supplied over a four-year period from The Welch Foundation, a Houston-based private funding source for basic chemical research.

The project is led by Dr. Megan L. Robertson, a professor of chemical and biomolecular engineering who has been a faculty member at UH since 2010. In a Sept. 27 phone interview, Robertson said that she will lead a team of 6 faculty members, including Dr. Alamgir Karim and Dr. Ramanan Krishnamoorti from chemical and biomolecular engineering and Dr. Brad Carrow, Dr. Olafs Daugulis, and Dr. Maurice Brookhart from chemistry, to work on the project, along with more than 20 students and post-doctoral researchers. The team will also partner with the newly formed Energy Transition Research Institute at UH, for which circular plastics is a key area of focus.

She explained that their efforts will focus on three areas of research for increasing the repurposing value of these very stable molecules:

• Compatibilization
• Upcycling
• Degradability

Robertson said the team is focusing on polyolefins, and particularly polyethylenes and polypropylene, due to the high use of those materials and their overall low recycling rates. Even HDPE, which is accepted by most recycling programs nationwide, is only recycled at a rate of 9-10 percent. New solutions are required to increase recycling rates of these materials, she says, due inherent limitations in traditional mechanical recycling processes.

Goal 1: Better compatibilization

Robertson knows about compatibilization, as she did her Ph.D. thesis on the topic at the University of California at Berkeley in 2006. She notes that many waste sorting programs do a good job at generating fairly pure waste streams, but the sorting process can be time-consuming and expensive. Compatibilizers, which are molecules that help mix disparate plastics that do not naturally want to do so, can reduce demands for sorting in the recycling process. However, the intake of mixed plastic waste at recycling facilities can vary widely in composition, and this can make it challenging to design compatibilizers that can consistently yield recycled plastic mixtures with good mechanical and performance properties.

While acknowledging that many are working on this challenge, she stated: “We are working on a modular approach, in which we could provide a library of different compatibilizers that can be used depending on the composition of waste plastics entering the facility that day.” Ideally, accomplishing this might also allow recyclers to be able to avoid the expensive sorting process by simply adding the appropriate compatibilizer to the waste stream they are processing. This technology is enabled by advances in olefin catalysis from the chemistry faculty on the team.

Goal 2: Upcycling via thermoset technology

The second focus of their research is on upcycling, or the converting of single-use plastic waste into something that can be part of a durable application with a long lifetime, such as insulating foams, coatings, furniture or infrastructure materials. To do this, Robertson’s team is converting polyolefins into thermosets, particularly polyurethanes.

They achieve this by functionalizing the heated material as it runs through a melt mixing or a high-shear extrusion process, without using any solvents. By creating polyols, the waste thermoplastic is then transformed into a thermoset that can be used in longer-term, more value-added applications.

Goal 3: Advance polyolefin degradability

Finally, the UH team plans to investigate how to make the highly stable polyolefin polymers more easily degradable, since it is very energy-intensive to break them down via chemical recycling. “Creating degradable polyolefins that still retain their needed properties will enable a circular strategy for reuse of the materials over many cycles,” she noted.

All told, Robertson says that she and her team’s overall objective is to use chemical functionalization strategies as a platform to convert recycled polyolefins to useful products and materials.