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Plastic Pollution: Re-thinking Degradation and Recycling

Grace Wade | July 1, 2019
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Of the 8.3 billion metric tons of plastics generated since 1950, 79 percent of it has ended up in landfills and ecosystems. That adds up to more than 6.5 billion tons of plastics left to persist for hundreds or thousands of years in waterways and on land. Linda Broadbelt, Northwestern University’s Associate Dean for Research at the McCormick School of Engineering and Applied Science and Sarah Rebecca Roland Professor of Chemical and Biological Engineering, is seeking alternate means of disposal for plastics.

Broadbelt, who has been teaching at Northwestern for almost 25 years, works in complex kinetics modeling. In other words, she looks at large networks of reactions and attempts to create a quantitative description so researchers can better understand how these complex reacting systems behave. The computational approaches that she develops and applies can be used to suggest chemical strategies for the purposeful degradation of plastics to recover fuels and chemicals or to explain what happens to plastics when they degrade due to environmental exposure.

Broadbelt is one of the collaborators on the Program on Plastics, Ecosystems, and Public Health, a new initiative at the Institute for Sustainability and Energy at Northwestern (ISEN). The Program aims to address and find scalable solutions to the problem of global use and accumulation of plastics. To do so, it takes a multidisciplinary approach, bringing together a network of researchers and professionals to focus on three intersecting research areas: material and product innovation; air, land and water ecosystem dynamics; and public health impacts.

Earlier in her career, Broadbelt looked at the thermal degradation of plastics. “We were looking into heating polymers and waste plastics up to high temperatures in the absence of oxygen to turn them into usable fuels and chemicals,” explains Broadbelt.

This is known as tertiary recycling. Whereas primary recycling would be, for example, reusing milk jugs and secondary recycling would be reusing the materials to create a new product for a less demanding application, tertiary recycling involves breaking down plastics into small molecules to create fuels and chemicals.

“I would like to take another look at tertiary recycling because the computational methods that we use to model these kinds of complex reaction systems have continued to improve over the years,” says Broadbelt. “I think we could make even greater headway on the topic now.”

According to Broadbelt, the recycling of plastics for fuel was a prominent topic in the early ‘90s, but due to the emergence of biomass conversion as a competing technology and the fall in the price of oil from petroleum refining, tertiary recycling of plastics became less relevant. Now, she believes that plastics are back in the public spotlight due to a new generation of people concerned over the preservation of the planet.

“I am always interested in working on research problems that students are very passionate about and leading the next generation of scientists needed to solve the next generation of problems,” says Broadbelt. “I think this program resonates with students.”

For her, the ISEN Program acts as a means for researchers passionate about plastics to come together in collaboration. With expertise in a variety of skills, these researchers are able to approach the plastics problem from all different angles.

“I appreciate that ISEN put together teams to tackle plastics,” says Broadbelt. “ISEN has been instrumental in introducing me to fellow researchers such as those at Argonne National Laboratory and elsewhere who are all thinking about solutions to the global plastics problem.”