Most scientific discovery is incremental: Breakthroughs happen after years and years of tiny steps.
But a recent University of Michigan discovery was a happy accident. It started with a disposal container and led to a $2 million Emerging Frontiers in Research and Innovation grant from the National Science Foundation to explore using adhesives to capture microplastics from wastewater.
Takunda Chazovachii, a graduate student in the lab of chemistry professor Anne McNeil, principal investigator of the grant, was working with high school student Edwin Zishiri, on a project to chemically repurpose vulcanized rubber from tires.
Zishiri threw some fine particles of rubber from tires into a liquid waste container Chazovachii uses to dispose of some adhesive he had been working with.
"It’s actually pretty annoying how sticky this material is, so I would just dissolve it in some solvent, swirl it and pour it in the liquid waste container,” Chazovachii said. "Then, as I was pouring it inside, I noticed the whole mixture was black, and I thought, ’I need to tell Edwin to dump solid stuff in the solid waste, not in the liquid waste.’”
He turned out the lights and went home. The next day, he came back, and instead of a black mixture in the liquid waste container, Chazovachii saw a black blob floating in the now clear solvent. He realized these tiny particles-ranging from just 20 microns (a human hair is 70 microns wide) to 300 microns in size-had clumped together on the adhesive. He snapped a photo of it.
The adhesive Chazovachii had tossed into the liquid waste container was synthesized during a different project aimed at reusing absorbent materials in diapers. He showed McNeil the photo he had snapped of the adhesive collecting the tiny tire particles and a lightbulb went on.
"When I saw it, I immediately recognized its potential for microplastics capture,” McNeil said. "It was a eureka moment.”
The grant builds on this aha moment by aiming to identify the best adhesives for removing microplastics from wastewater and diverting them from wastewater sludge. Ultimately, the researchers would like to engineer a device, outfitted with the ideal adhesive, that would be used in wastewater treatment plants to filter out these tiny plastic particles.
The majority of microplastics in wastewater are tiny fibers sloughed off from our clothes as they run through washing machines, but they also come from tires as they wear against roads and other fragmentation of larger plastic items. Different types of microplastics adhere to adhesives in different ways, McNeil says.
"Because adhesion is really a chemical interaction, there are certain properties of adhesives that will bind better. We’ll capture some microplastics better than others with a single adhesive,” she said. "There’s a lot of chemistry that’s going to go into designing either the best all-purpose adhesive, or engineering a multilayer device, with each layer having a different adhesive that’s optimized for a certain type of plastic.”
For example, she says, polyethylene, a type of plastic used in packaging, is composed of hydrogen and carbon bonds. The material is nonpolar-meaning atoms within the material share their electrons equally. What polyethylene will stick to is very different from what polyester, a material that composes much of the clothing we wear and that is very polar, will adhere to.
Co-principal investigator Paul Zimmerman, associate professor of chemistry, will help identify the best candidate materials for microplastic capture. He will do this by using simulations to study the specific interactions of small plastic particles with materials that capture the particles.
"There are a few possibilities for plastic capture mechanisms: for instance, dispersion across the surface or encapsulation,” Zimmerman said. "Which mechanism operates-this may depend on the type of plastic particle-will determine how effectively the binding occurs, and whether the plastic can be recovered for recycling.”
Zimmerman’s group uses atomistic simulation techniques that capture the full chemical behavior of binding, or how a bit of plastic will adhere to the material that captures it. This type of simulation allows the researchers to predict which materials will work best for different types of plastics directly from the simulation, without relying on the need to physically perform the experiments.
Co-principal investigator Brian Love will undertake engineering structures to capture these microplastics.
"Microplastics are actually captured relatively effectively at wastewater treatment plants and other distribution processing facilities that are capable of treating effluent runoff water, but the problem we see is that if the sludge is redeposited back on fields and streams, we’ve sort of shot ourselves in the foot,” said Love, professor of materials science and engineering, biomedical engineering, and macromolecular science and engineering.
"It would be nice to be thinking about tools and methods based on our own project that have the capacity to perhaps redirect those microplastic particles in a different direction.”
Love’s contribution will include designing the tools on which these adhesives will be deposited. Engineering these structures will need to take into account how wastewater flows through a treatment plant: the tool’s structure will be determined by the turbulence of the water.
Co-principal investigator Jose Alfaro, whose work focuses on sustainability and development, and the circular economy, will perform sustainability analyses of repurposing the captured microplastic. Alfaro, an assistant professor of environmental practice in the School for Environment and Sustainability, will analyze the sustainability of this microplastic capture using a "triple bottom line” approach that evaluates the costs and benefits of new technologies in terms of profit, planet and people.
"Including sustainability considerations from the beginning of an emerging technology is a huge advantage,” he said. "The opportunities for impact are much greater at the design stage, allowing us to anticipate pitfalls. This is an area ripe for research opportunities that we hope to contribute.
"I am incredibly thankful that we get to work on this project with amazing faculty colleagues and students. I am also so thrilled that the whole team, but especially with the leadership of Anne McNeil, is committed to put DEI efforts at the heart of what we are doing.”
Finally, the grant also includes support to create what’s called a REU Program, or Research Experience for Undergraduates Program. McNeil’s focus is on neurodiverse individuals, particularly students on the autism spectrum. The aim is to provide these individuals with lab experiences in settings that are supportive of their needs.
"Almost nothing is known about how to support autistic students in the research environment,” she said. "I’ve gathered some information from reading about how to support autistic high school students in science discourse, and then we’ll draw on research about how to support autistic adults in the workplace. We’ll unite these to create research experiences for undergraduates.”