WITH AMERICANS CONSUMING MORE THAN 100 BILLION POUNDS EVERY YEAR, the U.S. appetite for plastic is virtually
inexhaustible. Of that, approximately 30 billion
pounds is polyethylene, the kind of plastic used in everything from product packaging and shrink-wrap to re-sealable sandwich bags.
Polyethylene is produced from petroleum in an energy-intensive manufacturing process that releases
large amounts of carbon dioxide into the atmosphere.
How much exactly is 30 billion pounds?
“I did a calculation once that shows you can fill the Minneapolis Metrodome about 10 times with that amount of polyethylene,” said Marc Hillmyer, University
of Minnesota professor of chemistry. And all of it, he points out, is essentially non-biodegradable.
Chemistry professor, Marc Hillmyer, is developing polymers or plastics that mimic petroleum-based materials but are made from renewable resources that can be composted and are carbon neutral. These new environment-friendly plastics will contribute substantially less greenhouse gas into the atmosphere.
Hillmyer, who oversees a 25-member research team, is working to change that equation. His objective
is to develop polymers—or plastics—that mimic the properties of petroleum-derived materials but are made from renewable resources that can be composted
and are carbon neutral, contributing substantially
less greenhouse gas into the atmosphere.
The renewable sources for these “natural” polymers
can be grouped into a few broad categories: carbohydrates, like sugar and starches; vegetables oils, like soy, canola, and sunflower; and turpine, like menthol, the volatile oil found in plants of the mint family, and limonene, which comes from the peel of citrus fruits.
“I am trying to understand the chemistry of these compounds and how to convert them into new polymeric
materials that can be competitive with more traditional petroleum-based plastics,” he explains. The challenges are both economic and scientific. When oil is cheap, it’s hard to come up with a competitively
priced renewable plastic. When oil is expensive—
as it is today—renewable plastics begin to look more attractive.
As for the scientific challenges: “The focus of my work is on how to change these [renewable resources]
into useful precursors for polymers,” he explains. “The natural materials are often not useful right from the plant. We have to figure out how to manipulate them into forms that are usable.
The molecular model shown above is a poly-mer precursor derived from menthol, which is a readily available natural resource.
Some of this work draws upon his background in organic chemistry, but Hillmyer also collaborates with inorganic chemists to develop catalysts that can convert natural materials into polymers with properties more like conventional polyethylene. For example, a project he undertook that was sponsored by Cargill involved collaborative work with Bill Tolman,
another University of Minnesota chemistry professor who specializes in inorganic chemistry, in research on 3-hydroxy propionic acid, a molecule derived
from sugar.
“We were interested in looking at how to convert that molecule into a polymer and came up with a novel way to change it into a high molecular weight material,” he explains. It was so successful, he and Tolman ended up patenting the process. Meanwhile, as the price—both in dollars and in environmental damage—of petroleum-based plastics continues to rise, other companies have begun to search for renewable
replacements. The Toyota Corporation is currently funding another project by Hillmyer’s research
team into bio-renewable polymers that may be used in the company’s automobiles. Hillmyer also foresees applications for renewable plastics in biomedical
products like stents, sutures and drug delivery
vehicles that could degrade naturally and harmlessly
inside the body once their work is completed.
“It’s an exciting field to be in today,” he said. “What I like most is the challenge. It’s not easy turning
something like menthol into a useful plastic. But it can be done. In the long-run, the success of renewable
polymers is just a matter of time.””
