Page 66 - Plastics News July 2019

teChNoLogy

Polymers to convert thermal energy to electricity

team at the University of Massachusetts Amherst led by into polymers to improve their ability to move electric
A chemist Dhandapani Venkataraman, "DV," and electrical charges and boost efficiency. DV says, "Imagine that
engineer Zlatan Aksamija, report this month in Nature we've added chocolate chips, a material that improves
Communications on an advance they outline toward conductivity, to a cookie. That's doping."But doping
more efficient, cheaper, polymer-based harvest of heat involves a tradeoff, Aksamija adds. It can either achieve
energy. By one official estimate, American manufacturing, more current and less thermally-induced voltage, or more
transportation, residential and commercial consumers voltage and less current, but not both. "If you improve one
use only about 40 percent of the energy they draw on, property, you make the other worse," he explains, "and
wasting 60 percent. Often, this wasted energy escapes as it can take a lot of effort to decide the best balance," or
heat, or thermal energy, from inefficient technology that optimal doping.
fails to harvest that potential power. "It will be a surprise To address this, DV and his chemistry Ph.D. student Connor
to the field," DV predicts, "it gives us another key variable Boyle, with Aksamija and his electrical engineering Ph.D.
we can alter to improve the thermo-electric efficiency student Meenakshi Upadhyaya worked in what DV calls "a
of polymers. This should make us, and others, look at
true collaboration," where each insight from numerical

polymer thermo-electrics in a new light." Aksamija explains, simulations informed the next series of experiments, and
"Using polymers to convert thermal energy to electricity vice versa.The chemists conducted experiments, while the
by harvesting waste heat has seen an uptick in interest engineering team performed efficiency analyses along the
in recent years. Waste heat represents both a problem but curve from "zero doping" to "maximum doping" to identify
also a resource; the more heat your process wastes, the the best balance for many different materials. For the
less efficient it is." Harvesting waste heat is less difficult massive number of simulations they ran to test hundreds
when there is a local, high-temperature gradient source of scenarios, they used the Massachusetts Green High
to work with, he adds, such as a high-grade heat source like Performance Computing Center in nearby Holyoke.
a power plant.Thermo-electric polymers are less efficient
at heat harvesting compared to rigid, expensive-to- Aksamija says. "We can now tell you, for every given
produce inorganic methods that are nevertheless quite material, what is the optimal balance of the two
efficient, Aksamija adds, but polymers are worth pursuing properties, and for a while, people were satisfied
because they are cheaper to produce and can be coated with just knowing that." But along the way, he adds,
on flexible materials -- to wrap around a power plant's they discovered an entirely new variable that had not
exhaust stack, for example.Recently, scientists have been yet been accounted for, one that turned out to be critical
addressing this obstacle with a process called "doping." to the doped polymer's ability to harvest thermal energy
With it, researchers mix chemical or other components efficiently. He says, "The original analysis didn't get

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