Ultra-strong nanocrystals from biomass make plastic 3,000 times stronger - integrating biofuel production and nanotech
This vision of an integrated and sustainable 'bioeconomy' is becoming ever more realistic because different scientific fields are merging and overlapping. Researchers at the State University of New York (SUNY) College of Environmental Science and Forestry (ESF), for example, are developing ways to use cellulose from wood to strengthen plastics, providing a lightweight component that has the added advantage of being biodegradable. Their future aim: to integrate the process with the production of next-generation ethanol.
The researchers succeeded in pulling ultra-strong cellulose nanocrystals (CNXLs) out of biomass from trees and willow shrubs to orange pulp and the pomace left behind after apple cider production, and mixing them with plastics. “By adding an ounce of crystals to a pound of plastic, you can increase the strength of the plastic by a factor of 3,000,” said Dr. William T. Winter, a chemistry professor and director of the Cellulose Research Institute at ESF. “And in the end, in a landfill, it’s just carbon dioxide and water, which can be taken up and made into more biomass.”
“All plant materials contain a minimum of 25 percent cellulose,” Winter says. “Wood from trees is a little higher, between 40 percent and 50 percent.” In addition to being used as strengtheners in plastics, the nanocrystals can be used in ceramics and in biomedical applications such as artificial joints and disposable medical equipment (for a more in-depth introduction on CNXLs and their possible applications, see "The Material Science of Nanocrystals" [*pdf], and Dr. John Simonsen's Cellulose Nanocrystal Composites website.) Using cellulosic nanocrystals to strengthen plastics has advantages over the glass that is often used: glass is heavier, harder on processing machinery and therefore more expensive to work with, and it stays in the ground for centuries. The cellulose nanocrystals will break down quickly in a landfill:
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“Anything which is made in nature can be destroyed in nature,” Winter said. “And these cellulose particles have a lifetime in a landfill of less than 90 days, at which time, they go back into carbon dioxide and water. It can be reabsorbed by other plants that use it to make more cellulose.”
Winter and his team work with a reactor that can process up to 500 grams (about a pound) of material at a time, a significant increase over the 5-gram quantities that are typically used in laboratory settings. The next step is to scale it up to a commercial level.
In Winter’s process, the cellulose is first purified in the laboratory as substances such as wax and gluey lignin are removed from the biomass. The cellulose then goes through a homogenizing process, similar to the one used with dairy products. The cellulose is shredded into tiny particles under high pressure, rendering nanocrystals, so-called because they are so miniscule they are measured in nanometers, or billionths of a meter.
The result is a viscous, white liquid that goes into a microcompounder, where it is mixed with plastic under high pressure. The unit produces a cord – or a ribbon, depending on the die being used to shape it – of crystal-reinforced plastic that can tested for several properties.
Winter’s team is currently working on refining the surface of the crystals so they adhere better to the plastic, and disbursing the crystals throughout the material to achieve the best results.
Integrating with ethanol production
In the future, Winter said, the process could be tied to the production of cellulosic ethanol. When hemicellulose is removed from wood for fermentation into ethanol, it leaves behind cellulose that can be treated with enzymes and reduced to the nanocrystals Winter uses in his lab. The value of those crystals in industrial uses represents a significant reduction in the cost of producing ethanol.
And Winter sees possibilities in using the nanocrystals in the bioplastics that are being developed at SUNY-ESF, resulting in strong, lightweight plastics that would degrade in a landfill.
Winter has received more than $1 million in support for the research, mostly from federal sources such as the departments of agriculture and energy, and the Environmental Protection Agency. Other funding has come from Eastman Chemical Company.