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Green nanotechnology

By William Meiners

Green nanotechnology

Author: William Meiners
Magazine Section: Innovate
College or School: CoE
Article Type: Issue Feature
Page CSS: #article-banner { background-position: center bottom !important;}
Feature Intro: From highways to high rises, construction in today's engineering world increasingly calls upon new environmentally friendly and inexpensive materials. One research collaboration is studying nature and nanotechnology to provide such materials.

From highways to high rises, new construction in today's engineering world increasingly calls upon materials to be sustainable, environmentally friendly and inexpensive. One Purdue Engineering research collaboration has looked to nature and nanotechnology to provide such materials. Their discovery: the use of cellulose nanocrystals (CNCs) can increase the flexural strength of concrete by 30 percent.

Working in the Pankow Materials Laboratory in a collaboration with the lab’s director, Jason Weiss, the Jack and Kay Hockema Professor of Civil Engineering, the research team consisted of Jeffrey Youngblood, associate professor of materials engineering; Pablo Zavattieri (PhD ’00), associate professor of civil engineering; Robert Moon (MSE ’96, PhD ’00), a researcher from the U.S. Forest Service’s Forest Products Laboratory; and Yizheng Cao (PhD ’14). Their findings were published in the February 2015 journal Cement and Concrete Composites.

A quintet’s quest

Five years ago, Moon, an internationally recognized expert in the subject matter, helped gather the unlikely collaborators on campus to discuss the potential different uses for CNCs, which can be refined from byproducts in the paper, bioenergy, agriculture and pulp industries. Youngblood brought a distinct chemistry and nanotechnology background to Weiss’ lab and its traditional strong suit in concrete. Zavattieri’s expertise resides in mechanics, as well as understanding nature’s role in novel advanced materials and nanotechnology.

“When collaborations are really effective, you can count on everybody to make sure their own discipline and knowledge base is covered,” Weiss says. The group pondered a lot of “what if” questions and used the collective efforts of everyone in the group to guide the research. “Where we really begin to make advancements is in the center of the table where you need everyone’s expertise to move the project forward.”

With funding from the National Science Foundation, the researchers addressed a particular challenge of today’s concrete — limits on strength and durability as a result of the pores and defects left after cement particles are hydrated and mixed. They discovered that CNCs added to the mix stuck to the surface of cement particles, increasing the hydration of the cement while using less water.

“All of the sudden, we’re getting stronger concrete,” Youngblood says.

As the CNCs are adsorbed onto the surface of the cement, they somehow change the way the cement is hydrated. The reasons for this still need to be explored, Youngblood says. But the result is a reduced “yield stress” of the slurry, making the cement more workable and of higher strength due to increased hydration, both of which are good for high-performance concrete.

Zavattieri describes the collaboration as a real eye-opener. It was his first chance to apply the concepts of changing the mechanical properties of concrete using nanomaterials. “Unlike other nanomaterials, CNCs do not directly reinforce the cement by bridging cracks,” he says. “But they are beneficial in their ability to attract water, which ultimately improves hydration.”

Abundant renewables

Zavattieri has long looked to nature to better understand the mechanics and biomimicry of naturally occurring, high-performance materials. These investigations often take him into the animal kingdom to explore biomineralized marine organisms including mollusk shells, radular teeth and crustacean exoskeletons. His team has also looked at ironclad bugs, trilobites, boxfish and fish scales. The concrete collaboration put his focus squarely on plant life. Extracted from structures called “cellulose microbils,” CNCs give plants and trees their strength, light weight and a resilience likened to the stiffness of steel.

The good news, Zavattieri says, is the abundance of this renewable material, which can be harvested from various low-quality cellulose feedstocks already being produced in different industrial processes.

It’s a green material that Weiss believes offers alternatives to other nanomaterials like carbon nanotubes. “If we continue to see improvements in strength or hydration like we’re seeing now, there’s a potential to ‘nano-modify’ what’s happening inside the system,” he says. “By doing this we have a product that’s both green and economically viable.”

In ramping up the scale to create bigger samples, Zavattieri says, there might be some initial expense in creating the biomass, but ultimately it will be cheaper.

Obtaining the materials requires little energy. “We can get CNCs from wood pulp, just like they make paper,” Youngblood says. “It can also be made from waste biomass. When you need more, you just grow more.”

Next steps

In scaling up the research and looking at options for commercialization, the engineers have a few more questions to answer within a forecasted three-year window. Youngblood says they’re still in the experimental phase because they need to understand exact reasons for the successful use of CNCs in concrete.

Weiss says, “We have to understand how variations in cement composition and variations in mixture proportions influence the performance of concrete, and the information we are currently gathering is vital to helping us scale up the process. We’ll also be looking at CNCs that come from different pilot plants that are coming online as they differ. Then we’ll have to get the civil engineering community accustomed to what they can expect from these materials.”

Cao, who earned his PhD in materials engineering while working with all four researchers, speaks to the benefits of his multidisciplinary education. As a graduate student on the project, he was responsible for designing research plans, conducting experiments, analyzing data and writing papers.

“I benefited a lot since my study was not limited to a specific area, and I learned to communicate with researchers in different methodologies,” he says. “This is very important, as in today’s world many problems need to be solved in a teamwork environment with multidisciplinary efforts. It was also challenging as my research had to convince four professors with different backgrounds and thought processes. This is more difficult than satisfying one advisor, as is the case for most PhD students.”

Cao hopes to land a job as either a research and development scientist in industry or as a professor at a research university. The Purdue engineers hope to get the technology on a commercial track. The P3Nano, a public-private partnership supporting development and use of wood-based nanomaterial for a wide range of commercial products, should further that cause.