Tag Archives: Teng Li

Wood’s natural nanotechnology

“Wood’s natural nanotechnology: is an unusual term and it comes at the end of this February 7, 2018 University of Maryland (US) news release about a technique which will make wood stronger than titanium alloy,

Engineers at the University of Maryland in College Park have found a way to make wood more than ten times times stronger and tougher than before, creating a natural substance that is stronger than titanium alloy.

“This new way to treat wood makes it twelve times stronger than natural wood and ten times tougher,” said Liangbing Hu, the leader of the team that did the research, to be published on Thursday [February 7, 2018] in the journal Nature. “This could be a competitor to steel or even titanium alloys, it is so strong and durable. It’s also comparable to carbon fiber, but much less expensive.” Hu is an associate professor of materials science and engineering and a member of the Maryland Energy Innovation Institute.

“It is both strong and tough, which is a combination not usually found in nature,” said Teng Li, the co-leader of the team and the Samuel P. Langley associate professor of mechanical engineering at the University of Maryland. His team measured the dense wood’s mechanical properties.  “It is as strong as steel, but six times lighter. It takes 10 times more energy to fracture than natural wood. It can even be bent and molded at the beginning of the process.”

The team’s process begins by removing the wood’s lignin, the part of the wood that makes it both rigid and brown in color. Then it is compressed under mild heat, at about 150 F. This causes the cellulose fibers to become very tightly packed. Any defects like holes or knots are crushed together.  The treatment process was extended a little further with a coat of paint.

The scientists found that the wood’s fibers are pressed together so tightly that they can form strong hydrogen bonds, like a crowd of people who can’t budge – who are also holding hands. The compression makes the wood five times thinner than its original size.

The team also tested the material by shooting a bullet-like projectile at it. Unlike natural wood, which was blown straight through, the fully treated wood actually stopped the projectile partway through.

“Soft woods like pine or balsa, which grow fast and are more environmentally friendly, could replace slower-growing but denser woods like teak, in furniture or buildings,” Hu said.

“The paper provides a highly promising route to the design of light weight high performance structural materials, with tremendous potential for a broad range of applications where high strength, large toughness and superior ballistic resistance are desired, “ said Dr. Huajian Gao, a professor at Brown University, who was not involved in the study. “It is particularly exciting to note that the method is versatile for various species of wood and fairly easy to implement.”

“This kind of wood could be used in cars, airplanes, buildings – any application where steel is used,” Hu said.

“The two-step process reported in this paper achieves exceptionally high strength, much beyond what [is] reported in the literature,” said Dr. Zhigang Suo, a professor of mechanics and materials at Harvard University, also not involved with the study. “Given the abundance of wood, as well as other cellulose-rich plants, this paper inspires imagination.”

“The most outstanding observation, in my view, is the existence of a limiting concentration of lignin, the glue between wood cells, to maximize the mechanical performance of the densified wood. Too little or too much removal lower the strength compared to a maximum value achieved at intermediate or partial lignin removal. This reveals the subtle balance between hydrogen bonding and the adhesion imparted by such polyphenolic compound. Moreover, of outstanding interest, is the fact that that wood densification leads to both, increased strength and toughness, two properties that usually offset each other,” said Orlando J. Rojas, a professor at Aalto University in Finland.

Hu’s research has explored the capacities of wood’s natural nanotechnology [emphasis mine]. They previously made a range of emerging technologies out of nanocellulose related materials: (1) super clear paper for replacing plastic; (2) photonic paper for improving solar cell efficiency by 30%; (3) a battery and a supercapacitor out of wood; (4) a battery from a leaf; (5) transparent wood for energy efficient buildings; (6) solar water desalination for drinking and specifically filtering out toxic dyes. These wood-based emerging technologies are being commercialized through a UMD spinoff company, Inventwood LLC.

At a guess, “wood’s natural nanotechnology” refers to the properties of wood and other forms of cellulose at the nanoscale.

Here’s a link to and a citation for the paper,

Processing bulk natural wood into a high-performance structural material by Jianwei Song, Chaoji Chen, Shuze Zhu, Mingwei Zhu, Jiaqi Dai, Upamanyu Ray, Yiju Li, Yudi Kuang, Yongfeng Li, Nelson Quispe, Yonggang Yao, Amy Gong, Ulrich H. Leiste, Hugh A. Bruck, J. Y. Zhu, Azhar Vellore, Heng Li, Marilyn L. Minus, Zheng Jia, Ashlie Martini, Teng Li, & Liangbing Hu. Nature volume 554, pages 224–228 (08 February 2018) doi:10.1038/nature25476 Published online: 07 February 2018

This paper is behind a paywall.

h/t Feb. 7, 2018 news item on Nanowerk and, finally, you can find out more about the wood-based emerging technologies being commcercialized by the University of Maryland here on the Inventwood website.

Replacing metal with nanocellulose paper

The quest to find uses for nanocellulose materials has taken a step forward with some work coming from the University of Maryland (US). From a July 24, 2015 news item on Nanowerk,

Researchers at the University of Maryland recently discovered that paper made of cellulose fibers is tougher and stronger the smaller the fibers get … . For a long time, engineers have sought a material that is both strong (resistant to non-recoverable deformation) and tough (tolerant of damage).

“Strength and toughness are often exclusive to each other,” said Teng Li, associate professor of mechanical engineering at UMD. “For example, a stronger material tends to be brittle, like cast iron or diamond.”

A July 23, 2015 University of Maryland news release, which originated the news item, provides details about the thinking which buttresses this research along with some details about the research itself,

The UMD team pursued the development of a strong and tough material by exploring the mechanical properties of cellulose, the most abundant renewable bio-resource on Earth. Researchers made papers with several sizes of cellulose fibers – all too small for the eye to see – ranging in size from about 30 micrometers to 10 nanometers. The paper made of 10-nanometer-thick fibers was 40 times tougher and 130 times stronger than regular notebook paper, which is made of cellulose fibers a thousand times larger.

“These findings could lead to a new class of high performance engineering materials that are both strong and tough, a Holy Grail in materials design,” said Li.

High performance yet lightweight cellulose-based materials might one day replace conventional structural materials (i.e. metals) in applications where weight is important. This could lead, for example, to more energy efficient and “green” vehicles. In addition, team members say, transparent cellulose nanopaper may become feasible as a functional substrate in flexible electronics, resulting in paper electronics, printable solar cells and flexible displays that could radically change many aspects of daily life.

Cellulose fibers can easily form many hydrogen bonds. Once broken, the hydrogen bonds can reform on their own—giving the material a ‘self-healing’ quality. The UMD discovered that the smaller the cellulose fibers, the more hydrogen bonds per square area. This means paper made of very small fibers can both hold together better and re-form more quickly, which is the key for cellulose nanopaper to be both strong and tough.

“It is helpful to know why cellulose nanopaper is both strong and tough, especially when the underlying reason is also applicable to many other materials,” said Liangbing Hu, assistant professor of materials science at UMD.

To confirm, the researchers tried a similar experiment using carbon nanotubes that were similar in size to the cellulose fibers. The carbon nanotubes had much weaker bonds holding them together, so under tension they did not hold together as well. Paper made of carbon nanotubes is weak, though individually nanotubes are arguably the strongest material ever made.

One possible future direction for the research is the improvement of the mechanical performance of carbon nanotube paper.

“Paper made of a network of carbon nanotubes is much weaker than expected,” said Li. “Indeed, it has been a grand challenge to translate the superb properties of carbon nanotubes at nanoscale to macroscale. Our research findings shed light on a viable approach to addressing this challenge and achieving carbon nanotube paper that is both strong and tough.”

Here’s a link to and a citation for the paper,

Anomalous scaling law of strength and toughness of cellulose nanopaper by Hongli Zhu, Shuze Zhu, Zheng Jia, Sepideh Parvinian, Yuanyuan Li, Oeyvind Vaaland, Liangbing Hu, and Teng Li. PNAS (Proceedings of the National Academy of Sciences) July 21, 2015 vol. 112 no. 29 doi: 10.1073/pnas.1502870112

This paper is behind a paywall.

There is a lot of research on applications for nanocellulose, everywhere it seems, except Canada, which at one time was a leader in the business of producing cellulose nanocrystals (CNC).

Here’s a sampling of some of my most recent posts on nanocellulose,

Nanocellulose as a biosensor (July 28, 2015)

Microscopy, Paper and Fibre Research Institute (Norway), and nanocellulose (July 8, 2015)

Nanocellulose markets report released (June 5, 2015; US market research)

New US platform for nanocellulose and occupational health and safety research (June 1, 2015; Note: As you find new applications, you need to concern yourself with occupational health and safety.)

‘Green’, flexible electronics with nanocellulose materials (May 26, 2015; research from China)

Treating municipal wastewater and dirty industry byproducts with nanocellulose-based filters (Dec. 23, 2014; research from Sweden)

Nanocellulose and an intensity of structural colour (June 16, 2014; research about replacing toxic pigments with structural colour from the UK)

I ask again, where are the Canadians? If anybody has an answer, please let me know.

Wooden batteries in Maryland (US)

There seems to be a gusher of interest in making wooden batteries. Last year, there was news from a joint Polish-Swedish research team (my Aug. 14, 2012 posting) who’d combined lignin with a conductive polymer (polypyrrole) to create a battery cathode. Today, June 19, 2013, Nanowerk featured a news item about a team at the University of Maryland (US) who are also using wood to make battery components (Note: A link has been removed),

A sliver of wood coated with tin could make a tiny, long-lasting, efficient and environmentally friendly battery (“Tin Anode for Sodium-Ion Batteries Using Natural Wood Fiber as a Mechanical Buffer and Electrolyte Reservoir”).

But don’t try it at home yet– the components in the battery tested by scientists at the University of Maryland are a thousand times thinner than a piece of paper. Using sodium instead of lithium, as many rechargeable batteries do, makes the battery environmentally benign. Sodium doesn’t store energy as efficiently as lithium, so you won’t see this battery in your cell phone — instead, its low cost and common materials would make it ideal to store huge amounts of energy at once – such as solar energy at a power plant.

The June 19, 2013 University of Maryland news release, which originated the news item, explains why this work with wood is so exciting (Note: Links have been removed),

Existing batteries are often created on stiff bases, which are too brittle to withstand the swelling and shrinking that happens as electrons are stored in and used up from the battery. Liangbing Hu, Teng Li and their team found that wood fibers are supple enough to let their sodium-ion battery last more than 400 charging cycles, which puts it among the longest lasting nanobatteries.

“The inspiration behind the idea comes from the trees,” said Hu, an assistant professor of materials science. “Wood fibers that make up a tree once held mineral-rich water, and so are ideal for storing liquid electrolytes, making them not only the base but an active part of the battery.”

Lead author Hongli Zhu and other team members noticed that after charging and discharging the battery hundreds of times, the wood ended up wrinkled but intact. Computer models showed that that the wrinkles effectively relax the stress in the battery during charging and recharging, so that the battery can survive many cycles.

Here’s a link to and a citation for the research paper,

Tin Anode for Sodium-Ion Batteries Using Natural Wood Fiber as a Mechanical Buffer and Electrolyte Reservoir by Hongli Zhu, Zheng Jia, Yuchen Chen, Nicholas Weadock, Jiayu Wan, Oeyvind Vaaland, Xiaogang Han, Teng Li, and Liangbing Hu. Nano Lett., Article ASAP DOI: 10.1021/nl400998t Publication Date (Web): May 29, 2013

Copyright © 2013 American Chemical Society

This paper is behind a paywall.