Chemicals

Liangbin Hu makes wood stronger than steel

Credit: Provided by Liangbin Hu / University of Maryland

Lianbin Hu keeps pieces of super wood made by removing lignin from linden and compressing. Superwood is as strong as steel but light, making it ideal for construction use.

Ordinary old wood becomes a miraculous material in Liangbin Hu’s laboratory. Material from the University of Maryland, College Park, materials scientist and colleagues made the material transparentas strong as steel, shaky and bouncy like rubber, and more recently, molded like plastic.

Welcome

Hometown: Hubei Province, China

Current position: Professor of Mechanical Engineering, University of Maryland, College Park

Education: Bachelor, Physics, University of China Science and Technology, 2002; PhD, Physics, University of California, Los Angeles, 2007

Favorite species of wood that you can tinker with: Linden, a tree native to eastern North America

If you weren’t a materials engineer, you would be: School teacher

Using simple chemical processes, Hu’s laboratory partially leaches out lignin – a polymer that holds cellulosic fibers in wood together – and uses the natural complexity of wood nanostructures. Hu has licensed technology to InventWood, a branch company of the University of Maryland that seeks commercial applications such as cleaner materials that can replace glass, metal and plastic in buildings and vehicles.

Hu studied carbon nanotubes for his PhD thesis. He was drawn to wood when he found that the structure and ionic capabilities of cellulosic nanofibers were similar to those of carbon nanotubes, but they were stable and low cost.

Prachi Patel spoke with Hu about the properties of wood, which are often ignored, and about the use of biomaterials that his lab envisages in the future. This interview has been edited for length and clarity.

Why is wood a good material to develop?

If I had read a textbook on the structure of wood and chemistry, I would never have worked with this material because it is so complicated. I dared to work with him because I really liked the nanofibers.

The nanoscale of wood has mechanical properties very similar to carbon nanotubes made in the laboratory. A tree is an isotropic structure – it has a well-defined direction of growth. If you look at the wood under a microscope, you will see these tubular structures, these hollow fibers pointing in the same direction, glued together with lignin. And inside the cell wall of each fiber you see these amazing nanofibers that are four orders of magnitude smaller than large fibers. The typical strength of a piece of wood is about 20-50 MPa, but the nanofiber is about 100 times stronger. Thus, microscopic wood building blocks have a unique structure and amazing properties that we could take advantage of by removing lignin chemically.

Trees also efficiently pump ions and water 24/7. So we want to study the transport of ions in these tiny fibers and see if we can do it for batteries.

What applications for nanoengineered wood are we likely to see in the near future?

This is a question InventWood, which has licensed technology in my lab, asks almost every day. Structural use of modern wood – such as heavy-duty wood and the wood we have demonstrated – can occur in 2-3 years.

Utilizing our lab’s superwood, which truly takes advantage of the mechanical properties of nanofibers and has a material strength similar to some metals, we are looking to replace steel and aluminum to save carbon emissions. The production of these metals uses a lot of heat and electricity and emits a lot of carbon dioxide. But growing wood removes carbon dioxide, and our method of treating wood at room temperature using water, sodium sulfite and sodium hydroxide is more energy efficient.

And now for the first time we can mold wood the way you can mold plastic and metal. If you think of plastics, you can melt them and change shape, but if you try to bend wood, you can break it. Our material is environmentally friendly compared to plastic composites because this material is, after all, biodegradable but still retains strength for structural applications.

On the other hand, the battery has many components; everything has to work together and you have to compete with many other technologies. So I think the use of wood to make batteries will require more development.

Why are you interested in the ionic properties of wood for batteries?

Wood is used mainly as a construction material or for making paper. But his interesting physics and chemistry go on a nanoscale. For example, in tiny nanofibers ions move much faster than in large fibers because in tiny space ions can only go one at a time and have to get rid of all their counterions that normally attract them and hold them back. This speed is very important for the battery where you move lithium ions while charging. One of the reasons your battery doesn’t charge fast enough is that lithium ions come along with copper ions and aren’t very mobile. With such a nanofiber structure you could adapt as ions move.

In general, people have tried to create new nanomaterials. But wood nanofibers are the most common material around us, averaging about 400 trees per person. We really need to study wood nanotechnology more.

What are the limitations when creating new wood materials? How could you overcome them?

Everything has a downside. We do not add anything to the forest. That is why it is stable and biodegradable. But in the end, it’s a piece of wood. If you put it on the fire long enough, it will catch fire. But the wood-based materials we make ignite much more slowly, at one hundredth the speed of natural wood.

Wood also has size limitations, and the shape is not always straight. So we have to be smart in how to deal with that. For example, we try to bypass the size of the wood by cutting it into a rotor. The diameter of the wood is limited, but if you can clean it in a spiral and roll it out, you can make a piece much bigger.

What do you do with the lignin you get from wood?

The paper industry has a saying that is possible make anything out of lignin other than money. There has never been a good way to use lignin. We’re trying to turn that around and do something that can benefit lignin, instead of trying to remove it. We have not yet fully focused on the development or processing of lignin, but we have something very interesting going on here, which I hope to talk to you about in the future.

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Patel Patel is a freelance journalist from Pittsburgh who writes about energy, materials science, nanotechnology, biotechnology and computers. A version of this story first appeared in ACS Central Science: cenm.ag/superwood.

https://cen.acs.org/materials/nanomaterials/Liangbing-Hu-makes-wood-stronger-than-steel/100/i7?utm_source=LatestNews&utm_medium=LatestNews&utm_campaign=CENRSS Liangbin Hu makes wood stronger than steel

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