Sturdy Insulator Made of Wood

Authored by aero.umd.edu and submitted by mvea

Sturdy Insulator Made of Wood COLLEGE PARK-- Engineers at the University of Maryland have created a new material that’s as insulating as Styrofoam, but stronger and much more environmentally friendly. “This can insulate better than most other current thermal insulators, including Styrofoam. It is extremely promising to be used as energy efficient building materials,” said Tian Li, a postdoc student with Liangbing Hu’s group in the UMD department of materials science and engineering. She was named to Forbes Magazine’s “30 under 30” list of accomplished young adults in 2018. Wood “conducts” heat along the channels that were used when the tree was alive to shuttle water and nutrients from roots to leaves. However, heat trying to cross the wood grain is blocked. With the wood oriented in the right direction, heat could be blocked or transmitted as the designer desires. To test how much heat was insulated, they measured the temperature on one side of the nanowood, while on the other side of the wood, shining a light in one test and applying heat in another test. The nanowood insulated better in both cases. The wood blocked at least 10 degrees more heat than styrofoam or silica aerogel, which had been awarded the Guinness World Record for ‘best insulator’. The nanowood, which is white, also effectively reflects sunlight. They also tried to crush it and found that, in one direction, the nanowood was 30 times stronger than commercially used thermal insulation materials such as Styrofoam, aerogel or other foams made of cellulose. Nanowood’s tiny fibers don’t cause allergic reactions or irritate lung tissues, unlike glass or wool insulators. The secret to the nanowood is the removal of lignin, the part that makes it brown and rigid. The team also removed some of the short fibers that tangle themselves in with the cellulose fibers that make up the scaffolding-like base structure of the wood. The aligned cellulose fibers then bond with each other and results in a high mechanical strength. The team in the US was assisted by Lars Wågberg of the KTH Royal Institute of Technology, in Stockholm, Sweden. This member of the Wallenberg Wood Science Centre helped analyze the behavior of cellulose fibers in the nanowood. “My research program experiments with nature’s nanotechnology that we see in wood,” said Liangbing Hu, an associate professor in the department of materials science and engineering at the University of Maryland, a member of the Maryland Energy Innovation Institute, and a member of the Maryland NanoCenter. “We are reinventing ways to use wood that could be useful in constructing energy efficient and environmentally friendly homes.” These wood-based nanotechnologies are being commercialized through Inventwood, a UMD spinoff company of Hu’s research group. The team has made the insulating nanowood in blocks and in a thin, flexible or rollable, form. Photos of the wood's microstructures were produced in the Advanced Imaging and Microscopy (AIM) Lab, part of the Maryland NanoCenter, which is headquartered in College Park. The research was published in the journal Science Advances on March 9. ‘Anisotropic, lightweight, strong, and super thermally insulating nanowood with naturally aligned nanocellulose’ Li et al, Science Advances, 2018 http://dx.doi.org/

tuctrohs on March 10th, 2018 at 13:58 UTC »

A little hype mitigation:

1) The anisotropic conductivity is useful for something like a heat shield--protecting nearby materials or electronics from a flame or heating element, for example. But for such applications, high-temperature capability is typically needed. It doesn't seem likely that this material would survive high temperature well at all. Also, it's easy to create a composite material with much better lateral thermal conductivity by stacking layers of aluminum and insulation.

2) The usefulness in building applications is likely limited by production cost and, as someone else mentioned, flammability. The claim of "much more environmentally friendly" would require investigation of things like the energy use in the freeze-drying process and consideration of how the chemicals used in removing the lignin are managed.

3) The combination of low thermal conductivity and moderately high strength could be useful in many building applications, if the other issues are addressed. I'm disappointed that the authors didn't compare it to materials that target that combination such as Compacfoam and Foamglas. It does appear that they have achieved a better combination of those two properties than the commercially available materials. Both the commercial materials are completely waterproof, which is not the case for this material. In some applications that doesn't matter, and in some others, the moisture permeability of the new material is actually an advantage.

4) The low emissivity is interesting but is not likely to be of much practical value. It's only in the solar spectrum range, not in the thermal radiation range where it would be of value for insulation. To be useful in reflecting unwanted solar radiation, it would need to be exposed to the sun, but it's not likely to hold up to rain or UV radiation if it was used exposed on a roof, for example. Also, white paint can accomplish a similar function, and there are white paints that work pretty well outdoors.

LazyWolverine on March 10th, 2018 at 13:16 UTC »

what are the fire retardant properties of this material compared to glass insulating which are very resistant to fire.

mvea on March 10th, 2018 at 11:17 UTC »

The title of the post is a cut and paste from the following sections of the linked academic press release here:

Engineers at the University of Maryland have created a new material that’s as insulating as Styrofoam, but stronger and much more environmentally friendly.

And here:

They also tried to crush it and found that, in one direction, the nanowood was 30 times stronger than commercially used thermal insulation materials such as Styrofoam, aerogel or other foams made of cellulose.

Nanowood’s tiny fibers don’t cause allergic reactions or irritate lung tissues, unlike glass or wool insulators.

The secret to the nanowood is the removal of lignin, the part that makes it brown and rigid. The team also removed some of the short fibers that tangle themselves in with the cellulose fibers that make up the scaffolding-like base structure of the wood. The aligned cellulose fibers then bond with each other and results in a high mechanical strength.

For those interested, here is a link to a popular press article on the same study:

https://www.inverse.com/article/42101-energy-saving-nanowood-will-build-homes

From this article, I got the reference to the colour of the material changing here:

“When you remove this yellowish-component [lignin], the wood is still a piece of wood but it becomes completely white,” Liangbing Hu, an assistant professor at the University of Maryland, tells Inverse. “It also becomes much lighter because we’re removing material from the wood and it becomes an excellent insulator. So you can use it for the walls of your home to save energy on air-conditioning and heating.”

Journal reference:

Anisotropic, lightweight, strong, and super thermally insulating nanowood with naturally aligned nanocellulose

Tian Li1,, Jianwei Song1,, Xinpeng Zhao2,, Zhi Yang3,, Glenn Pastel1, Shaomao Xu1, Chao Jia1, Jiaqi Dai1, Chaoji Chen1, Amy Gong1, Feng Jiang1, Yonggang Yao1, Tianzhu Fan2, Bao Yang3, Lars Wågberg4,5, Ronggui Yang2,† and Liangbing Hu1,†

Science Advances 09 Mar 2018: Vol. 4, no. 3, eaar3724

DOI: 10.1126/sciadv.aar3724

Link: http://advances.sciencemag.org/content/4/3/eaar3724.full

Abstract

There has been a growing interest in thermal management materials due to the prevailing energy challenges and unfulfilled needs for thermal insulation applications. We demonstrate the exceptional thermal management capabilities of a large-scale, hierarchal alignment of cellulose nanofibrils directly fabricated from wood, hereafter referred to as nanowood. Nanowood exhibits anisotropic thermal properties with an extremely low thermal conductivity of 0.03 W/m·K in the transverse direction (perpendicular to the nanofibrils) and approximately two times higher thermal conductivity of 0.06 W/m·K in the axial direction due to the hierarchically aligned nanofibrils within the highly porous backbone. The anisotropy of the thermal conductivity enables efficient thermal dissipation along the axial direction, thereby preventing local overheating on the illuminated side while yielding improved thermal insulation along the backside that cannot be obtained with isotropic thermal insulators. The nanowood also shows a low emissivity of <5% over the solar spectrum with the ability to effectively reflect solar thermal energy. Moreover, the nanowood is lightweight yet strong, owing to the effective bonding between the aligned cellulose nanofibrils with a high compressive strength of 13 MPa in the axial direction and 20 MPa in the transverse direction at 75% strain, which exceeds other thermal insulation materials, such as silica and polymer aerogels, Styrofoam, and wool. The excellent thermal management, abundance, biodegradability, high mechanical strength, low mass density, and manufacturing scalability of the nanowood make this material highly attractive for practical thermal insulation applications.