Tag Archives: cellulose nanofibres (CNF)

Plant fibers (nanocellulose) for more sustainable devices

Thank you to Junichiro Shiomi and the University of Tokyo for this image,

Caption: An artist’s interpretation of the way natural cellulose fibers are combined to form the CNF [cellulose nanofiber] yarn, and a magnified section showing the nanoscopic rod-shaped filaments within the yarn bundle. Credit: ©2022 Junichiro Shiomi

The research into cellulose nanofibers (CNFs) announced in this November 4, 2022 news item on ScienceDaily comes from the University of Tokyo,

Plant-derived materials such as cellulose often exhibit thermally insulating properties. A new material made from nanoscale cellulose fibers shows the reverse, high thermal conductivity. This makes it useful in areas previously dominated by synthetic polymer materials. Materials based on cellulose have environmental benefits over polymers, so research on this could lead to greener technological applications where thermal conductivity is needed.

Both cellulose nanofibers/nanofibres and cellulose nanofibrils are abbreviated to CNFs. This seems a bit confusing so I went looking for an explanation and found this September 22, 2020 posting (scroll down about 35% of the way) by professor Hatsuo Ishida, Department of Macromolecular Science and Engineering at Case Western Reserve University,

Both fiber and fibril indicate long thread-like materials and their meanings are essentially the same. However, the word,”fibril,” emphasizes a thin fiber. Therefore, the use of the word, “nano fibril,” is rather redundant. The word,”fibril” is often used for distinguishing high temperature water vapor treated cellulose fibers that are spread into very thin fibers from the whiskers prepared by the acid treatment of cellulosic materials. The word,” microfibril” is more often used than “nano fibril.” Some also use the word,”cellulose nanocrystal.” Cellulose whiskers are single crystals of materials and a typical length is less than a micrometer (one of the longest cellulose whiskers can be prepared from a sea creature called tunicate), whereas the cellulose nano fibril has much longer length. This material is much easier to scale up whereas cellulose whiskers are not as easily scale up as the nano fibrils. The word fiber has no implication and it is simply a thread like object. Thus, even if the diameter is more than hundred micrometers, as long as the length is much longer (high aspect ratio), you may call it a fiber, whereas such a thick fiber is seldom called a fibril.

Thank you professor Ishida!

A November 4, 2022 University of Tokyo press release (also on EurekAlert), which originated the news item, explains the interest in nanocellulose and its thermal properties,

Cellulose is a key structural component of plant cell walls and is the reason why trees can grow to such heights. But the secret of its material strength actually lies in its overlapping nanoscopic fibers. In recent years, many commercial products have used cellulose nanofiber (CNF) materials because their strength and durability make them a good replacement for polymer-based materials such as plastics that can be detrimental to the environment. But now and for the first time, a research team led by Professor Junichiro Shiomi from the University of Tokyo’s Graduate School of Engineering has investigated previously unknown thermal properties of CNF, and their findings show these materials could be even more useful still.

“If you see plant-derived materials such as cellulose or woody biomass used in applications, it’s typically mechanical or thermally insulating properties that are being employed,” said Shiomi. “When we explored the thermal properties of a yarn made from CNF, however, we found that they show a different kind of thermal behavior, thermal conduction, and it’s very significant, around 100 times higher than that of typical woody biomass or cellulose paper.”

The reason yarn made from CNF can conduct heat so well is due to the way it’s made. Cellulose fibers in nature are very disorganized, but a process called the flow-focusing method combines cellulose fibers, orientating them in the same way, to create CNF. It’s this tightly bound and aligned bundle of rod-shaped fibers that allows heat to transfer along the bundle, whereas in a more chaotic structure it would dissipate heat more readily.

“Our main challenge was how to measure the thermal conductivity of such small physical samples and with great accuracy,” said Shiomi. “For this, we turned to a technique called T-type thermal conductivity measurement. It allowed us to measure the thermal conductivity of the rod-shaped CNF yarn samples which are only micrometers (a micrometer equaling one-thousandth of a millimeter) in diameter. But the next step for us is to perform accurate thermal tests on two-dimensional textilelike samples.”

Shiomi and his team hope that their investigation and future explorations into the use of CNF as a thermally conductive material could give engineers an alternative to some environmentally damaging polymers. In applications where heat transfer is important, such as certain electronic or computational components, it could greatly reduce the consequences of discarded electronic equipment, or e-waste, thanks to the biodegradable nature of CNF and other plant-based materials.

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

Enhanced High Thermal Conductivity Cellulose Filaments via Hydrodynamic Focusing by Guantong Wang, Masaki Kudo, Kazuho Daicho, Sivasankaran Harish, Bin Xu, Cheng Shao, Yaerim Lee, Yuxuan Liao, Naoto Matsushima, Takashi Kodama, Fredrik Lundell, L. Daniel Söderberg, Tsuguyuki Saito, and Junichiro Shiomi. Nano Lett. 2022, 22, 21, 8406–8412 DOI: https://doi.org/10.1021/acs.nanolett.2c02057 Publication Date:October 25, 2022 Copyright © 2022 The Authors. Published by American Chemical Society

This paper is open access.

Cellulose nanofibers as an alternative material for petroleum-based plastics?

According to an October 25, 2022 news item on phys.org, scientists at Osaka University (Japan) may have found a new material to replace petroleum-based plastic materials,

Single-use plastics have saved many lives by improving sanitation in health care. However, the sheer quantity of plastic waste—which can take from tens to hundreds of years to decompose—is a global pollution scourge. But now, in a study recently published in ACS Nano, researchers from The Institute of Scientific and Industrial Research (SANKEN) at Osaka University and collaborating partners have developed exceptionally versatile hydrogels and moldings that might replace conventional plastics.

An October 27, 2022 Osaka University press release (also on EurekAlert but published October 21, 2022), which originated the news item, tells the story behind the research,

The global scale of plastic waste urgently requires solutions and is being addressed from diverse perspectives. For example, in August 2022, National Geographic published a feature on recycling and repurposing plastic waste. Nevertheless, “the only long-term solution is to develop inexpensive, high-performance, plastic-like alternatives that don’t persist in the environment,” says Takaaki Kasuga, lead and senior author. “This is an active area of research, but the proposed alternatives to date haven’t met society’s needs.”

While researching the global need for a plastic substitute, Kasuga and coworkers were inspired by cellulose nanofibers. For example, these ultrasmall fibers help plants maintain rigid yet lightweight structures. In fact, on a pound-for-pound basis, cellulose nanofibers help wood to be—by some metrics—stronger than steel. The ability to tailor the hierarchical nature of such nanofibers has made them an active area of research in synthetic tissue and other bioengineering contexts.

Various techniques are currently available for molding nanofibers into a controlled orientation; i.e., to exhibit anisotropy. However, a simple technique that enables one to mold cellulose nanofibers from the nano- to macroscopic scale, on multiple spatial axes, has long been unavailable. To meet this need, Kasuga and coworkers used electrophoretic deposition to fabricate anisotropic cellulose-nanofiber-based hydrogels and moldings.

There were several especially impressive outcomes of this study. One, cellulose nanofibers were oriented horizontally, randomly, and vertically by simply changing the applied voltage. Two, a multilayer hydrogel was easily prepared with alternating nanofiber orientations, in a manner that’s reminiscent of biological tissue. Three, “we easily prepared complex architectures, such as microneedles and mouthpiece molds,” says Kasuga. “The uniform nanofiber orientation helped suppress hydrogel cracking, and thus resulted in a smooth surface, upon drying.”

The technique used in this study is not limited to cellulose nanofibers. For example, the researchers also used sodium alginate and nanoclay. Thus, multicomponent materials that exhibit controlled nanoscale orientations are also straightforward to prepare. An immediate application of this study is straightforward manufacturing of complex, hierarchical hydrogels and moldings over a wide range of spatial scales. Such ecofriendly hydrogels and moldings will be useful in healthcare, biotech, and other applications—and thus will help alleviate the need for petroleum-based plastics.

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

One-Pot Hierarchical Structuring of Nanocellulose by Electrophoretic Deposition by Takaaki Kasuga, Tsuguyuki Saito, Hirotaka Koga, and Masaya Nogi. ACS Nano 2022, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acsnano.2c06392 Publication Date: October 21, 2022 © 2022 The Authors. Published by American Chemical Society

This paper appears to be open access.

Cellulose nanofiber (CNF) coating protects plants against rust disease

A September 8, 2021news item on ScienceDaily describes some new research into rust disease,

A water-absorbent coat to keep rust away? It may seem counterintuitive but when it comes to soybean plants and rust disease, researchers from Japan have discovered that applying a coating that makes leaf surfaces water absorbent helps to protect against infection.

Caption: Researchers from the University of Tsukuba have found that coating soybean plant leaves with cellulose nanofiber (CNF) gives protection against an aggressive fungal disease. The CNF coating changed leaf surfaces from water repellent to water absorbent, and suppressed pathogen gene expression associated with infection mechanisms, offering resistance to the destructive Asian rust disease. This is the first study to examine CNF application for controlling plant diseases, and it offers a sustainable alternative to managing plant disease.. Credit: University of Tsukuba

A September 7, 2021 University of Tsukuba press release (also on EurekAlert but published September 8, 2021), which originated the news item, describes the disease and proposed solution in more detail,

In a study published this month in Frontiers in Plant Science, researchers from the University of Tsukuba have revealed that coating soybean plant leaves with cellulose nanofiber changes the leaf surface from water repellent to water absorbent and offers resistance against Asian soybean rust.

Rusts are plant diseases that get their name from the powdery rust- or brown-colored fungal spores on the surfaces of infected plants. Asian soybean rust (ASR) is an aggressive disease of soybean plants, causing estimated crop yield losses of up to 90%. ASR is caused by Phakopsora pachyrhizi, a fungal pathogen that requires a living plant host to survive. The timely application of fungicide is currently the only way of controlling ASR in the field. But the use of fungicides can be problematic, resulting in negative environmental effects, increased production costs, and fungicide-resistant pathogens.

“We investigated cellulose nanofiber (CNF) as an alternative method of controlling ASR,” says senior author of the study, Professor Yasuhiro Ishiga. “Specifically, we wanted to know whether coating soybean plant leaves with CNF protected plants against P. pachyrhizi.

Of the available methods for isolating CNF, aqueous counter collision (ACC) has been shown to alter the hydrophilic (water absorbent) and hydrophobic (water repellent) properties of surfaces, switching one to the other. Previous research has indicated that CNF obtained via ACC has higher wettability than CNF isolated by other methods.

“We showed that CNF can change the soybean leaf surface from hydrophobic to hydrophilic,” explains senior author, Professor Yuji Yamashita. “This offers resistance against P. pachyrhizi.”

The team found fewer lesions and significantly reduced formation of P. pachyrhizi appressoria, which are specialized pre-infection structures used to break through the outer surface of the host plant, on CNF-treated leaves compared with control (untreated) leaves. The results also revealed suppressed gene expression linked to the formation of pre-infection structures in P. pachyrhizi on treated versus control leaves.

“In particular, chitin synthase gene expression was suppressed, and P. pachyrhizi needs chitin synthases to form pre-infection structures,” says Professor Ishiga.

This study is the first to investigate the application of CNF for controlling plant diseases in the field, and this technique offers new possibilities for sustainable and eco-friendly management of plant diseases.

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

Covering Soybean Leaves With Cellulose Nanofiber Changes Leaf Surface Hydrophobicity and Confers Resistance Against Phakopsora pachyrhizi by
Haruka Saito, Yuji Yamashita, Nanami Sakata, Takako Ishiga, Nanami Shiraishi, Giyu Usuki, Viet Tru Nguyen, Eiji Yamamura and Yasuhiro Ishiga. Front. Plant Sci., 03 September 2021 DOI: https://doi.org/10.3389/fpls.2021.726565

This paper appears to be open access.

Stronger than steel and spider silk: artificial, biodegradable, cellulose nanofibres

This is an artificial and biodegradable are two adjectives you don’t usually see united by the conjunction, and. However, it is worth noting that the artificial material is initially derived from a natural material, cellulose. Here’s more from a May 16, 2018 news item on ScienceDaily,

At DESY’s [Deutsches Elektronen-Synchrotron] X-ray light source PETRA III, a team led by Swedish researchers has produced the strongest bio-material that has ever been made. The artifical, but bio-degradable cellulose fibres are stronger than steel and even than dragline spider silk, which is usually considered the strongest bio-based material. The team headed by Daniel Söderberg from the KTH Royal Institute of Technology in Stockholm reports the work in the journal ACS Nano of the American Chemical Society.

A May 16, 2018 DESY press release (also on EurekAlert), which originated the news item, provides more detail,

The ultrastrong material is made of cellulose nanofibres (CNF), the essential building blocks of wood and other plant life. Using a novel production method, the researchers have successfully transferred the unique mechanical properties of these nanofibres to a macroscopic, lightweight material that could be used as an eco-friendly alternative for plastic in airplanes, cars, furniture and other products. “Our new material even has potential for biomedicine since cellulose is not rejected by your body”, explains Söderberg.

The scientists started with commercially available cellulose nanofibres that are just 2 to 5 nanometres in diameter and up to 700 nanometres long. A nanometre (nm) is a millionth of a millimetre. The nanofibres were suspended in water and fed into a small channel, just one millimetre wide and milled in steel. Through two pairs of perpendicular inflows additional deionized water and water with a low pH-value entered the channel from the sides, squeezing the stream of nanofibres together and accelerating it.

This process, called hydrodynamic focussing, helped to align the nanofibres in the right direction as well as their self-organisation into a well-packed macroscopic thread. No glue or any other component is needed, the nanofibres assemble into a tight thread held together by supramolecular forces between the nanofibres, for example electrostatic and Van der Waals forces.

With the bright X-rays from PETRA III the scientists could follow and optimise the process. “The X-rays allow us to analyse the detailed structure of the thread as it forms as well as the material structure and hierarchical order in the super strong fibres,” explains co-author Stephan Roth from DESY, head of the Micro- and Nanofocus X-ray Scattering Beamline P03 where the threads were spun. “We made threads up to 15 micrometres thick and several metres in length.”

Measurements showed a tensile stiffness of 86 gigapascals (GPa) for the material and a tensile strength of 1.57 GPa. “The bio-based nanocellulose fibres fabricated here are 8 times stiffer and have strengths higher than natural dragline spider silk fibres,” says Söderberg. “If you are looking for a bio-based material, there is nothing quite like it. And it is also stronger than steel and any other metal or alloy as well as glass fibres and most other synthetic materials.” The artificial cellulose fibres can be woven into a fabric to create materials for various applications. The researchers estimate that the production costs of the new material can compete with those of strong synthetic fabrics. “The new material can in principle be used to create bio-degradable components,” adds Roth.

The study describes a new method that mimics nature’s ability to accumulate cellulose nanofibres into almost perfect macroscale arrangements, like in wood. It opens the way for developing nanofibre material that can be used for larger structures while retaining the nanofibres’ tensile strength and ability to withstand mechanical load. “We can now transform the super performance from the nanoscale to the macroscale,” Söderberg underlines. “This discovery is made possible by understanding and controlling the key fundamental parameters essential for perfect nanostructuring, such as particle size, interactions, alignment, diffusion, network formation and assembly.” The process can also be used to control nanoscale assembly of carbon tubes and other nano-sized fibres.

(There are some terminology and spelling issues, which are described at the end of this post.)

Let’s get back to a material that rivals spider silk and steel for strength (for some reason that reminded me of an old carnival game where you’d test your strength by swinging a mallet down on a ‘teeter-totter-like’ board and sending a metal piece up a post to make a bell ring). From a May 16, 2018 DESY press release (also on EurekAlert), which originated the news item,

The ultrastrong material is made of cellulose nanofibres (CNF), the essential building blocks of wood and other plant life. Using a novel production method, the researchers have successfully transferred the unique mechanical properties of these nanofibres to a macroscopic, lightweight material that could be used as an eco-friendly alternative for plastic in airplanes, cars, furniture and other products. “Our new material even has potential for biomedicine since cellulose is not rejected by your body”, explains Söderberg.

The scientists started with commercially available cellulose nanofibres that are just 2 to 5 nanometres in diameter and up to 700 nanometres long. A nanometre (nm) is a millionth of a millimetre. The nanofibres were suspended in water and fed into a small channel, just one millimetre wide and milled in steel. Through two pairs of perpendicular inflows additional deionized water and water with a low pH-value entered the channel from the sides, squeezing the stream of nanofibres together and accelerating it.

This process, called hydrodynamic focussing, helped to align the nanofibres in the right direction as well as their self-organisation into a well-packed macroscopic thread. No glue or any other component is needed, the nanofibres assemble into a tight thread held together by supramolecular forces between the nanofibres, for example electrostatic and Van der Waals forces.

With the bright X-rays from PETRA III the scientists could follow and optimise the process. “The X-rays allow us to analyse the detailed structure of the thread as it forms as well as the material structure and hierarchical order in the super strong fibres,” explains co-author Stephan Roth from DESY, head of the Micro- and Nanofocus X-ray Scattering Beamline P03 where the threads were spun. “We made threads up to 15 micrometres thick and several metres in length.”

Measurements showed a tensile stiffness of 86 gigapascals (GPa) for the material and a tensile strength of 1.57 GPa. “The bio-based nanocellulose fibres fabricated here are 8 times stiffer and have strengths higher than natural dragline spider silk fibres,” says Söderberg. “If you are looking for a bio-based material, there is nothing quite like it. And it is also stronger than steel and any other metal or alloy as well as glass fibres and most other synthetic materials.” The artificial cellulose fibres can be woven into a fabric to create materials for various applications. The researchers estimate that the production costs of the new material can compete with those of strong synthetic fabrics. “The new material can in principle be used to create bio-degradable components,” adds Roth.

The study describes a new method that mimics nature’s ability to accumulate cellulose nanofibres into almost perfect macroscale arrangements, like in wood. It opens the way for developing nanofibre material that can be used for larger structures while retaining the nanofibres’ tensile strength and ability to withstand mechanical load. “We can now transform the super performance from the nanoscale to the macroscale,” Söderberg underlines. “This discovery is made possible by understanding and controlling the key fundamental parameters essential for perfect nanostructuring, such as particle size, interactions, alignment, diffusion, network formation and assembly.” The process can also be used to control nanoscale assembly of carbon tubes and other nano-sized fibres.

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

Multiscale Control of Nanocellulose Assembly: Transferring Remarkable Nanoscale Fibril Mechanics to Macroscale Fibers by Nitesh Mittal, Farhan Ansari, Krishne Gowda V, Christophe Brouzet, Pan Chen, Per Tomas Larsson, Stephan V. Roth, Fredrik Lundell, Lars Wågberg, Nicholas A. Kotov, and L. Daniel Söderberg. ACS Nano, Article ASAP DOI: 10.1021/acsnano.8b01084 Publication Date (Web): May 9, 2018

Copyright © 2018 American Chemical Society

This paper is open access and accompanied by this image illustrating the work,

Courtesy: American Chemical Society and the researchers [Note: The bottom two images of cellulose nanofibres, which are constittuents of an artificial cellulose fibre, appear to be from a scanning tunneling microsscope. Credit: Nitesh Mittal, KTH Stockholm

This news has excited interest at General Electric (GE) (its Wikipedia entry), which has highlighted the work in a May 25, 2018 posting (The 5 Coolest Things On Earth This Week) by Tomas Kellner on the GE Reports blog.

Terminology and spelling

I’ll start with spelling since that’s the easier of the two. In some parts of the world it’s spelled ‘fibres’ and in other parts of the world it’s spelled ‘fibers’. When I write the text in my post, it tends to reflect the spelling used in the news/press releases. In other words, I swing in whichever direction the wind is blowing.

For diehards only

As i understand the terminology situation, nanocellulose and cellulose nanomaterials are interchangeable generic terms. Further, cellulose nanofibres (CNF) seems to be another generic term and it encompasses both cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF). Yes, there appear to be two CNFs. Making matters more interesting is the fact that cellulose nanocrystals were originally christened nanocrystalline cellulose (NCC). For anyone who follows the science and technology scene, it becomes obvious that competing terminologies are the order of the day. Eventually the dust settles and naming conventions are resolved. More or less.

Ordinarily I would reference the Nanocellulose Wikipedia entry in my attempts to clarify the issues but it seems that the writers for the entry have not caught up to the current naming convention for cellulose nanocrystals, still referring to the material as nanocrystalline cellulose. This means, I can’t trust the rest of the entry, which has only one CNF (cellulose nanofibres).

I have paid more attention to the NCC/CNC situation and am not as familiar with the CNF situation. Using, NCC/CNC as an example of a terminology issue, I believe it was first developed in Canada and it was Canadian researchers who were pushing their NCC terminology while the international community pushed back with CNC.

In the end, NCC became a brand name, which was trademarked by CelluForce, a Canadian company in the CNC market. From the CelluForce Products page on Cellulose Nanocrystals,

CNC are not all made equal. The CNC produced by CelluForce is called CelluForce NCCTM and has specific properties and are especially easy to disperse. CelluForce NCCTM is the base material that CelluForce uses in all its products. This base material can be modified and tailored to suit the specific needs in various applications.

These, days CNC is almost universally used but NCC (not as a trademark) is a term still employed on occasion (and, oddly, the researchers are not necessarily Canadian).

Should anyone have better information about terminology issues, please feel free to comment.