Tag Archives: Shu-Hong Yu

Bacterial cellulose nanofibers made strong and tough

Despite all the promise that nanocellulose offers, scientists don’t seem to have found significant applications for the material . In the software industry, they used to call it ‘a killer app’, i.e., an application everyone would start using (e.g. Facebook or Google) thereby making much money for its developer(s)..

This July 31, 2019 news item on phys.org describes research that may help scientists develop a nanocellulose ‘killer app’,

High-performance biomass-based nanocomposites are emerging as promising materials for future structural and functional applications due to their environmentally friendly, renewable and sustainable characteristics. Bio-sourced nanocelluloses [sic] (a kind of nanofibers [sic]) obtained from plants and bacterial fermentation are the most abundant raw materials on earth. They have attracted tremendous attention recently due to their attractive inherent merits including biodegradability, low density, thermal stability, global availability from renewable resources, as well as impressive mechanical properties. These features make them appropriate building blocks for spinning the next generation of advanced macrofibers for practical applications.

In past decades, various strategies have been pursued to gain cellulose-based macrofibers with improved strength and stiffness. However, nearly all of them have been achieved at the expense of elongation and toughness, because strength and toughness are always mutually exclusive for man-made structural materials. Therefore, this dilemma is quite common for previously reported cellulose-based macrofibers, which greatly limited their practical applications.

In a new article published in the National Science Review, Recently, a bionics research team led by Prof. Yu Shuhong from the University of Science and Technology of China (USTC) sought an inspiration to solve this problem from biological structures. …

A July 31, 2019 Science China Press news release on EurekAlert, which originated the news item, provides a few moretechnical details,

… They found that the widespread biosynthesized fibers, such as some plant fibers, spider silk and animal hairs, all have some similar features. They are both strong and tough, and have hierarchical helical structures across multiple length scales with stiff and strong nanoscale fibrous building blocks embedded in soft and energy dissipating matrices.

Inspired by these structural features in biosynthesized fibers, they presented a design strategy to make nanocellulose-based macrofibers with similar structural features. They used bacterial cellulose nanofibers as the strong and stiff building blocks, sodium alginate as the soft matrix. By combining a facile wet-spinning process with a subsequent multiple wet-twisting procedure, they successfully obtained biomimetic hierarchical helical nanocomposite macrofibers, and realized impressive improvement of their tensile strength, elongation and toughness simultaneously as expected.

This achievement certifies the validity of their bioinspired design and provides a potential route for further creating many other strong and tough nanocomposite fiber materials for diverse applications.

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

Bioinspired hierarchical helical nanocomposite macrofibers based on bacterial cellulose nanofibers by Huai-Ling Gao, Ran Zhao, Chen Cui, Yin-Bo Zhu, Si-Ming Chen, Zhao Pan, Yu-Feng Meng, Shao-Meng Wen, Chuang Liu, Heng-An Wu, Shu-Hong Yu. National Science Review, nwz077, https://doi.org/10.1093/nsr/nwz077 Published: 21 June 2019

This paper appears to be open access.

Wooden supercapacitors: a cellulose nanofibril story

A May 24, 2018 news item on Nanowerk announces a technique for making sustainable electrodes (Note: A link has been removed),

Carbon aerogels are ultralight, conductive materials, which are extensively investigated for applications in supercapacitor electrodes in electrical cars and cell phones. Chinese scientists have now found a way to make these electrodes sustainably. The aerogels can be obtained directly from cellulose nanofibrils, the abundant cell-wall material in wood, finds the study reported in the journal Angewandte Chemie (“Wood-Derived Ultrathin Carbon Nanofiber Aerogels”).

A May 24, 2018 Wiley Publications press release, which originated the news item, explains further,

Supercapacitors are capacitors that can take up and release a very large amount of energy in a very short time. Key requirements for supercapacitor electrodes are a large surface area and conductivity, combined with a simple production method. Another growing issue in supercapacitor production–mainly for smartphone and electric car technologies–is sustainability. However, sustainable and economical production of carbon aerogels as supercapacitor electrode materials is possible, propose Shu-Hong Yu and colleagues from the University of Science and Technology of China, Hefei, China.

Carbon aerogels are ultralight conductive materials with a very large surface area. They can be prepared by two production routes: the first and cheapest starts from mostly phenolic components and produces aerogels with improvable conductivity, while the second route is based on graphene- and carbon-nanotube precursors. The latter method delivers high-performance aerogels but is expensive and non-environmentally friendly. In their search for different precursors, Yu and colleagues have found an abundant, far less expensive, and sustainable source: wood pulp.

Well, not really wood pulp, but its major ingredient, nanocellulose. Plant cell walls are stabilized by fibrous nanocellulose, and this extractable material has very recently stimulated substantial research and technological development. It forms a highly porous, but very stable transparent network, and, with the help of a recent technique–oxidation with a radical scavenger called TEMPO–it forms a microporous hydrogel of highly oriented cellulose nanofibrils with a uniform width and length. As organic aerogels are produced from hydrogels by drying and pyrolysis, the authors attempted pyrolysis of supercritically or freeze-dried nanofibrillated cellulose hydrogel.

As it turns out, the method was not as straightforward as expected because ice crystal formation and insufficient dehydration hampered carbonization, according to the authors. Here, a trick helped. The scientists pyrolyzed the dried gel in the presence of the organic acid catalyst para-toluenesulfonic acid. The catalyst lowered the decomposition temperature and yielded a “mechanically stable and porous three-dimensional nanofibrous network” featuring a “large specific surface area and high electrical conductivity,” the authors reported.

The authors also demonstrated that their wood-derived carbon aerogel worked well as a binder-free electrode for supercapacitor applications. The material displayed electrochemical properties comparable to commercial electrodes. The method is an interesting and innovative way in which to fabricate sustainable materials suitable for use in high-performance electronic devices.

This is the first time I’ve seen work on wood-based nanocellulose from China. Cellulose according to its Wikipedia entry is: ” … the most abundant organic polymer on Earth.” For example, there’s more cellulose in cotton than there is wood. So, I find it interesting that in a country not known for its forests, nanocellulose (in this project anyway) is being derived from wood.

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

Wood‐Derived Ultrathin Carbon Nanofiber Aerogels by Si‐Cheng Li, Bi‐Cheng Hu, Dr. Yan‐Wei Ding, Prof. Hai‐Wei Liang, Chao Li, Dr. Zi‐You Yu, Dr. Zhen‐Yu Wu, Prof. Wen‐Shuai Chen, Prof. Shu‐Hong Yu. Angewandt Chemie First published: 23 April 2018 DOI: https://doi.org/10.1002/anie.201802753

This paper is behind a paywall.

Bacterial cellulose could suck up pollutants from oil spills

Who doesn’t love a cellulose story, especially when it could involve cleaning up oil spills? The Feb. 26, 2013 news item on phys.org titled, Airy but thirsty: Ultralight, flexible, fire-resistant carbon nanotube aerogels from bacterial cellulose, highlights some work being done in China,

They can absorb vast amounts of oil or organic compounds, yet they are nearly as light as air: highly porous solids made of a three-dimensional network of carbon nanotubes. In the journal Angewandte Chemie, Chinese scientists have now introduced a simple technique for the production of these ultralight, flexible, fire-resistant aerogels. Their method begins with bacterial cellulose as an inexpensive starting material. Their fibrous lightweights can “suck” organic contaminants from polluted water and could possibly be used as pressure sensors.

The researchers [led by Shu-Hong Yu at the Hefei National Laboratory for Physical Sciences at Micrscale (HFNL), Univeristy of Science and Technology of China] trimmed off small pieces of the tangled cellulose nanofibers. These were freeze-dried and then pyrolyzed at 1300 °C under argon. This converts the cellulose into graphitic carbon. The density decreases but the network structure remains intact. The result is a black, ultralight, mechanically stable aerogel. Because it is porous and highly hydrophobic, it can adsorb organic solvents and oils—up to 106 to 312 times its own weight. It draws oil out of an oil/water mixture with high efficiency and selectivity, leaving behind pure water. This makes the new aerogel an ideal candidate for cleaning up oil spills or sucking up nonpolar industrial pollutants. The absorbed substances can easily be removed from the gel through distillation or combustion, allowing the gel to be used again.

There’s more about the work and its possible applications at physorg.com or, if you have access behind the paywall, here’s a citation and a link to the research article,

Ultralight, Flexible, and Fire-Resistant Carbon Nanofiber Aerogels from Bacterial Cellulose by Zhen-Yu Wu, Chao Li, Dr. Hai-Wei Liang, Prof. Dr. Jia-Fu Chen, Prof. Dr. Shu-Hong Yu. Angewandte Chemie International Edition, Volume 52, Issue 10, pages 2925–2929, March 4, 2013.

Here’s an image which illustrates the aerogels’ ability to suck up an organic solvent and explains some of the excitement,

Thirsty fibers: The aerogels described in the title can be fabricated in large scale by using a low-cost biomass, bacterial cellulose, as a precursor, which can be produced at industrial level in a microbial fermentation process. The carbon nanofiber aerogels (black pieces in picture) exhibit superior absorption capacity for organic solvents (red solution) and high potential for pressure sensing. [downloaded from http://onlinelibrary.wiley.com/doi/10.1002/anie.201209676/abstract;jsessionid=3EFB4241C0083135A6E657808F5410E5.d03t04]

Thirsty fibers: The aerogels described in the title can be fabricated in large scale by using a low-cost biomass, bacterial cellulose, as a precursor, which can be produced at industrial level in a microbial fermentation process. The carbon nanofiber aerogels (black pieces in picture) exhibit superior absorption capacity for organic solvents (red solution) and high potential for pressure sensing. [downloaded from http://onlinelibrary.wiley.com/doi/10.1002/anie.201209676/abstract;jsessionid=3EFB4241C0083135A6E657808F5410E5.d03t04]