Column：Special Contribution for the Establishment of Nanocellulose Japan (NCJ)
What is Nanocellulose ?
Vice Chairman of Nanocellulose Japan
Dr. Akira Isogai
(University Professor, The University of Tokyo)
Under the new name of Nanocellulose Japan (NCJ), an initiative to promote the further practical application of nanocellulose has been launched under the cooperation of the all-Japan system. This move is both timely and very significant. NCJ is now recruiting members who are interested in our project. We are looking forward to participation, not only from those who are engaged in research and development of cellulose-related materials, but also from those who have been involved in research and development of petroleum and inorganic materials and are now interested in nanocellulose, as well as from a wide variety of fields such as health, medicine, economics and sociology.
Nanocellulose has a wide variety of structures and properties. Slight differences in structure and characteristics have a great impact on the quality, stability, safety, environment, and price of products containing nanocellulose. Therefore, in order to promote the practical application of nanocellulose, it is essential to obtain information on this material from various viewpoints. Considering that nanocellulose is a novel bio-based material that can be reproduced, further basic and applied research results must be accumulated before the whole picture of this material can be elucidated. Many reports have been published by researchers around the world on the preparation methods of many nanocelluloses, their nanostructures, properties, functions, and research on material development. It is difficult to discuss them in detail here. The following is an overview of the research findings, which are recognized as a common issue for nanocelluloses.
The familiar wood cellulose fibers for paper manufacturing are about 0.03 mm wide and 1 to 3 mm long, and are manufactured by pulping wood chips and then bleaching them. In all land plants, including trees, about 40% of their dry weight is made up of a linear polysaccharide called cellulose. Twenty to forty cellulose molecules are regularly bundled together to form crystalline “cellulose microfibrils”. The width of cellulose microfibrils is about 3 nm and the length reaches several micrometers. Cellulose microfibrils are superfine and uniform in width. The width of cellulose microfibrils is about 10,000 times thinner than that of wood cellulose fibers. It is known that cellulose microfibrils are rigid, having a crystalline modulus of approximately 140 GPa. In the cell walls of trees, cellulose microfibrils act like rebar and form natural nanocomposites with hemicellulose and lignin components. The high-strength nanocomposite structure, which is contributed by the crystalline structure of nanocellulose, enables trees to withstand wind and rain, resist gravity, and maintain their longevity.
Nanocellulose is prepared by “disintegrating” plant cellulose fibers in the presence of water by exerting a shearing force. Nanomaterials are defined as materials having any of the three dimensional sizes (length, width, and height) in the nano-region (1-100 nm). Thus, nanocelluloses refer to plant cellulose fibers whose width is in the nano-region. Cellulose microfibrils are the smallest unit of cellulose fibers, with a width of about 3 nm. However, when considering the entirety of what is recognized as nanocelluloses, their width is distributed between 3 and 100 nm. Assuming that a 100-nm wide nanocellulose has a square cross section, several hundred cellulose microfibrils remain in a bundle without refinement. The surface area of nanocellulose with a width of about 3 nm is several hundred times larger than that of nanocellulose with a width of about 100 nm. Naturally, the properties, functions, and compounding effects with polymers, etc., are completely different between the two types of fibers.
In the case of 3 nm wide nanocellulose, the water dispersion is transparent because its width is less than the wavelength of light (400～900 nm) . On the other hand, if nanocellulose with a width of several tens of nm forms a network structure (entangled structure) in water that is larger than the wavelength of light, light is reflected there. Therefore, even when the concentration of nanocellulose is identical, the water dispersion may be translucent or white. Even taking only the dispersion state in water, the width of nanocellulose are of various sizes, and the appearance of the dispersion varies depending on the value of the width. When the nanocellulose fibers are dried or complexed with other components, the width values may change further. Therefore, there is a need to develop a method to accurately measure the width and width distribution of nanocellulose in various conditions. Unfortunately, there are currently no analytical methods or equipment that can meet such demands.
As described above, cellulose nanocellulose species are diverse in shape alone. In addition, when the chemical structure, molecular weight, and diversity of components of nanocellulose are included, there are many fundamental issues that need to be resolved in order to classify and distinguish between nanocellulose species in an academic manner. Furthermore, taking into account that these issues may depend on the purpose of use and application, a simple and accurate evaluation method for nanocellulose that can be adapted to various situations is required.
To address these challenges, it is necessary to promote both basic research on nanocellulose and research and development for its practical application. As a platform for solving these issues, NCJ has started with an important mission. In Japan, research and development of various types of cellulose nanocellulose has been carried out. For some of them, pilot and full-scale productions have been already started. The practical application of this technology to various high-functional materials has also been advanced. Recently, the creation of a concept car using nanocellulose was accomplished with the cooperation of industry, government, and academia, and this is one of the realization of a practical application project. Since nanocellulose is a novel bio-based nanomaterial with excellent properties and functions and is derived from wood resources that can be reproduced, expanding the qualitative and quantitative use of nanocellulose will lead to revitalization of the domestic forest industry and promote the fixation and reduction of carbon dioxide in the atmosphere. Therefore, advancing the research and development of nanocellulose will help to solve the problems faced by the world, such as global warming, climate change, environmental and resource problems, and microplastic problems. Japan, where basic, applied and practical research on nanocellulose is flourishing, is in a position to take the lead in solving the above problems. NCJ is determined to tackle various issues related to the field of nanocellulose. Your support and cooperation are greatly appreciated.
The hierarchical structure that forms the tree:
Constructed from cellulose molecules via cellulose microfibril structure
(Prepared by the Nanocellulose Forum, 2016)