Japan a world leader in cellulose nanofiberGreen nanomaterial seven times stronger than steel but 1/5 the weight August 05, 2014 Hiroyuki Yano This article first appeared in Japanese on JBpress on June 25. You can read it here. Nanotechnology research has leapt forward over the past decade due to the vast range of potential applications across scientific fields as diverse as surface science, molecular biology, and semiconductor physics. One such technology involves the use of cellulose nanofiber, a biological material found inside plant cell walls. Professor Hiroyuki Yano, a leading figure in cellulose nanofiber research, discusses the exciting possibilities for this amazing material and why Japan, with its rich forests and technical know-how, is a world leader in this promising field. At the inaugural conference of the Nanocellulose Forum held in Tokyo on June 9, 2014, Midori Matsushima, Japans Vice Minister of Economy, Trade and Industry, congratulated the 300 attendees in her address, saying, There are infinite possibilities for cellulose nanofiber. We should make this a national project and fully utilize Japans rich forest resources. Stronger and lighter than steel, the miracle material born from plant fiber Figure 1: Cellulose nanofibers from cell walls in wood (Image courtesy of Dr. Awano, Kyoto University) Cellulose nanofiber weighs only one fifth the weight of steel, yet is seven to eight times stronger, with a width of between 4 and 20nm (nanometers) (see Figure 1). With a linear thermal expansion that is one fiftieth that of glass, it is comparable to quartz glass. Described in this way, one may receive the impression that this fiber is extremely rare, but in fact it is believed to account for about half of the worlds woody biomass – a weight of approximately 1.8 trillion tons. In plant cells, cellulose nanofibers act as the structure while lignin serves as the concrete that supports them. If this concrete layer is removed, the exposed cellulose fibers on each plant cell can be made into pulp, the raw material for paper. With the development of electron microscopy that made it possible to glimpse the nanoworld, it wasnt long before scientists discovered that the plant cell wall is made up of uniform, crystalline nanofibers. According to an X-ray analysis conducted by Dr. Sakurada and his team from Kyoto University, the crystals modulus of elasticity (i.e., how much pressure is required to deform it) is estimated to be 140GPa (gigapascals), about two thirds of that of steel. 30 years ago, the Pulp and Paper Research Institute of Canada reported that the tensile strength of a single sheet of pulp is 1.7GPa (five times that of steel panels on automobiles). At around the same time, a study of different types of timber used to make musical instruments reported that the alignment of cellulose nanofibers within cell walls determined the timbers suitability. Despite these findings, research for the extraction from woody biomass and utilization of nanofibers did not become commonplace until nanotechnology became prominent in the first decade of the 2000s. In fact, the history of nanomaterials research is really only about ten years old. Yet within these ten years, advances in nanomaterials have been remarkable. With impressive properties such as its light weight, high strength, and low thermal expansion, cellulose nanofibers are being hailed as the next generation large-scale industrial material or the green nanomaterial, with academic papers and patent applications skyrocketing since 2004. A high-performance multipurpose material The main players in the research of cellulose nanofibers are countries with rich forest resources: Northern Europe, North America, Japan, and more recently, China. With Finland, Canada and the U.S. taking the lead in the debate surrounding international standardization from 2011, progress in cellulose nanofiber research has become a race among nations. A wide range of developments are now underway that take advantage of the many properties of cellulose nanofibers and cellulose nanocrystals (crystalline materials with high purity cellulose made from the treatment of pulp or cellulose nanofibers with concentrated sulfuric acid), including high specific surface area, edibility, light weight, low thermal expansion, high strength, biodegradability, and biocompatibility. Since cellulose nanofibers are thinner than the wavelength of visible light (400-800nm), they do not cause scattering and as such can be use to reinforce materials such as acrylic resin and epoxy resin without compromising their transparency. Figure 2 illustrates two types of transparent fiber-reinforced materials that have low thermal expansion, high strength, and most importantly, flexibility, and that exemplify some of the current research and development into organic EL (electroluminescent) displays and transparent substrates for organic membranes in solar cells. Figure 2: Transparent reinforced cellulose nanofiber material (left), substrate for a organic EL device (right) (Photo credit: author) A film made of cellulose nanofibers disintegrated to a width below 10nm through TEMPO (abbreviation for (2,2,6,6- tetramethylpiperidin-1-yl) oxidanyl)-mediated oxidation has high transparency. Since they exhibit an oxygen gas permeability of less than one hundredth that of PVC (polyvinyl chloride) and PET (polyethylene terephthalate) while maintaining an adequate degree of moisture permeability, cellulose nanofibers are being studied as a potential coating material for packaging containers. Many studies testing the lightweight and high-strength characteristics of nanofibers for their use in structural applications are also ongoing. For example, when a sheet of nanofibers is injected with a phenolic resin, after lamination and curing the sheet becomes as strong as steel while maintaining only one fifth steels weight and a fiber content of 90 percent. Furthermore, when chemically modified cellulose nanofibers are mixed at 10 percent with thermoplastic, the strength increases another two to three times. This property is highly sought-after in the transportation industry, including automobiles, that requires lightweight and high-strength structural materials. Steady progress is also being made in development in the areas of: paper strengthening and surface-smoothing; food and cosmetic additives; medical applications such as artificial blood vessels and tendons; catalyst carriers; filter materials; and separators for secondary batteries. By taking advantage of the natural interaction and structure between lignin and cellulose nanofibers inside cell walls, it is possible to develop increasingly sophisticated yet inexpensive materials. Japans harmony with nature an advantage in biomaterials development We are in an age where there is a high demand for green innovation based on materials derived from plants, and cellulose nanofiber is an ideal candidate. The key to green innovation is to respect living things and borrow their power by utilizing materials that have been produced by nature through environmentally-friendly processes. In this sense, we owe our research and the use of woody biomass, including cellulose nanofibers, to their original creator: the trees themselves. When using cellulose nanofibers, it is important to keep in mind that the biological structure and properties of the material are the result of centuries of evolution. By changing the shape of the material without compromising its natural state, it is possible to produce high-performance, energy-saving materials. When it comes to making things, the attitude of maintaining harmony with nature is one that has been cultivated in Japan since long before Western civilization reached our shores. In this land with its four distinct seasons, this unique mindset is deeply ingrained. By cherishing this attitude and producing advanced biomaterials, Japan will be able to increase its presence globally. Certainly, with 70 percent of the country composed of forests, Japan holds both the resources and knowledge to lead in cellulose nanofiber research. The author is a Doctor of Agriculture and a professor at Kyoto Universitys Research Institute of Sustainable Humanosphere, and is a leader in wood materials research. He is a member of The Society of Materials Science, Japan, the Japan Wood Research Society and the Cellulose Society of Japan, and has received awards from the latter two.
Posted on: Wed, 06 Aug 2014 02:21:51 +0000
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