Natural polysaccharides may be a viable alternative to fossil resources.
Polysaccharides (*1) are widely distributed in nature and are known to be abundant biomass resources. Accordingly, natural polysaccharides, such as cellulose (*2) and chitin (*3), can be regarded as renewable functional alternatives to fossil resources. They are structurally composed of monosaccharide residues linked through glycosidic linkages, which have very complicated structures, owing not only to the variety of monosaccharide structures, but also to the differences in specificities of the linkages. Besides traditional uses, therefore, new material applications of polysaccharides are still a challenging research topic. Our research group investigates the development of new polysaccharide-based functional materials by means of hierarchically controlled nano-assemblage (*4) of polymeric chains. The efficient use of natural polysaccharides as components in functional materials will lead to the development of new green and sustainable materials.
New polysaccharide functional materials are fabricated through controlled nano-assembling.
An attempt is made to fabricate chitin nanofibers (*5) by the self-assemblage of chitin molecules through appropriate procedures (Figure 1). Chitin generally forms large aggregates in water, while its nanofibers are dispersed well in water, leading to new practical applications such as the creation of biomaterials. A cellulose composite material with elastic property is fabricated by combining with ionic liquid (*6) (Figure 2). This approach will be applied to produce elastic cellulose plastics in the future.
1: Polysaccharides are structurally composed of monosaccharide residues linked through glycosidic linkages, which have very complicated structures owing not only to the variety of monosaccharide structures but also to the differences in stereo- and regio-types of glycosidic linkages.
2: Cellulose is a polysaccharide composed of glucose repeating units and is the most abundant organic resource on the earth. Because of its highly crystalline structure, it acts as a structural material, as in the cell wall in wood, but exhibits poor solubility and is difficult to process.
3: Chitin is a polysaccharide present in crustacean shells of crab and shrimp and is the second most abundant organic resource after cellulose. As with cellulose, it has a highly crystalline nature, leading to poor processing ability and solubility.
4: Polymers hierarchically assemble in nano-scales to construct larger structures, leading to new functions. As is characteristic of polymers, multiple assembled structures from a sole polymer can be obtained by different procedures to show several properties and functions.
5: Nanofibers are fibrous materials at a nano-scale, which can be fabricated by controlled assemblage of polymers. Nanofibers show outstanding characteristics, for example, cellulose nanofiber exhibits light-weight, high-strength, and thermal expansion on par with glass.
6: Salt can be used to make an ionic liquid, in which the ions are poorly coordinated, which remain liquid below 100°C. These ionic liquids are known to act as solvents for poorly soluble materials.