[P2-64] Molecular dynamics study on transmission mechanism of torsional deformation in cellulose nanofibers with hierarchical structure
Cellulose nanofiber (CNF) has high strength comparable to steel, and it shows low environmental load during a cycle of production and disposal. Beside it has many excellent properties and functions such as high rigidity, light-weight, flexibility and shape memory effect, so it is expected as a next-generation new material. CNF is a fibrous and nano-sized substance produced by decomposition of bulk-type cellulose which is a main component of plants. Usually it is constituted by many cellulose micro fibrils (CMFs) in which molecular chains of cellulose are aggregated in a crystal structure. It is also possible to make composite material of CNF together with other components, and then a new material with lightweight as well as high strength and high toughness will be realized. In such case, knowledge of mechanical properties for each CMF units is important. Since actual fibrils are complicatedly intertwined, it is also crucial to elucidate the transmission mechanism of force and deformation not only in one fibril but also in between fibrils. Indeed, how the dynamic and hierarchical structure composed of CMFs responds to bending or torsion, which includes gradient of stress and strain, is an interesting issue. However, little is known on torsional characteristics (shear modulus, torsional rigidity, etc.) concerning CMF. In general, in a wire-like structure, it is difficult to enhance torsional rigidity and strength, compared with tensile ones. Therefore, in this study, we try to build a hierarchical model of CNF by multiplying CMF fibers and to conduct molecular dynamics simulation for torsional deformation, by using a hybrid modeling between all-atoms and united-atoms models. First, shear modulus was estimated for one CMF fibril and it showed a value close to the experimental values. In addition, it is revealed that intermolecular hydrogen bonds (HBs) are dynamically changed and the HB mechanism is likely to work as strong resistance in torsional deformation.