セルロースナノファイバーのねじり変形に関する分子動力学解析

―階層構造にともなう変形機構の解明―

抄録

A composite material containing nano-sized cellulose (or cellulose nanofiber: CNF) which is ecologically friendly and derived from abundant plants attracts much attention in material engineering. However, it is necessary to elucidate mechanical properties in the basic structure of cellulose, that is, CMF (cellulose micro-fibril) unit. Since actual fibrils of CNF take the form of aggregate comprising many elements and they are intertwined complicatedly, it is crucial to clarify transmission mechanism of force and deformation between fibrils. Therefore, in this study, we create a hierarchical structure model of multiplied CNF structures and simulate it using molecular dynamics method, especially as for torsional deformation. First, a hierarchical structure of CNF is generated by colliding two 5-layered crystalline CMFs. Next, in applying torsional deformation to one component of CMF, we observe how the local deformation transforms to the other. According to the stress-strain diagram obtained during torsional simulation, almost complete stress transmission is confirmed for very small strain, but, as the deformation increases, the hydrogen bonding between these CMFs is generally weakened and no stress transmission is done. The shape of CMF without torsional load spontaneously returns to its original one, which is already recognized as the behavior of superelasticity peculiar to CMF. It is also found that, between two CMFs, a torsional moment transforms into a bending moment.