Using the delignification and mecha

Using the delignification and mechanical pressing approaches, Zhu et al. [92] fabricated an anisotropic cellulose nanopaper with fully aligned cellulose nanofibers directly from wood. Figure 10(a) shows a comparison of the tensile stress–strain curves of such a nanopaper and an isotropic nanopaper with ran- dom CNFs [92]. The anisotropic nanopaper with well-aligned CNFs has a mechanical tensile strength (approximately 350 MPa) and toughness (7.38 MJ/m3) that are nearly three times those of a nanopaper with randomly distributed CNFs. The tensile strength (23.2 MPa) of anisotropic nanopaper in the direction perpendicu- lar to the CNF alignment is much smaller than that of the nanopa- per along the CNF alignment direction. When CNFs are parallel distributed in the nanopaper, a maximized number of interfaces exist at which each individual CNF can slide over each other. The interfacial sliding is accommodated by breaking of the hydrogen bonds.