Cellulose nanofibrils offer interesting potential as a native fibrous constituent of mechanical performance exceeding the plant fibers in current use for commercial products. In the present study, wood nanofibrils are used to prepare porous cellulose nanopaper of remarkably high toughness. Nanopapers of different porosities and from nanofibrils of different molar mass are prepared. Uniaxial tensile tests are performed and structure-property relationships are discussed. The high toughness of highly porous nanopaper is related to the nanofibrillar network structure and high mechanical nanofibril performance. Also, molar mass correlates with tensile strength. This indicates that nanofibril fracture controls ultimate strength. Furthermore, the large strain-to-failure means that mechanisms, such as interfibril slippage, also contributes to inelastic deformation in addition to deformation of the nanofibrils themselves.

Free energy was measured for the surface of regular aligned closest hexagonal packed −CF3 groups. n-Perfluoroeicosane was vapor deposited onto glass, which gave epitaxially grown single-like crystallites with their molecular axes perpendicular to the glass surface. The dynamic contact angle of water on its surface was 119°, which corresponds to a surface free energy of 6.7 mJ/m2. This value is considered to be the lowest surface free energy of any solid, based on the hexagonal closed alignment of −CF3 groups on the surface.

An all-cellulose composite, in which both the fibers and the matrix are cellulose, was prepared by distinguishing the solubility of the matrix cellulose into the solvent from that of the fibers through pretreatment. The structure, mechanical, and thermal properties of this composite were investigated using an X-ray diffraction, a scanning electron microscope, a tensile test, and dynamic viscoelastic and thermomechanical analyses. The tensile strength of uniaxially reinforced all-cellulose composite was 480 MPa at 25 °C, and the dynamic storage modulus was as high as 20 GPa at 300 °C. These were comparable or even higher than those of conventional glass-fiber-reinforced composites. In addition, a linear thermal expansion coefficient was about 10-7 K-1. This all-cellulose composite shows substantial advantages, that is, it is composed of sustainable resources, there is less interface between the fiber and the matrix, it possesses excellent mechanical and thermal performance during use, and it is biodegradable after the service.