Cellulose nanofiber orientation in nanopaper and nanocomposites by cold drawing.

To exploit the mechanical potential of native cellulose fibrils, we report on the preparation of nanopaper with preferred orientation of nanofibrillated cellulose (TEMPO-NFC) by cold drawing. The preparation route is papermaking-like and includes vacuum filtering of a TEMPO-oxidated NFC water dispersion, drawing in wet state and drying. The orientation of the fibrils in the nanopaper was assessed by AFM and wide-angle X-ray diffraction analysis, and the effect on mechanical properties of the resulting nanopaper structure was investigated by tensile tests. At high draw ratio, the degree of orientation is as high as 82 and 89% in-the-plane and cross-sectional planes of the nanopaper, respectively, and the Young's modulus is 33 GPa. This is much higher than mechanical properties of isotropic nanopaper. The cold drawing method can be also applied to NFC nanocomposites as demonstrated by preparation of TEMPO-NFC/hydroxyethyl cellulose (HEC) nanocomposites. The introduction of the soft HEC matrix allows further tailoring of the mechanical properties.