Thin film formation of cellulose nanofiber and its physical properties

Cellulose nanofiber (CNF) is known to have high mechanical strength, high Young's modulus, optical transparency, low thermal expansion coefficient and low density, which are beneficial for flexible display substrates and optical films. The purposes of this study is to fabricate ultrathin CNF film and to explore its physical properties. CNF suspension is extracted by 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) oxidation combined with aqueous counter collision (ACC) treatment from bleached hardwood pulp. The CNF suspension is cast on a thin positive photoresist (PR) layer by a doctor blade casting method followed by removing PR layer and drying on a polytetrafluoroethylene (PTFE) sheet to obtain ultrathin CNF film. Morphology of ultrathin CNF film is characterized by atomic force microscopy and the thickness of the film was characterized by FE-SEM. Transparency and birefringence of the prepared ultrathin CNF film are tested by using an UV-visible spectrometer and a digital camera. The piezoelectric response microscopy (PFM) is utilized to analysis the piezoelectric properties of ultrathin CNF film.