Facile preparation of optically transparent and hydrophobic cellulose nanofibril composite films

• A facile and scalable procedure to produce cellulose nanofibril/epoxy nanocomposite by lamination was successfully obtained.
• The composite films displayed excellent mechanical strength, thermal stability, and optical transmittance.
• Lamination of epoxy layer contributes to the prevention of individual cellulose nanofibrils from moisture and water attack.
• The resultant films are promising alternative for advanced package and visual display, particularly for flexible electronics substrates.

Cellulose nanofibril (CNF) and epoxy nanocomposites with high visible light transmittance and low water sensitivity were manufactured by laminating thin layers of epoxy resin onto CNF films prepared through, pressurized filtration in combination with oven drying. Scanning Electron Microscopy (SEM) studies suggest that the resin component bonded to the CNF substrate well. Atomic Force Microscopy (AFM) observation reveals that the resin lamination led to smoother film surface, which helped enhance UV–vis transmittance. The addition of epoxy resin had little effect on the static and dynamic mechanical strength. However, crystalline and interconnected CNFs significantly reduced the loss factor and shifted the glass transition of composite to a high temperature. Compared to pure CNF films, the CNF/epoxy composites showed a 20% improved transparence in the visible light range. The CNF/epoxy composites demonstrated a sufficient water resistance. This composite film could be considered as a potential substrate material in the application of flexible electronics substrates.