Continuous roll-to-roll fabrication of transparent cellulose nanocrystal (CNC) coatings with controlled anisotropy

Cellulose nanocrystals (CNCs) can impart desirable barrier properties in film packaging applications; however, commercial production of these materials is inhibited by the absence of a large-scale manufacturing process for producing CNC coatings. To fill this knowledge gap, a potential large-scale manufacturing process, roll-to-roll gravure printing, for cellulose nanocrystal coating on a flexible polyethylene terephthalate substrate has been described in this work. Processing parameters which control the coating structure and properties were examined. For a given gravure roll, gravure speed, substrate speed, and ink viscosity were determined to be the most important parameters that control the liquid transfer from the ink bath to the substrate, which determined the coating thickness (2–6 µm). After successful fabrication, CNC coating adhesion was investigated with a crosshatch adhesion test. The adhesive strength of the CNC coating was correlated with coating thickness, and the maximum coating strength was observed for the lowest coating thickness. Coatings were characterized using atomic force microscopy and UV–Vis spectroscopy. Finally, the crystalline domain arrangement of coatings was determined for coatings made from three different CNC concentrations, and the effect of viscosity on CNC alignment was explained by variation of shear rate, which was controlled by the micro-gravure rotation.