Application of cellulose nanofibril (CNF) as coating on paperboard at moderate solids content and high coating speed using blade coater

Abstract

Cellulose nanofibrils (CNFs) have the potential to be applied to paper or plastics to produce a good gas barrier layer. Past work has used CNF at low solids content because high viscosity at higher consistencies is problematic. Efficient coating processes are needed to apply CNF at higher solids and significant coat weights to reduce drying requirement and decrease water-paper interactions. A cylindrical laboratory coater (CLC) is used to coat two different forms of CNF at different solids content in double layers. CNF suspension is applied at moderate solids content and a high coat weight (>10 g/m2) is possible to be obtained using the blade coater. While others have reported the application of CNF at low solids and moderate speeds, this work shows that it is possible to apply CNF at high speeds (10 m/s) and moderate solids. SEM images reveal that a full surface coverage is obtained even at higher solids content especially when carboxymethyl cellulose (CMC) is added to the coating formulation. The results indicate that an increase around 10–20% for tensile index and about 15% for bending stiffness is obtained. A superior grease barrier property is observed in paperboards with a kit number of 12. An increase of over 300% is found for Hercules sizing results. Air resistance of CNF-coated paperboards increases by a significant amount. Additionally, picking resistance of coated sample is improved with increasing the solids content of CNF coating. The contact angle for water droplets decreases for CNF-coated samples over the uncoated paperboards, however for diiodo-methane (a non-polar liquid) an increase in contact angle is observed.