Study on the Multilayer Barrier Coating Using Cellulose Nanofibrils and Internal Sizing Agent

In this study, we tried to develop techniques to increase coat weight and improve water resistance at a lower number of multilayer barrier coatings with anionic and cationic cellulose nanofibrils (CNFs), which has been reported in previous research. The concentration of CNF slurry was adjusted to increase the coat weight, while alkyl ketene dimer (AKD) was added as an internal sizing agent to the anionic CNF slurry to impart hydrophobicity to the CNFs. After the preparation of CNF slurries, the multilayer barrier coating was applied on never-size base paper. The coat weight, air permeability, and Cobb size degree of the barrier-coated paper were subsequently measured, and the surface of the paper was analyzed via SEM. The coat weight and air permeability of the paper coated four times with CNF slurry at 1.4% concentration were similar to those of the paper coated six times with CNF slurry at 1.0% concentration. In addition, the Cobb size degree of the barrier-coated paper decreased as the AKD addition to anionic CNF at a concentration of 1.4% increased linearly. However, when the addition level of AKD increased more than 5.0%, the Cobb size degree of the barrier-coated paper increased due to the uneven distribution of AKD. Therefore, multilayer barrier coating can be carried out effectively with cationic and anionic CNFs at high concentrations, and AKD improves the water resistance of barrier-coated paper.