The influence of barrier pigments in waterborne barrier coatings on cellulose nanofiber layers

Layers of cellulose nanofibers (CNF) have great potential to be used in food packaging applications because of their oxygen and grease barrier properties. However, because of their sensitivity to moisture, they likely will need to be used in a layered structure with water vapor barrier layers. Waterborne barrier coatings (WBBC) have the potential to provide this water vapor barrier, but their performance on paper with a CNF layer has not been described in the literature. Paper that had a CNF layer was coated with three different WBBC with various levels of two different barrier pigments to improve the water vapor barrier properties of these systems. The effective diffusion coefficient of these systems was obtained by fitting the data to a two-layer diffusion model. A finite element code was used to predict the flux rate of water vapor through the barrier layers in the presence of a barrier pigment. The dangers of samples “blocking” in production have been tested as well as grease barrier properties. The presence of the CNF layer on paper is shown to improve the performance of the water vapor barrier layer, in some cases, by a factor of six. Adding barrier pigment to the WBBC improves barrier properties at low concentration by 15%, but as the concentration of pigment increases, the barrier properties decrease. The water vapor transmission rate does not decrease to the same order of magnitude as expected from simple theoretical models and the finite element calculations. This result likely is linked to fine bubbles in the coatings that are hard to remove or other defects that are generated during coating or drying. Barrier pigments remove concerns around blocking. All samples had good grease barrier properties.