Cellulose nanofiber/carboxymethyl cellulose blends as an efficient coating to improve the structure and barrier properties of paperboard

Abstract

Cellulose nanofibers (CNF) have been suggested in the literature as a potential barrier coating layer for paper and paperboard. However, due to its rheological properties and solids content, the material is difficult to apply to paper at significant coat weight levels. The use of CNF as a coating to improve the structure and barrier properties of paperboard was investigated. Two forms of CNF were used: (1) refiner produced material and (2) material produced with an ultra-fine grinder. Carboxymethyl cellulose (CMC) was used for some samples as an additive. The rheology of these suspensions was characterized. These materials were applied onto the surface of paperboard using a draw-down rod coater in two layers. Scanning electron microscope (SEM) was used to see the coverage of the paper by the CNF layer. Air permeability, water penetration and barrier properties of the samples were characterized. The steady shear viscosity of CNF suspension decreased after the addition of CMC. Although CNF at 2% solid content without CMC could not be spread out onto the surface of paper uniformly, 3% CNF along with CMC was successfully coated on the surface of paper: CMC acts as a dispersant that produces a uniform suspension with minimal flocs. The ground CNF with CMC produced the best samples with good coverage as revealed by SEM images. The results show that the structure and barrier properties of coated paperboards improved considerably by the application of CNF coatings.