Effect of overlapping cellulose nanofibrils and nanoclay layers on mechanical and barrier properties of spray-coated papers

This work evaluates the effect of spraycoating papers using cellulose nanofibrils (CNFs) and nanoclay (NC) on the mechanical and barrier properties for application such as reinforced packaging bags. Sack kraft papers of 60 g m(-2) (C60) were coated with combinations of CNFs and CNFs + NC, varying the number of layers on the internal face (IF) and external face (EF) of the paper. Their properties were compared to uncoated sack kraft papers with basis weight of 60 g m(-2) (C60), 80 g m(-2) (C80) and 120 g m(-2 )(C120). The amount of CNF/NC deposited was similar to 20 g m(-2) while the CNF layer deposited was similar to 10 g m(-2) on the sack papers. Increase in the number of layers deposited decreased the water vapor transmission rate (WVTR) compared to C60. CNF layer had lower contact angles on the coated papers than CNF/NC layer. The coated papers also showed a 44-66% increase in tensile index when compared to C120. Papers coated with 2 layers of CNFs and 1 layer of CNFs /NC achieved the same tensile index as C120 and the layers also resulted in higher values of Young's modulus (38-56%) when compared to C60. Spray-coating, with the appropriate layers, improved the mechanical and barrier properties of the coated papers, and is a possible alternative to producing papers with lower basis weight and using renewable raw materials. Additionally, the mixture of two hydrophilic components, such as nanofibrils and NC can result in a coating with more hydrophobic characteristics.