Structural properties of coated papers with cellulosic nanofibres using different metering systems and drying technologies

Cellulose nanofibres (CNFs) can improve the quality of cardboard packaging. This work evaluates the ability of CNFs to impart barrier properties to commercial paper used in packaging. Three CNFs were tested: mechanical (m-CNFs), by TEMPO mediated oxidation (T-CNFs) and carboxymethylated (c-CNFs). Two metering systems (wound rod and blade micrometer) were used to apply one, five and 10 layers of CNFs suspensions, and two drying methods (hot air jet and contact with a hot polished surface in a speed dryer) were evaluated. The quality of the CNFs coated papers was measured by structural (thickness, roughness and air permeance) and optical properties (gloss) and visual appearance. c-CNFs coatings obtained the lowest air permeance values, from 0.1 to 0.01 mu m/Pa.s depending on the number of coating layers, and were below those of commercial starch. T-CNFs also reduced air permeance at low weights, reaching 1.1 mu m/Pa.s with one layer and 0.1 when five layers were applied. Five layers of m-CNFs were needed for good results. SEM images showed good coverage at low coat weight in c-CNFs and T-CNFs, whereas m-CNFs was unable to cover the base paper. With increased layers of m-CNFs, an adequate film was formed. c-CNFs had the highest fibrillation degree and acid group content, and was the CNFs coating with most potential as a coating for paper.