Double-Layer Barrier Coating of Paperboard Using Cationic Cellulose Micro/Nanofibers and Waterborne Acrylic Water-Repellent Agent

In this study, a double-layer coating system to improve the barrier properties of linerboard was developed using either a quaternized cellulose microfiber (Q-CMF) or a quaternized cellulose nanofiber (Q-CNF) layer and a waterborne acrylic water-repellent agent (WAWR) layer.Q-CMFs and Q-CNFs were prepared from bleached hardwood kraft pulp and modified via a quaternization reaction using glycidyltrimethylammonium chloride.The cationic cellulose fibers were applied as a pre-coating layer, followed by top coating with an anionic WAWR.The effects of the degree of fibrillation on coating performance and barrier properties were systematically evaluated.The results showed that Q-CNF exhibited higher viscosity and zeta potential than Q-CMF due to its greater degree of fibrillation and larger specific surface area.In the single-layer coating system, Q-CNF formed a denser coating structure by effectively filling inter-fiber pores, resulting in superior air barrier performance.However, cellulose-only coatings exhibited limited water repellency due to the hydrophilic properties of the cellulose.In the double-layer coating system, the Q-CNF/WAWR-coated paper exhibited the best overall performance.Despite having approximately 20% lower coat weight (6.3 g/m 2 ) than the Q-CMF/WAWR coating, the Q-CNF/WAWR exhibited an enhanced burst strength of 11.9 kg f /cm 2 and excellent barrier properties.The air resistance increased to 545 s, approximately 12 times that of the uncoated linerboard, while the water repellency achieved the highest grade, R10.FE-SEM analysis confirmed that the Q-CNF effectively sealed the porous paper by forming a dense coating layer.