Energy-Efficient Pilot-Scale Coating of Cellulose Nanofibrils Using Controlled Vacuum Deposition, TAPPICon26

The transition of cellulose nanofibril (CNF) coatings from laboratory studies to industrial roll-to-roll production requires a process capable of achieving high coat weights and solids contents in a single step. Conventional rod and blade systems often produce low coat weights (< 3 g m⁻²) as shear flow generates a thin water layer that inhibits fibril deposition, resulting in low solids deposition and an increased drying demand. To overcome these limitations, a pilot-scale vacuum-assisted coating unit was developed to replicate industrial geometries while allowing precise control of web speed, vacuum length, and applicator gap. The system employs a stationary metering rod above a moving web with adjustable vacuum zones, enabling controlled dewatering and consolidation of CNFs during coating. Using suspensions of 0.4–0.6 wt % solids and vacuum lengths of 20–170 mm, coat weights between 6 and 12 g m⁻² were achieved at line speeds up to 20 m min⁻¹. Barrier performance scaled directly with coat weight, yielding Cobb Oil reduction by more then 80% and Gurley air resistances above 3 × 10⁴ s. A predictive model combining Darcy-type filtration with geometric gap entrainment accurately replicated these experimental trends, allowing process-level control of coat-weight outcomes. The mass balance shows a potential cost decrease for the water removal of more than 80%. Overall, vacuum-assisted coating of CNFs provided an energyefficient, scalable framework for the continuous production of PFAS-free, paper-based barrier coatings suitable for sustainable food-packaging applications.

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