Barrier Properties of Lab and Semi-pilot Coatings with Different CNF Formulations, TAPPICon25

Two types of cellulose nanofibrils (CNF) were produced to prepare coating formulations: enzymatically pre-treated CNF (CNF-Gen1) and carboxymethylated CNF (CNF-Gen2). Different formulations were prepared varying the solid content percentages and the amounts of carboxymethylated cellulose - CMC. Specifically, CNF-Gen2 at 1.2 wt% and 2 wt%, and CNF-Gen1 at 2 wt% combined with different amounts of CMC (2.5, 5, 10 and 20 wt%) were selected based on their water retention and rheological properties. A coat weight of 5 g/m2 was chosen as optimum to be the minimum coating required to reduce the air permeability to 0.003 μm/Pa.s. Among the formulations, CNF-Gen1+10wt%CMC and CNF-Gen2 at 1.2 wt% showed the best performance in terms of applicability, rheology, air permeability and oil barrier properties. Both of these formulations were successfully applied on two substrates (paper and board) using a semi-pilot Comma coating unit, enabling multilayer coatings without any web breakage or any expected problems related to high water content in the coatings. However, the paper substrate showed some wrinkles that were partially solved by adding PVA as a pre-coating layer and the board substrate presented a non-homogenous coating with the CNF-Gen1+10%CMC. New coating formulations were prepared by combining both types of nanocelluloses coatings (90%CNF-Gen1+10%CMC and 10% CNF-Gen2) showing an improvement in the processability and coating quality. Air permeability was drastically reduced with the application of all the coatings. Water resistance was kept in the case of the paper substrate and even reduced by 50% in the case of some coatings on the board. Almost all the coating systems passed the oil test. The influence of the pre-coating layer and the number of layers in the coating was also evaluated. Coatings without PVA show comparable results to the ones pre-coated.

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