Biobased barrier dispersion coating from solvent shifting of functionalized lignin inside cellulose nanofibers aqueous suspensions

In this study, we present a simple one-pot approach to formulate barrier dispersions by combining nanoscaled cellulose and lignin, while harnessing the hydrophobizing effect of tall oil fatty acid (TOFA) modification. Using an in situ solvent-shifting method, unmodified lignin and TOFA-esterified lignin solutions were directly incorporated into aqueous microfibrillated cellulose (MFC) suspensions, enabling the in situ formation of stable lignin nanoparticles (LNPs and TOFA-LNPs) within the MFC matrix. Nanopapers prepared from TOFA-LNP:MFC dispersion with a ratio of 1:2 exhibited excellent barrier properties, with a water vapor transmission rate of 6 g/m²·day (50 % RH, 23 °C), an oil Cobb1800 value of 0.3 g/m², and a water Cobb1800 value of 12 g/m². The results demonstrate that TOFA modification of lignin and its incorporation within the MFC matrix as nanoparticles, facilitates the formation of dense, uniform films with strong resistance to moisture and oil. To gain a deeper understanding of the system, surface-sensitive quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM) were used to analyze how the TOFA modification of lignin affected its physicochemical interactions within cellulose fibrils. Furthermore, humidity-controlled QCM-D measurements were used to analyze the effect of lignin-based nanoparticles on the water vapor adsorption behavior of MFC at different relative humidities providing new insights into their barrier performance, explored here for the first time. Finally, the successful application of dispersion coatings onto commercial fiber-based substrates demonstrates their industrial potential. This work introduces a versatile and scalable route to fully biobased coatings, advancing the transition toward circular and sustainable packaging solutions.