Synergistic role of lignin nanoparticles and microfibrillated cellulose in high-barrier coatings for recyclable 3D-formed fiber packaging

The growing demand for sustainable and recyclable alternatives to plastic packaging has driven the development of 3D-formed fiber-based materials. While fiber-based packages are biodegradable and compatible with paper recycling streams, their high porosity and poor resistance to moisture and grease limits their use in food packaging applications. Herein we demonstrate a scalable, biobased dispersion coating strategy based on tall oil fatty acid–esterified lignin nanoparticles (TOFA-LNPs) within microfibrillated cellulose (MFC) enhancing the barrier performance of 3D-formed fiber trays. A solvent shifting approach was employed to produce stable TOFA-LNPs, enabling their use in aqueous dispersions. The combination of MFC and TOFA-LNPs provides a synergistic effect: MFC provides excellent film formation, while TOFA-LNPs impart hydrophobicity and a plasticizing effect, mitigating the hygroscopicity of MFC and the poor film-forming ability of lignin. The coatings were applied using air-spray coating, and their effectiveness was evaluated in terms of water, oil, and water vapor resistance, as well as recyclability, and compared to that of coatings prepared with unmodified LNPs. Trays coated with TOFA-LNP/MFC at 1:2 nanoparticle-to-MFC ratio exhibited the best overall performance, showing reduced water absorption of 126 g/m 2 and water vapor transmission rate of 158 ± 11 g/m 2 ·day, improved hydrophobicity, and enhanced grease resistance. The barrier performance correlated with coating morphology and surface free energy. All coated trays retained full recyclability in paper stream. The use of aqueous dispersions and spray coating highlights the industrial relevance and scalability of this approach, offering a promising pathway toward recyclable fiber-based food packaging aligned with circular economy principles and emerging regulatory requirements. • Synergistic TOFA-LNP/MFC structures improved film formation and lowered coating wettability. • Spray-coated TOFA-LNP/MFC formulations enhanced water, oil, and vapor barrier properties. • Coated 3D-formed fiber trays remained fully recyclable in conventional paper recycling streams.