In situ polymerization of lignin in cellulose nanofibrils aqueous dispersion for fully bio-based barrier coating in packaging

Using cellulose nanofibrils (CNF) in packaging under humid conditions is challenging due to their hygroscopicity, which causes an efficacy-failure of coating materials. Here, inspired by nature and plant cell walls, we developed a fully bio-based aqueous dispersion coating made of CNF/ polymerized lignin, where lignin was polymerized in situ in proximity to a CNF surface in dispersion via laccase-catalyzed oxidation. The polymerized lignin nanoparticles were evenly distributed on the fiber surface in CNF/ polymerized lignin dispersions, particularly in isopropyl alcohol (iPrOH) lignin fractions at a loading amount of 15 wt% and for an enzymatic polymerization of 6 h. This dispersion also demonstrated the formation of homogenous films with the highest hydrophobicity (a water contact angle of approx. 120°) among all tested formulations. The iPrOH-lignin fractions outperformed other fractions in enhancing the barrier properties of the coated paperboard, i.e., a twofold reduction in the water vapor transmission rate, a 52-fold reduction in the oxygen transmission rate, and excellent grease barrier properties (KIT rating of 12). These results indicate that aqueous dispersion coatings of CNF/ polymerized lignin reveal the structure–property relationship between the decoration of the CNF surface and the performance of the coating, which are a promising sustainable approach for providing barrier properties in packaging applications.