Oxidative crosslinking for the development of barrier coatings utilizing lignin-containing cellulose nanofibrils and lignin nanoparticles

We developed a bio-based barrier coating utilizing lignin as the primary coating material on lignin-containing cellulose nanofibrils (LCNFs). To enhance the hygroscopic properties of LCNF, we employed enzymatic crosslinking as a green modification strategy, combined with the deposition of lignin nanoparticles (LNPs) and tall oil fatty acid (TOFA)-esterified LNPs as a functional coating layer. A laccase-catalyzed oxidative system was introduced to establish a three-dimensional crosslinked network within LCNF, facilitating the covalent bonding of LNPs to the film surface while reinforcing interparticle crosslinking. The successful attachment of LNPs was confirmed via surface plasmon resonance (SPR) measurements and atomic force microscopy (AFM). Nanoindentation tests further demonstrated increased film rigidity following enzymatic crosslinking. To ensure good barrier performance, uniform surface coverage was achieved using layer-by-layer (LbL) deposition of LNPs and cationic starch, followed by enzymatic grafting and heat treatment. Notably, the laccase-catalyzed modification significantly improved the oxygen barrier performance, reducing oxygen permeability (OP) by 50 % under 80 % relative humidity compared to uncrosslinked films. The TOFA-LNP coating further enhanced barrier properties, achieving 2–3 times lower OP depending on coating thickness. Additionally, the coated films exhibited superior UV-shielding and antioxidant properties, while overall migration values remained below 10 mg/dm², underscoring their potential as environmentally friendly, high-performance barriers for food packaging in high-humidity conditions.