Tailoring Structure and Barrier Properties of Cellulose Nanofibril Films via Low-Fraction Chitin Nanofiber Addition and Thermal-Mechanical Compaction

Abstract We investigated the effects of chitin nanofiber (ChNF) incorporation and a subsequent hot-press compaction step on the mechanical and barrier properties of cellulose nanofibril (CNF)-based films for food-packaging applications. CNF/ChNF films containing 5−20 wt % ChNF were prepared to examine how ChNF incorporation modifies the structure and performance of a CNF-rich nanofibrillar network. Fourier-transform infrared spectroscopy confirmed strong interfacial hydrogen bonding and ionic electrostatic interactions between the carboxyl/hydroxyl groups of CNFs and the protonated amino/hydroxyl groups of ChNFs. Water contact angle measurements revealed that all films remained hydrophilic, displaying low contact angles due to the abundance of accessible surface hydroxyl and protonated amine groups. The incorporation of minor ChNF fractions into the CNF matrix yielded non-additive synergistic improvements in mechanical strength and barrier performance. Incorporating only 10 wt % ChNF into CNF (without compaction) increased tensile strength to a peak of 128 MPa. Concurrently, adding 5 wt % ChNF significantly reduced OP from 60,000 cm3·μm·m−2·day−1·atm−1 for neat ChNF to about 600 cm3·μm·m−2·day−1·atm−1. Subsequent hot-press compaction further densified the composite network, achieving optimal properties at 5 wt % ChNF loading, including the lowest water vapor permeability (5.79 g·mm·m−2·day−1·kPa−1), the lowest OP 480.2 cm3·μm·m−2·day−1·atm−1, and the highest Young’s modulus of 4868 MPa. The films indicated no significant antibacterial activity. The results demonstrate that a small ChNF fraction can modify the performance of a CNF-rich film network, while hot-press compaction further improves barrier performance and stiffness through structural densification. The combined effects of CNF/ChNF composition and thermal-mechanical compaction provide a practical approach for developing renewable, high-barrier films for food-packaging applications.