Transparent Composite Films of Cellulose Nanofibrils and Nanocrystals for Modified Atmosphere Packaging

Modified atmosphere packaging (MAP) is critical for preserving the quality of fresh foods, but most existing packaging materials lack sustainability and environmental compatibility. Herein, sustainable and transparent composite nanocellulose films with tunable barrier properties were developed via solution casting using varying ratios of TEMPO-oxidized cellulose nanofibrils (TOCNF) and cellulose nanocrystals (CNC). All films maintained high transparency (88.76–89.87% at 550 nm), while haze decreased from 21.77% to 11.34% with increasing CNC content from 20 to 80%. The composite film containing 50% TOCNF (FC-50) exhibited the most balanced barrier performance, with the lowest oxygen transmission rate (23.52 cm3/m2·24 h·0.1 MPa) and a moderate water vapor permeability (4.47 × 10–10 g/(m·s·Pa)), making it suitable for MAP applications. FC-50 also demonstrated excellent mechanical properties, with a tensile strength of 60.58 MPa and a fracture toughness of 3.393 MJ/m3. In strawberry preservation and biodegradation tests, FC-50 effectively reduced weight loss, degraded after 60 days, and maintained fruit brightness, outperforming both air-exposed and PVDC-wrapped controls. Unlike PVDC films with extremely low vapor permeability, FC-50 minimized moisture condensation while allowing appropriate gas exchange, thereby extending shelf life. These results underscore the potential of composite nanocellulose films as sustainable, biodegradable MAP materials for fresh produce packaging.