Resilient high oxygen barrier multilayer films of nanocellulose and polylactide

Nanocelluloses are promising high gas barrier materials for biobased food packaging, but they must be protected from water to preserve high performance. The respective O₂ barrier properties of different types of nanocelluloses were compared (nanofibers (CNF), oxidized nanofibers (CNF TEMPO) and nanocrystals (CNC)). The oxygen barrier performance for all types of nanocelluloses was similarly high. To protect the nanocellulose films from water, a multilayer material architecture was used with poly(lactide) (PLA) on the outside. To achieve this, a biobased tie layer was developed, using Corona treatment and chitosan. This allowed thin film coating with nanocellulose layers between 60 and 440 nm thickness. AFM images treated with Fast Fourier Transform showed the formation of locally-oriented CNC layers on the film. Coated PLA(CNC) films performed better (3.2 × 10^-20 m³.m/m².s.Pa) than PLA(CNF) and PLA(CNF TEMPO) (1.1 × 10^-19 at best), because thicker layers could be obtained. The oxygen barrier properties were constant during successive measurements at 0 % RH, 80 % RH and again at 0 % RH. This shows that PLA is sufficiently shielding nanocelluloses from water uptake to keep high performance in an extended range of RH and opens the way to high oxygen barrier films which are biobased and biodegradable.