Cellulose nanocrystals (CNCs) and chitin nanowhiskers (ChNWs) have high strengths and low oxygen permeabilities (OP), providing a sustainable substitute for petroleum-based plastics in food packaging applications. Their aqueous suspensions can be applied as coatings on a substrate film and function as an oxygen barrier. Because partially deacetylated chitin is cationic in acidic solution while sulfate-modified cellulose is anionic, the electrostatic attraction between the opposite charges enables their fabrication into multilayered coatings.

In this work, ChNWs and CNCs were spray-coated on cellulose acetate (CA) film as a bilayer oxygen barrier to obtain a transparent film. The properties of coated films were tuned by adjusting the spray coating temperature (T_spray) and the post thermal treatment temperature (T_thermal). By increasing T_spray from 40 to 100 °C and increasing T_thermal from 40 to 140 °C, the OP decreased 48% (from 44.3 ± 1.3 to 23.3 ± 3.9 cm³-μm/m²/day/kPa) and 62% (from 27.3 ± 1.2 to 11.5 ± 0.9 cm³-μm/m²/day/kPa), respectively. The optimal result was 98% lower than that of neat CA and is comparable to the OP of commercial oriented poly(ethylene terephthalate). The water vapor barrier and mechanical properties were not significantly influenced by adjusting the temperatures. The water vapor transmission rate for a coated film was on average 11% lower than neat CA film, and the coating of ChNW and CNC improved the ductility of the film in comparison to neat CA. Aerobic soil biodegradation studies indicate that the bilayer coatings can convert to CO₂ with a yield of 95% in 70 days. These properties support the utilization of CA film coated with a bilayer of ChNW and CNC as a sustainable substitute in packaging applications.

Callie Goins

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