High water-vapor-barrier cellulose films via ice-induced crystallization and hydroxyl/carboxyl synergistic enhancement effect.

The potential environmental and health hazards of packaging materials based on petrochemical polymers have prompted a shift in research toward biodegradable polymers. However, most biodegradable films have poor water vapor barrier properties. We proposed an environmentally friendly method based on salting-out and cyclic freezing-thawing effects to improve the water-resistance and water vapor barrier properties of carboxymethyl cellulose (CMC)-based films. The coexistence of hydroxyl (OH) and carboxyl (COOH) was found to be crucial in promoting the ice-induced crystallization of cellulose molecules. The calculations of ice crystal size and freezable water weight content as well as hydrogen bonding theory analysis proved that the COOH can enhance the polymer interactions and crystallization to resist water molecules. The water vapor permeability (WVP) is as low as 3.89 × 10-11 g·m/m2·Pa·s at 37 °C and 65 % RH, a 6-fold reduction compared to the untreated CMC film. Meanwhile, the CMC-based films have high water resistance and mechanical strength, with a maximum wet tensile strength of 14.96 MPa, and remain intact after two months of immersion in water. This strategy is of great significance for the development of sustainable packaging materials with high barrier properties.