Facile fabrication of transparent cellulose films with high water repellency and gas barrier properties

Transparent and water repellent gas barrier cellulose films were fabricated by surface modification of alkali/urea regenerated cellulose (AUC) films by soaking in cationic alkylketene dimer (AKD) dispersion, drying, and heating. Highly water repellent and excellent gas barrier properties were obtained for AKD-treated and heated AUC films due to covering of the film surfaces by hydrophobic AKD components. The maximum AKD content of the films was 0.2 %. Oxygen transmission rates for AKD-treated AUC films at 0 % relative humidity (RH) were less than 0.0005 mL m⁻² day⁻¹ kPa⁻¹, the lowest detection limit of the instrument. Water contact angles on the AUC film increased from 50 to 110° after AKD treatment, and water uptake (immersion in water for 6 days) decreased from 92 to 20 %. Moreover, oxygen permeability decreased from 0.56 and 5.8 to 0.13 and 2.1 mL μm m⁻² day⁻¹ kPa⁻¹ at 50 and 75 % RH, respectively, when the AKD content of the film was increased from 0 to 0.2 %. The present AKD-treated AUC film also had high light transparency (88 % at 600 nm), tensile strength (168 MPa), elongation at break (29 %), and work of fracture (37 MJ m⁻³). FT–IR analysis showed that AKD components were still present as major species on the AKD-treated film surfaces without hydrolysis at 2 months after conditioning the films at 23 °C and 50 % RH, indicating that such AKD molecules contributed to the hydrophobic nature of the AKD-treated AUC films.