Permanent hydrophobic coating of chitosan/cellulose nanocrystals composite film by cold plasma processing

A highly effective ultrafast chemical modification of chitosan/cellulose nanocrystals composite film surface is presented in the present research. Added value properties were achieved by the use of a few seconds' treatment with RF-generated low-temperature fluorocarbon plasma. Drastic increase of the water-repelling character of the completely natural-based biocomposite foil were observed, with contact angle reaching up to 121 degrees. Surface fluorination occurred through formation of irreversible fluorine-related bonds (CF-CF2, CF2-CF2 and C-CF, CF3 and O-CF2, O-CF3) detected by the means of X-ray photoelectron spectroscopy. Surface structural changes were further confirmed with ATR-FTIR. With packaging application in mind, the films were subjected to analysis of mechanical and water-related properties, showing an improvement upon fluorination. Further the stability of the modification was followed by measurements of water contact angle and atomic composition, as well as mechanical properties, water content and water vapor transmission after at least 31 days of storage in controlled environment. Lastly, no leaching of fluorinated components into liquid environments was detected by the means of HILIC LC-MS analyses in ESI(+) and ESI(-) modes. The presented method rapidly enhances the hydrophobic character of chitosan/nanocellulose biocomposite films without receding mechanical strength and provides a long-lasting surface coating.