High barrier bio-nanocomposite films of ethyl cellulose integrated with modified nanocellulose: effect of nanocellulose's substituted side chains on film performance†

Bio-based packaging films with good barrier properties to preserve quality, ensure safety, and extend the shelf-life of food products are in great demand as our society becomes more environmentally conscious. Herein, entirely bio-based nanocomposite films of the ethylcellulose (EC) matrix, reinforced with modified nanofibrillated cellulose (mNFC), have been studied. The NFC modification consisted in a microwave-assisted esterification reaction with three different acids – lactic acid (LA), lauric acid (LU), and stearic acid (SA) – of varying carbon chain lengths, in three solvents (water, ethanol, and ethyl acetate). The highest degree of substitution (DS) for mNFC-LA was achieved in ethanol, while mNFC-LU and mNFC-SA showed the maximum DS (up to 1.22) in ethyl acetate. The success of NFC surface modification was confirmed by titration, FTIR, XRD, SEM, and nanocellulose dispersion behavior. The films of EC-based nanocomposites were prepared by solvent casting and then examined for surface morphology, microstructures, mechanical properties, surface properties and barrier properties against water vapor and oxygen transmission. The findings revealed that integrating mNFC into EC can greatly improve the properties of the films due to their good compatibility, good dispersion ability, and strong interface, which is influenced by the substituted side chain on the mNFC surface. For the best side chain length (3 carbon atoms), mNFC-LA increased the tensile strength of the EC film by up to 130% while reducing the oxygen transmission rate (OTR) by 98%, making it a viable and environmentally benign alternative to PET films. This research offers insights into employing various modified nanocellulose to improve biopolymer-based films for high-barrier packaging and coating applications.