Anisotropy control of GO-CNC nanofillers in chitosan-based ultrasonic-sprayed nanocomposite coatings to improve oxygen and water vapor barrier properties of PBS films

This study compares two sustainable polymer-based nanocomposite coating architectures: a single-layer coating composed of chitosan (CH), graphene oxide (GO), and cellulose nanocrystals (CNC), cross-linked with borax (B), and a bilayer system in which an outer layer containing GO and borax-crosslinked CNC is applied onto a borate-crosslinked CH matrix incorporating GO. The two systems were designed to highlight the effect of the spatial segregation of the fillers in improving the oxygen and water vapor barrier performance of polybutylene succinate (PBS) films, evaluating an isotropic or anisotropic distribution of fillers across the coating thickness, while maintaining a bio-based and environmentally friendly material platform. Swelling tests confirmed that borax effectively crosslinks the nanocomposite material comprised of both GO and CNC, significantly enhancing the water swelling resistance of the coating formulations. Morphological analysis revealed compact, defect-free structures with uniform nanofiller dispersion and orientation in the nanocomposite single-layer, while the biayer system exhibited a highly aligned GO in the bottom layer and a compacted filler network in the upper layer. Gas barrier test showed that oxygen permeability was reduced by up to three orders of magnitude at 5% RH and by one order at 50% RH, compared to uncoated PBS. Water vapor permeability (WVP) was also improved, particularly in the bilayer coating, where WVP decreased by 25%. These findings highlight the effectiveness of tailored nanofiller distribution and hybrid filler generation in developing high oxygen and water barrier sustainable coatings, suitable for oxygen-sensitive packaging in humid environments.