Effect of Silybum marianum-derived nanocellulose as a sustainable functional filler on supramolecular structure of thermoplastic zein

Thermoplastic zein (TPZ)-based bioplastics offer a promising alternative to conventional ones. However, they exhibit certain limitations, notably in terms of mechanical strength and barrier properties. These properties can potentially be enhanced by using fillers, such as nanocellulose, to produce nanocomposites. In this study, bio-based nanocomposite films were produced using a compression molding and melt mixing approach, employing TPZ in combination with two different types of Silybum marianum (SM)-derived nanocellulose, cellulose nanocrystals (SM_CNC) or cellulose nanofibers (SM_CNF), at different concentrations (3 wt%-10 wt%). The effect of different nanocelluloses on the structure of TPZ was studied by means of X-ray diffraction and correlated with mechanical, thermal and physical properties (water permeability and UV resistance) obtained by TGA, DMA, and mechanical, permeability and spectrophotometric tests. Incorporation of both types of nanocellulose yielded changes in film properties, according to filler concentration. The results demonstrated that SM_CNC and SM_CNF increased the mechanical properties only at 5 wt%, raising the modulus by 25 % and 27 %, respectively. Barrier property studies revealed that both nanocelluloses also improved the water resistance of TPZ bio-nanocomposites but at a lower concentration (3 wt%) at which relevant protein structural changes occurred. Therefore, the developed bio-nanocomposites possess versatile properties that make them promising candidate for packaging materials for different foods.