Transparent TEMPO-oxidized cellulose nanofiber film with enhanced ultraviolet-shielding and surface wettability by lignin nanoparticle

Nanocomposite films based on TEMPO-mediated oxidized cellulose nanofiber (TOCNF), glycerol as a plasticizer, and lignin nanoparticle (LNP) were fabricated via a simple spray deposition technique to investigate the effect of LNP on the film properties. All films were transparent and flexible, and scanning electron microscopy observation confirmed that the LNPs were integrated into the TOCNF matrix structure. The presence of LNPs endowed the films with UV-shielding capability due to aromatic rings in the structure: Films containing LNPs at 10 wt% achieved 100 % UV-shielding at 378 nm, whereas films without LNPs showed only about 20 % shielding at the same wavelength. LNPs also enhanced surface hydrophobicity, as indicated by an increase in the static water contact angle from 58° to 99°. While LNPs maintained the Young's modulus and tensile strength of the plasticized TOCNF films, they slightly reduced the elongation at break. Water vapor and oxygen barrier performances were decreased by LNP addition, although the amount of LNPs in the film did not clearly affect the properties. Overall, this study demonstrates that bio-based nanocomposite films with excellent UV-shielding properties and improved surface hydrophobicity have the potential to replace conventional petroleum-based packaging materials.