Highly transparent, strong and flexible films with modified cellulose nanofiber bearing UV shielding property.

This work investigates multifunctional composite films synthesized with cellulose nanofibers (CNFs) and poly (vinyl alcohol) (PVA). First, TEMPO-oxidized CNFs were modified in heterogeneous phase with benzophenone, diisocyanate and epoxidized soybean oil via esterification reactions. A thorough characterization was carried out via elemental analysis as well as FT-IR, X-ray photoelectron spectroscopies, and solid-state NMR. Following, the surface-modified CNFs where combined with PVA to endow composite films with UV-absorbing capabilities while increasing their thermo-mechanical strength and maintaining a high light transmittance. Compared to neat PVF films, the strength at break, Young modulus and elongation of the films underwent dramatic increases upon addition of the reinforcing phase (maximum values of ~96 MPa, ~714 MPa and ~350%, respectively). A high UV blocking performance, especially in the UVB region, was observed for the introduced multifunctional PVA films at CNF loadings below 5 wt%. The tradeoff between modified nanofibril function as interfacial reinforcement and aggregation leads to an optimum loading. The results indicate promising applications, for example, in active packaging.