Grafting nature-inspired and bio-based phenolic esters onto cellulose nanocrystals gives biomaterials with photostable anti-UV properties

New nature-inspired and plant-derived p-hydroxycinnamate esters and p-hydroxycinnamate diesters provide excellent protection against UV radiation when incorporated into a matrix. Herein, an efficient and sustainable pathway is reported to graft these phenolic compounds onto cellulose nanocrystals (CNCs) via click-type copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The successful grafting of the phenolic esters on CNC surface was evidenced by a range of chemical analyses, and the degrees of substitution (DS) of the CNC were found to depend on the structure of the phenolic ester grafted. Moreover, aqueous suspensions of the phenolic ester-grafted CNCs not only strongly absorb in both the UVA and UVB regions, but they also exhibit average to very high photostability. Their wide spectrum UV-absorbing properties and their stability upon exposure to UV are highly influenced by the structure of the phenolic ester, particularly by the extra ester group in p-hydroxycinnamate diesters. These findings demonstrate that cellulose nanocrystals decorated with such plant-derived and nature-inspired phenolic esters are promising sustainable nanomaterials for anti-UV applications.