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Grafting novel and nature-inspired phenolic esters onto cellulose nanocrystals (CNCs) provides nanofibers with excellent protection against UV radiation when incorporated into a polymer matrix. In this work, CNCs decorated with a novel UVabsorbing phenolic diester (CNC-diethyl ferulate or CNC-DEF) obtained via a click-type copper-catalyzed azide/alkyne cycloaddition reaction were incorporated into a polyvinyl alcohol (PVA) matrix to produce transparent films with excellent photostability and UV-absorbing properties. PVA films filled with 20 wt % CNC-DEF exhibited complete UV protection (0% transmittance) and high transparency in the visible region (70− 90% transmittance). In contrast, PVA films loaded with the pristine CNCs do not show any UV-shielding properties. Importantly, the grafting of DEF moieties on CNCs significantly aids the dispersion of the phenolic diester in the aqueous PVA matrix, which was not achieved with DEF blended with PVA. Mechanical tests also show that the addition of 20 wt % CNC-DEF in PVA increases the tensile strength and modulus by 91 and 150%, respectively, relative to neat PVA. The oxygen barrier properties of the composite film also improve with CNC-DEF addition. This study shows the great potential of the phenolic-ester-decorated CNCs as dispersible, multifunctional UV-absorbing nanoreinforcements in PVA films for industrial and packaging applications.

The study showed that the antioxidant, anti-inflammatory, antiangiogenic and GST-inducing activities of betalains from red dragon fruit peels were enhanced through carbohydrate encapsulation. © 2016 Society of Chemical Industry.

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.

A family of thermoresponsive poly­(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) was synthesized via a novel silver-promoted decarboxylative polymerization approach. This method relies on the oxidative decarboxylation of carboxylic acid groups to initiate free radicals on the surface of CNFs. The polymerization reaction employs relatively mild reaction conditions and can be performed in a one-step, one-pot fashion. This rapid reaction forms a CC bond between CNF and PNIPAM, along with the formation of free polymer in solution. The degree of functionalization (DF) and the amount of PNIPAM grafted can be controlled by the Ag concentration in the reaction. Similar to native bulk PNIPAM, PNIPAM-grafted CNFs (PNIPAM-g-CNFs) show remarkable thermoresponsive properties, albeit exhibiting a slight hysteresis between the heating and cooling stages. Grafting PNIPAM from CNFs changes its cloud point from about 32 to 36 °C, influenced by the hydrophilic nature of CNFs. Unlike physical blending, covalently tethering PNIPAM transforms the originally inert CNFs into thermosensitive biomaterials. The Ag concentration used does not significantly change the cloud point of PNIPAM-g-CNFs, while the cloud point slightly decreases with fiber concentration. Rheological studies demonstrated the sol–gel transition of PNIPAM-g-CNFs and revealed that the storage modulus (G′) above cloud point increases with the amount of PNIPAM grafted. The novel chemistry developed paves the way for the polymerization of any vinyl monomer from the surface of CNFs and carbohydrates. This study validates a novel approach to graft PNIPAM from CNFs for the synthesis of new thermoresponsive and transparent hydrogels for a wide range of applications.

Inspired by nature’s photoprotection mechanisms, we report an effective UV-blocking nanomaterial based on diethyl sinapate-grafted cellulose nanocrystals (CNC-DES). The colloidal stability and UV-blocking performance of CNC-DES in aqueous glycerol (a common humectant in petroleum-free cosmetic formulations) and in a commercially available moisturizing cream were studied. Grafting the water-insoluble DES onto CNCs renders it dispersible in these water-based formulations, thanks to the excellent water-dispersibility of CNC nanoparticles. Glycerol dispersions containing 0.1 to 1.5 wt% CNC-DES display very high UV-blocking activity owing to the anti-UV DES moieties anchored onto CNCs. A facial cream blended with 1.5 wt% CNC-DES exhibits an SPF of 5.03, which is higher than a commercially available sunscreen with the same active ingredient concentration (SPF = 3.84). DPPH radical scavenging assay also showed the antioxidant potential of CNC-DES, albeit coinciding with a significant reduction in antioxidant activity after grafting DES onto CNCs. Cytotoxicity measurements revealed the CNC-DES not to cause significant cytotoxicity to murine fibroblast cells after 24 h of exposure. Overall, CNC-DES exhibits strong anti-UV and antioxidant properties and is water-dispersible, biocompatible, non-greasy, and lightweight. This study demonstrates the exceptional potential of DES-grafted CNCs as nature-inspired UV filters in the next generation of cosmetic formulations, including those for sensitive skins.

Invited for this month's cover is the international collaborative work from the Bioresource Processing Research Institute of Australia (BioPRIA)‐Monash University and URD Agro‐Biotechnologies Industrielles (ABI)‐AgroParisTech. The cover image shows how the grafting of Nature‐inspired and bio‐based phenolic esters on cellulose nanocrystals through click‐chemistry provides materials with highly photostable UV‐blocking properties. Cover art by David Mendoza. The Full Paper itself is available at 10.1002/cssc.202002017.