Cellulose Nanofiber Films With Enhanced Wet Strength, UV‐Blocking, Antibacterial, and Antioxidant Properties Through Surface‐Modified Cellulose Nanocrystal and Tannic Acid

ABSTRACT Cellulose nanofiber (CNF) based films usually suffer from poor water resistance and low wet strength, so it is highly desired to fabricate CNF‐based films with high wet strength and additional functions to promote their applications. Herein, UV‐blocking, antibacterial and antioxidant CNF‐based films with high wet strength were prepared by using surface‐modified cellulose nanocrystal (mCNC) as novel nanocrosslinker and naturally occurring tannic acid (TA) as multifunctional additive. Relying on its grafted polyacrylamide chains, mCNC served as an effective nanocrosslinker for both dry and wet CNF films, thereby enhancing both dry and wet strength of the film. The optimum CNF/mCNC composite film showed a dry tensile strength of 95 MPa and wet tensile strength of 17 MPa, which are 2.16‐ and 5.67‐fold higher than pure CNF film, respectively. Further introduction of TA endowed CNF/mCNC/TA composite films with outstanding UV‐blocking (near zero transmittance at 200–365 nm), antibacterial and antioxidant capacity, but at the cost of reduced mechanical performance due to its plasticizing effect. However, wet CNF/mCNC/TA composite films with moisture contents of 62%–64% still showed an utmost tensile strength of 9.5 MPa. Hence, a combination of high wet strength and multifunction makes the developed CNF/mCNC/TA composite films promising candidates for bio‐based active food packaging.