Fabrication of Water-Resistant and Structure-Reinforced Chitin Nanofibril Films with Fruit-Preservation Functionality via a Green, Facile, and Scalable Strategy

Chitin nanofibril (ChNF)-based films, known for their renewability and biodegradability, are limited by their poor water resistance. Herein, a green, facile, and scalable strategy was proposed to enhance their water resistance as well as mechanical properties. The succinic acid (SA) in place of commonly used monocarboxylic acid was used first as a proton donor to facilitate disintegration of chitin into ChNFs or chitin microfibrils (ChMFs), and subsequently as a latent thermo-cross-linking agent to covalently cross-link the ChNF/SA cast films by a simple heat treatment, achieving the swelling degree (SD) as low as 96.5 ± 8.3% and tensile strength (TS) up to 104.06 ± 6.75 MPa. Based on that, ChMF as a long-range entanglement contributor was incorporated to yield the ChNMF/SA cast films, further reducing SD to 71.3 ± 4.2% and improving wet-state TS from 7.6 ± 1.1 to 10.6 ± 0.4 MPa. To expand application scenarios, tannic acid (TA) as a functional additive was introduced and endowed the resultant films (ChNMF/SA/TA) with excellent antioxidant, antibacterial, UV-shielding, and strawberry-preservation performances. In brief, this study demonstrated a simple method to create water-resistant, mechanically robust ChNF-based films with great potential for sustainable fruit packaging application.